WO2004096422A1 - Particulate emulsifiers, emulsions and uses thereof - Google Patents

Particulate emulsifiers, emulsions and uses thereof Download PDF

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Publication number
WO2004096422A1
WO2004096422A1 PCT/GB2004/001913 GB2004001913W WO2004096422A1 WO 2004096422 A1 WO2004096422 A1 WO 2004096422A1 GB 2004001913 W GB2004001913 W GB 2004001913W WO 2004096422 A1 WO2004096422 A1 WO 2004096422A1
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Prior art keywords
emulsion
polymer
use according
water
latex
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PCT/GB2004/001913
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French (fr)
Inventor
Bernard P. Binks
Steven P. Armes
Catherine P. Whitby
Javier I. Amalvy
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The University Of Sheffield
The University Of Hull
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Publication of WO2004096422A1 publication Critical patent/WO2004096422A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D17/00—Separation of liquids, not provided for elsewhere, e.g. by thermal diffusion
    • B01D17/02—Separation of non-miscible liquids
    • B01D17/04—Breaking emulsions
    • B01D17/047—Breaking emulsions with separation aids
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
    • B01J13/0052—Preparation of gels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
    • B01J13/0052—Preparation of gels
    • B01J13/0056—Preparation of gels containing inorganic material and water
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K23/00—Use of substances as emulsifying, wetting, dispersing, or foam-producing agents
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K23/00—Use of substances as emulsifying, wetting, dispersing, or foam-producing agents
    • C09K23/017—Mixtures of compounds
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K23/00—Use of substances as emulsifying, wetting, dispersing, or foam-producing agents
    • C09K23/16—Amines or polyamines
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L33/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides or nitriles thereof; Compositions of derivatives of such polymers
    • C08L33/04—Homopolymers or copolymers of esters
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L39/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a single or double bond to nitrogen or by a heterocyclic ring containing nitrogen; Compositions of derivatives of such polymers
    • C08L39/04—Homopolymers or copolymers of monomers containing heterocyclic rings having nitrogen as ring member
    • C08L39/06—Homopolymers or copolymers of N-vinyl-pyrrolidones

Definitions

  • the present invention relates to the use of particles as emulsifiers in oil-in-water and water-in-oil emulsions.
  • Emulsions find application in a wide range of fields, for example food, agrochemicals, cosmetics, personal/home care product formulations, pharmaceuticals, tertiary- oil recovery, etc.
  • Low molar mass surfactants and surface- active polymers are well known as emulsifiers for use in the preparation of emulsions.
  • Fine particles are also known to act as emulsifiers. Emulsions stabilised by fine particles are often referred to in the art as “Pickering” or “Ramsden” emulsions.
  • Particulate emulsifiers known in the art include hydrophilic silica sols as emulsifiers for oil-in-water emulsions, and charge-stabilised latex particles as emulsifiers for water-in-oil emulsions.
  • hydrophilic silica sols as emulsifiers for oil-in-water emulsions
  • charge-stabilised latex particles as emulsifiers for water-in-oil emulsions.
  • particulate emulsifiers are colloidal rather than molecular in nature they may show lower toxicity and reduced irritancy to human skin compared to small molecule emulsifiers. Emulsions produced using particle- based emulsifiers also tend to be more stable to coalescence and the systems in general are more robust, and are therefore easier to make and reproduce.
  • Emulsions containing small molecule surfactants are prone to foaming as the emulsion' is being produced. This can cause significant problems when emulsions are produced on an industrial scale and addition of expensive silicon- based anti-foaming agents is often necessary. Particulate emulsifiers do not usually stabilise foams however and therefore very little foam or none at all is produced during formulation.
  • particle-stabilised emulsions are significantly more stable to breaking (e.g. demulsification) than small molecule-stabilised emulsions.
  • the particulate emulsifiers of the present invention may be recovered from the emulsions of the invention and reused.
  • the particles may be recovered by filtration, centrifugation etc.
  • the present invention provides the use of a particulate emulsifier comprising at least one polymer in an oil-in-water or water-in-oil emulsion, wherein the hydrophilic/hydrophobic balance of the polymer can be varied on application of a stimulus to break the emulsion, or to cause phase inversion.
  • the breaking, or phase inversion, of the emulsion is reversible.
  • the invention provides the use of a particulate emulsifier comprising at least one responsive polymer, wherein the stability of the emulsion is dependent on at least one environmental condition.
  • the invention is directed to oil- in-water and water-in-oil emulsions comprising at least one particulate emulsifier comprising a polymer wherein the hydrophilic/hydrophobic balance of the polymer can be varied on application of a stimulus to break the emulsion, or to cause phase inversion.
  • the invention is directed to oil- in-water and water-in-oil emulsions comprising at least one particulate emulsifier comprising a polymer wherein the stability of the emulsion is dependent on at least one environmental condition.
  • the invention further provides a method for stabilising an oil-in-water or water-in-oil emulsion comprising the use of a particulate emulsifier comprising a polymer wherein the hydrophilic/hydrophobic balance of the polymer can be varied by application of a stimulus.
  • the invention provides a method for the preparation of an oil-in-water or water-in-oil emulsion, comprising the use of a particulate emulsifier comprising a responsive polymer wherein the stability of the emulsion is dependent on at least one environmental condition.
  • the invention also provides a method of breaking an emulsion comprising a particulate emulsifier comprising at least one polymer, the method comprising applying a stimulus to vary the hydrophilic/hydrophobic balance of the polymer to an extent sufficient to break the emulsion, or to cause phase inversion.
  • the invention also provides a method of breaking an emulsion comprising a particulate emulsifier comprising at least one polymer, the method comprising varying at least one environmental condition to an extent sufficient to break the emulsion, or to cause phase inversion.
  • the particulate emulsifier is a polymeric microgel or has a core/shell latex structure.
  • the invention comprises each and every combination of preferred features disclosed herein.
  • Figure 1 Schematic representation of pH-responsive emulsification/demulsification using a sterically stabilised polymer latex.
  • FIG 2 Schematic representation of pH-responsive phase inversion using a sterically stabilised polymer latex
  • Figure 3 Air-water surface tension curve against pH for a number of dispersions of latex particles.
  • Figure 4 1 H NMR spectra of micelles and shell cross-linked (SCL) micelles as a function of pH.
  • PEO-DMA-DEA poly [ (ethylene oxide) -Jloc ⁇ -2- (dimethylamino) ethyl methacrylate- locJt-2- (diethylamino) methacrylate]
  • PEO-GMA-DEA poly [ (ethylene oxide) -jblocic-glycerol monomethacrylate-jblocj ! -2- (diethylamino) ethyl methacrylate]
  • DMA-MEMA poly [2- (dimethylamino) ethyl methacrylate-jlocJc-2- ( ⁇ V-morpholino) ethyl methacrylate]
  • PEO-DMA-MEMA poly [ (ethylene oxide) -block-2 - (dimethylamino) ethyl methacrylate-jlocc-2- (N- morpholino) ethyl methacrylate]
  • DMA-DEA poly [2- (dimethylamino) ethyl methacrylate-JIoc.fc-2- (diethylamino) methacrylate]
  • DMA DEA polyDMA-St n is approx 8 n is approx45
  • Emulsion is a mixture of immiscible liquids wherein one liquid is finely dispersed within the continuous phase of another.
  • Emulsions are generally characterised as oil-in-water emulsions, wherein oil droplets are dispersed in a continuous water phase, or water-in-oil emulsions, wherein water droplets are dispersed in a continuous oil phase.
  • the emulsifiers used according to the present invention are particles which have variable hydrophilicity or hydrophobicity.
  • the particles' affinity for water (or, conversely, oil) can be varied by varying at ' least one environmental condition.
  • the stability of emulsions comprising such particles is therefore dependent on the environmental conditions .
  • Particles are classed as hydrophilic if the contact angle they make with an oil-water interface (measured into the water phase) is less than 90 degrees. Particles are classed as hydrophobic if this contact angle is greater than 90 degrees.
  • Hydrophilic particles are more hydrophilic if the contact angle approaches zero. Hydrophobic particles are more hydrophobic if the contact angle approaches 180 degrees.
  • the particulate emulsifiers used according to the invention should have some affinity for both the oil and water phases of the emulsion.
  • the particles have affinity for both phases of the emulsion, the particles adsorb at the oil/water interface of the emulsion forming an adsorbed layer around the dispersed phase that prevents coalescence of the dispersed phase and therefore stabilises the emulsion.
  • the particles do not have affinity for both of the phases in the emulsion, or have significantly stronger affinity for one of the phases, the particles do not adsorb at the emulsion interface and so do not form a stabilising layer.
  • a stable emulsion in which the particles have affinity for both phases can therefore be broken by changing the hydrophilic/hydrophobic balance of the particle emulsifier such that the particle no longer has affinity for both phases of the emulsion, has a much stronger affinity for one phase of the emulsion relative to the other phase, or even has no affinity for either phase.
  • a stable emulsion is considered to be "broken" on the appearance of a macrophase caused by coalescence of the particles of the disperse phase.
  • Phase inversion occurs when an oil-in-water emulsion is converted into a water-in-oil emulsion, or vice versa. Phase inversion can occur directly, without the intermediate formation of a macrophase.
  • the particulate emulsifiers used according to the invention should remain essentially intact in either phase of the emulsion, that is, they should not completely disintegrate in either phase
  • the particle emulsifiers used in the present invention comprise at least one polymer which displays variable hydrophilicity/hydrophobicity depending on external conditions.
  • the term "responsive polymer” is used herein to describe any polymer whose hydrophilic/hydrophobic balance can be changed by varying one or more external condition (s) .
  • the polymer may respond to a variation of an external condition by, for example, a steric or conformational change, by a change in protonation or de-protonation, by a change in solvation, by a change in hydration, or by any other response leading to a change in the contact angle of the polymer particle surface with an oil-water interface.
  • the change in contact angle is at least 10°, more preferably at least 30°, even more preferably up to 50° and most preferably up to 70°.
  • the requirement will be to break the emulsion, or to cause phase inversion, quickly, and preferably as quickly as possible.
  • the emulsion is broken, or phase inversion takes place, in less that 1 hour, more preferably less than 15 minutes, even more preferably less than 5 minutes and most preferably less than 1 minute .
  • the particles of the invention may be formed essentially entirely from one or more responsive polymer (s).
  • one responsive polymer forms the particle core whilst another forms the particle shell.
  • the responsive polymer (s) may merely form a shell on an inert particle core or the responsive polymer (s) may form the particle core and be surrounded by a non-responsive (inert) shell. Mixtures of responsive and non-responsive polymers may also be used.
  • the amount of responsive polymer in the particulate emulsifier must be sufficient to make the particle responsive to at least one external condition/stimulus.
  • the particulate emulsifiers used according to the invention are in the size range 1 x 10 "9 to 1 x 10 "5 m, preferably 5 x 10 "8 m to 5 x 10 -6 m.
  • the stability of emulsions that are produced using particulate emulsifiers comprising responsive polymers is dependent on the external environmental conditions . Varying the environmental conditions therefore affects the stability of the emulsion. Any stimulus which is capable of changing one or more environmental condition (s) and hence the hydrophilic/hydrophobic balance of the responsive polymer can be used to break, or cause phase inversion of, the particle-stabilised emulsions according to the invention.
  • Environmental conditions which- may affect the hydrophilic/hydrophobic balance of the responsive polymer include pH, temperature and ionic strength.
  • Preferred stimuli according to the invention therefore include a change in temperature, a change in pH or a change in ionic strength, for example, due to the addition of a suitable salt/electrolyte.
  • the degree and nature of the sensitivity of the particulate emulsifiers to the external condition (s) can be tailored by varying the nature and/or amount of the responsive polymers. For example, by selecting a pH- responsive polymer, it is possible to produce an emulsion the stability of which is pH-dependent .
  • a particular responsive polymer may be responsive to more than one stimulus.
  • the hydrophilic/hydrophobic balance of a particular polymer may depend on both ⁇ the pH and the temperature of its environment.
  • An emulsifier that is sensitive to more than one external condition may therefore be prepared by utilising such a polymer.
  • two or more different responsive polymers may be used, each of which is responsive to a different external stimulus.
  • Demulsification, . or phase inversion, of an emulsion according to the invention may be reversed by reversing the environmental change used to produce demulsification or phase inversion.
  • a change in emulsion pH or temperature for example, is reversible.
  • Some of the stable emulsions according to the invention break down, or invert, when the pH of the emulsion is lowered. . However, if the pH of the broken or inverted emulsion is raised to above the pH at which demulsification or inversion occurred, a stable emulsion may reform. Similarly, demulsification or inversion produced by raising or lowering the emulsion temperature may be reversed by . lowering or raising the temperature, respectively.
  • responsive polymer for use in the particulate emulsifiers of the invention will depend inter alia on which particular stimulus is required to break the emulsion, or cause phase inversion, and on the nature and intended use of the emulsion.
  • Properties of the bulk polymer can be used as a guide for selecting which responsive polymers would be suitable for use in the present invention.
  • polyDMA can be used to ⁇ make particles comprising a polyDMA shell and a polystyrene core which stabilise emulsions above the pKa- of approximately 7 for the polymer conjugate acid but which do not form stable emulsions below this pKa.
  • the responsive polymer used according to the present invention can be any polymer that has a variable hydrophilicity. In other words, any polymer which changes its affinity for water (and conversely, oil) in response to an external stimulus or changing environmental condition (s) .
  • the responsive polymer is not limited by way of polymer architecture.
  • the responsive polymer may therefore comprise a homopolymer or copolymers such as statistical, alternating, graft, star and block copolymers.
  • the responsive polymer may also comprise any number of different comonomers .
  • Preferred responsive polymers for use according to the invention are polymers which display a change in hydrophilic/hydrophobic balance in response to a change in pH, temperature or ionic strength.
  • Polymers which show pH, temperature, or ionic strength sensitivity are well known in the art (see for example, Angew. Chem. Int. Ed., 2001, 40, No. 12, 2328-31; Angew. Chem. Int. Ed., 2002, 41, No. 8, 1413-16; J. Am. Chem. Soc, 1998, 120, 12135-12136; J. Am. Chem. Soc, 2001, 123, 9910-9911; Polymer, 42 (2001), 5993-6008; Macromolecules 1999, 32, 2088-2090; Chem. Commun. , 2002, 2122-2123; and Current Opinion in Colloid & Interface Science 6 (2001) 249-256) , and references cited therein.
  • Water-soluble polymers having inverse temperature solubility behaviour display a lower critical solution temperature (LCST) in aqueous solution. Below the LCST the polymer is hydrophilic but above the LCST the polymer becomes insoluble in water and phase separation occurs. Hence, the hydrophilic/hydrophobic balance of the polymer changes around the LCST.
  • the LCST depends on inter alia the hydrophilicity of the polymer and the polymer molecular weight.
  • Very hydrophilic polymers have a high LCST.
  • the LCST of polyMEMA is around 50°C in the absence of any added salt.
  • Polymers that are less hydrophilic have a lower LCST.
  • the LCST of polyDMA is around 35 to 45°C depending on its molecular weight.
  • Some polymers that are not usually considered to be hydrophilic because they are insoluble in water at room temperature may have an LCST below room temperature and so may become soluble on cooling to below room temperature (e.g. poly (propylene oxide), which has an LCST of around 15°C) .
  • Some polymers have a very sharp transition from water-soluble to water-insoluble as the solution is heated above the polymer LCST, for example poly (JW-isopropylacrylamide) which has an LCST of 32°C in pure water.
  • the responsive polymer may comprise a copolymer comprising a combination of monomers that display inverse temperature dependent solubility.
  • Copolymer compositions can be tailored to provide a polymer that has a particular preferred LCST.
  • a copolymer of A and B would have an LCST that lies between the LCSTs of the homopolymers comprising only A or only B.
  • the LCST of polyDMA homopolymer for example, can potentially be raised by polymerising DMA monomer with PEG 3 soMA, whose homopolymer has an LCST of 90-100°C.
  • the above polymers provide particles with the ability to change hydrophilicity depending on external temperature.
  • Polymers that are only weakly hydrophilic at room temperature will have some affinity for both the oil and water interfaces of emulsions. 5 Particles comprising such polymers will therefore stabilise oil-in-water emulsions at this temperature.
  • the responsive polymer, and hence particle will no longer have affinity for the water phase and the 10 emulsion will therefore break, or invert.
  • 15 pH will generally include any polymers comprising acidic or basic functional groups on the polymer chain.
  • the degree of hydrophilicity of such polymers will depend on the degree of protonation or deprotonation of such functional groups.
  • the functional groups are
  • the responsive polymers suitable for use according to this aspect of the invention are preferably responsive between the range of pH 2 to pH 12, more preferably pH 4 to pH 10.
  • Suitable functional groups include amines and carboxylic acids.
  • polymers are known in the art and include, for example, polymers prepared from ( eth) acrylic acid monomers and derivatives thereof. Particular examples include polyDMA, polyMEMA, polyDEA, polyDPA, poly2-VP, poly4-VP, polyTBA, polyAA and polyMAA.
  • Polymers comprising acidic or basic residues will display different hydrophilicity above and below the. polymer (or conjugate acid) pKa value.
  • PolyDEA and polyDPA for example, which include a tertiary amine group on each
  • 35 monomer residue are substantially water-insoluble above the pKa of the conjugate acid when the amine groups are not protonated, but are highly water soluble below the pKa when the amine groups are protonated and each group carries a positive charge.
  • PolyDMA and polyMEMA for example, which also include a tertiary amine group on each monomer residue, are water-soluble above the pKa of the conjugate acid when the amine residues are not protonated but the hydrophilicity is significantly increased when the amine groups are protonated below the polymer pKa.
  • the stimulus necessary to change the hydrophilicity of such polymers is therefore a change in pH.
  • the pKa value of a polymer or conjugate acid of a polymer indicates the pH at which 50% of the acid groups are deprotonated. Any polymer which has an acidic or basic moiety on each monomer residue comprises a large number of acidic or basic groups.
  • the change in hydrophilicity of such polymers is hot therefore a sharp transition around the polymer pKa as the pH is adjusted around the pKa value. Complete protonation or deprotonation may therefore take place at pH values well above or below the pKa.
  • Figure 1 is a schematic representation of the reversible demulsification or breaking of a pH-responsive oil-in- water emulsion using pH-responsive latex particles according to the invention.
  • Figure 2 is a schematic representation of the phase inversion of a pH-responsive latex emulsion.
  • pH-responsive polymer to incorporate into the ' emulsifier particle used according to the invention will depend on the pH at which the change in hydrophilicity is required.
  • polyDMA for example, the polymer is weakly hydrophilic above the pKa of the conjugate acid when the amine groups are less protonated (around pH 8) and also has affinity for a number of oils such as toluene and (hot) n-hexane.
  • this polymer will adsorb at the oil/water interface for a number of oil and water combinations. Particles comprising this polymer are therefore able to form stable emulsions above the pKa of the polymer conjugate acid.
  • a polymer's water solubility can also be changed by changing the ionic strength of an aqueous solution of the polymer, for example, by adding salt to the aqueous solution, or by diluting or concentrating an aqueous salt solution of the polymer.
  • a number of water-soluble polymers are known to precipitate out of solution when salt is added. Ions from the salt compete for the polymer's hydration layer of water molecules which means that solvation of the polymer is reduced leading to the polymer precipitating out of solution.
  • salt can be used to adjust the water solubility of polymers and can therefore be used as a trigger to break emulsions according to the present invention comprising salt- sensitive polymers.
  • Water-soluble polymers known to ⁇ precipitate out of solution on the addition of salt include poly (ethylene oxide), polyDMA and polyMEMA.
  • the , minimum amount of salt required varies according to the nature of the polymer, with polyMEMA being particularly sensitive to 'salting-out'.
  • Another factor that can play a role is the solution pH: a lower solution pH can require extra salt to cause precipitation, or even prevent precipitation.
  • responsive polymer to use in the emulsifier particles also depends on the type of particle that is to be used as an emulsifier.
  • preferred types of particle include microgels and core- shell particles that include sterically-stabilised latexes, sterically-stabilised inorganic sols and polymer composite particles.
  • the responsive polymer chosen should therefore be amenable to the method of preparation necessary to make the particle of choice.
  • the particle emulsifier comprises a polymeric microgel.
  • Microgels are colloidal particles that are (or can be tuned to become) solvent-swollen.
  • .Microgel particles are cross-linked polymer (usually latex) particles.
  • the polymer chains that form the microgel are solvated, which means that solvent enters the microgel core and the microgel particle is swollen.
  • the cross-links mean that the microgel particle retains its particle structure and does not completely dissolve or disintegrate in the solvent.
  • solvent is excluded from the microgel core and the microgel forms a collapsed compact, latexlike structure.
  • microgels according to this preferred embodiment comprise cross-linked polymer particles wherein at least some of the polymer chains forming the particles comprise a responsive polymer. They can be stabilised in suspension by any means known in the art for stabilising suspending solid particles, for example electrical double layer (charge or surfactant ) stabilisation or steric (polymeric) stabilisation.
  • microgel according to the invention is a charge-stabilised microgel formed from a cross- linked responsive polymer, for example polyDEA
  • An alternative preferred microgel structure comprises a cross-linked responsive polymer core that is sterically- stabilised.
  • steric stabilisation is provided by polymer chains that are different to those forming the microgel core.
  • the steric stabilising layer also comprises a responsive polymer.
  • the steric stabilising layer can comprise non- responsive polymers, however.
  • Suitable responsive polymers include poly (meth) acrylates or (meth) acrylamides, preferably acrylamides or tertiary amine-substituted (meth) acrylates, preferably polyDEA, polyDMA, polyMEMA or polyNIPAM, most preferably polyDMA.
  • Preferred non-responsive steric stabilisers include neutral, water-soluble polymers such as poly(N- vinylpyrrolidone) or, preferably, PPEG 20 ooMA.
  • microgel particles according to the invention include charge-stabilised polyDEA microgels, microgels comprising a polyDEA microgel core stabilised by a polyDMA steric stabilising layer, microgels comprising polyDEA microgel cores stabilised by a chemically grafted PEG 20 ooMA layer and microgels comprising polyDPA microgel cores stabilised by a chemically grafted PEG 20 oo A layer.
  • Suitable polymeric microgels may be made, for example, by emulsion or dispersion polymerisation under conditions that ensure a good solvent environment for the steric stabiliser and a poor/non-solvent environment for the microgel component .
  • the particles of the present invention have a core/shell structure.
  • core is meant an inner region of the particle that is preferably unresponsive to changes in external conditions.
  • the shell comprises a responsive polymer.
  • the shell of these particles can be attached to the core by any means as long as the attachment to the core is sufficiently strong such that little or no disintegration of the particles occurs when they are in use as emulsifiers.
  • the shell can be attached by physical (e.g. adsorption) or chemical (e.g. covalent or ionic bonds) means.
  • such sterically-stabilised latex particles comprise a polymer core surrounded by a responsive polymer "shell" and are therefore suitable for use as emulsifiers in accordance with the present invention.
  • Such particles should be substantially insoluble in either phase of the emulsion.
  • One particularly preferred type of core/shell particle comprises a sterically-stabilised colloidal polymer dispersion, also know as a sterically-stabilised polymer latex, wherein the steric stabiliser preferably comprises a responsive polymer.
  • the composition of the polymer latex core is not particularly limited and can comprise any polymer that can be produced in latex form.
  • Methods well documented in the art for producing sterically-stabilised polymer latexes include emulsion polymerisation and dispersion polymerisation.
  • the polymer particles are generally synthesised via a free-radical initiated mechanism, but other chemistries can also be used, e.g. anionic dispersion polymerisation, or step polymerisation for the synthesis of polyurethane particles. Any monomer or combination of monomers that is amenable to free radical polymerisation may be used to form the latex polymer core.
  • Suitable monomers are typically vinyl monomers, for example styrene and its derivatives, acrylates, methacrylates, dienes, chloroprene, vinyl chloride, vinyl acetate, acrylonitrile, acrylamide and ethylene.
  • Particularly preferred latex cores comprise polystyrene, poly(alkyl methacrylate) or poly(alkyl acrylate) , in particular polystyrene, especially cross-linked polystyrene.
  • the polymer latex core may be cross-linked during synthesis to ensure that the particle core remains insoluble in the dispersed phase of the emulsion when used as an emulsifier.
  • polystyrene is soluble in some oils such as toluene whereas cross-linked polystyrene is insoluble in the same oils.
  • the steric stabiliser of the polymer latex comprises an amphiphilic block copolymer.
  • Amphiphilic block copolymers are well known in the art to stabilise colloidal dispersions.
  • Amphiphilic block copolymers are able to sterically stabilise solid dispersions by adsorbing onto a surface of a dispersed solid such that one block of the copolymer which does not have affinity for the continuous phase adsorbs onto the particle surface to form an anchor, while the other block remains solvated and extends into the dispersion medium to form a steric barrier against flocculation or coagulation.
  • the anchor block may be partially incorporated into the latex core.
  • the block that provides the stabilising layer i.e. the block that extends into the dispersion medium, is a responsive polymer.
  • the composition of the amphiphilic block copolymer stabiliser is not particularly limited.
  • the anchor "block” can comprise any polymer or combination of polymers that is strongly adsorbed to the latex core.
  • pol methyl methacrylate
  • the stabilising "block” can be any responsive polymer amenable to copolymerisation with the anchor block.
  • the block copolymers according to this preferred embodiment are preferably made by (pseudo) living polymerisation techniques known in the art, for example, group transfer polymerisation, living anionic polymerisation, living cationic polymerisation, living radical polymerisation (e.g. ATRP, RAFT, nitroxide- mediated etc.).
  • Preferred responsive polymers according to this embodiment are therefore those that can be copolymerised with an "anchor" block according to known living polymerisation techniques.
  • the monomers that form the anchor block and the responsive block are similar in structure to simplify block copolymer synthesis.
  • the blocks of the amphiphilic copolymer both comprise (meth) acrylates.
  • the anchor block comprises a hydrophobic alkyl methacrylate, for example polyMMA.
  • the stabilising block comprises a functionalised methacrylate, more preferably a tertiary a ine- substituted methacrylate,- preferably polyDMA, polyDEA, polyDPA, polyMEMA.
  • a most preferred block copolymer is polyMMA-block-polyDMA.
  • graft copolymers may also be used as polymer latex steric stabilisers according to the invention.
  • Preferred graft copolymers comprise polymeric
  • combs wherein the backbone is a hydrophobic polymer with hydrophilic polymer "hairs".
  • the hydrophilic hairs comprise a responsive polymer.
  • Preferred responsive polymers are as described above for the block copolymer stabilising block.
  • Preferred graft comb polymers are synthesised from DMA-St macromonomers and styrene and/or MMA. The synthesis of statistical/graft copolymers is well known in the art.
  • Particularly preferred stabilised latex particles according to this embodiment include polystyrene latex particles stabilised with polyMMA-block-polyDMA.
  • stabilisation of the polymer latex is provided by chemically grafting a macromonomer onto the outer surface of the latex particle.
  • Macromonomers are polymers that contain a single, usually terminal polymerisable end group.
  • the use of macromonomers to produce sterically-stabilised latexes is known in the art [D. B. Cairns et al., Langmuir, 1999, vol. 15, pg. 8052 and references therein] .
  • the macromonomer preferably comprises a responsive polymer and a poly erisable end group that can be chemically incorporated into the polymer latex as the latex particles are synthesised.
  • the macromonomer end group can be any end group that is capable of being incorporated into the polymer latex core during latex synthesis.
  • poly (acrylic acid) macromonomers with terminal styrene end groups have been used to stabilised polyMMA latex particles (Polymer 1997, 38, 5471 and Macromol. Rapid Commun. 1997, 18, 639) .
  • the macromonomer preferably comprises a poly (meth) acrylate, more preferably a tertiary amine- substituted (meth) acrylate, preferably polyDEA, polyDMA, polyMEMA, polyDPA etc, most preferably polyDMA.
  • the functional polymerisable group is preferably a styrene residue.
  • the latex particle is a polystyrene latex stabilised by a steric stabilising layer comprising polyDMA-St macromonomers grafted onto the polystyrene particles.
  • Suitable polyDMA-St macromonomers and macromonomer stabilised polystyrene latexes may be prepared according to Lascelles et al. (Macromolecules, 1999, 32, 2462) .
  • Another particularly preferred core-shell particle comprises an inorganic core with a responsive polymer on the -outer surface forming a sterically-stabilising shell;
  • the composition of the inorganic- core is not particularly limited but the core is preferably substantially inert. Suitable examples include commercially available silica, alumina, Fe 2 0 3 , BaS0 4 , CaS0 4 and CaC0 3 sols.
  • the polymer shell may be attached to the core by, for example, surface pre-treatment with a suitable siloxane (see C. Perruchot et al., Langmuir 2001, vol. 17, pg. 4479).
  • the responsive polymer is chemically grafted onto the inorganic core by polymerising the appropriate monomer from initiation sites on the surface of the inorganic particle by ATRP.
  • a polyelectrolytic ATRP macro-initiator is electrostatically adsorbed onto the surface of an anionic silica sol, and the appropriate monomer can be polymerised by ATRP from the macro-initiator.
  • the responsive polymer may be generated from reactive sites on the inorganic particle surface by ATRP.
  • Preferred responsive polymers according to this aspect of the invention are therefore polymers that can be synthesised by ATRP. These include polyDMA, polyDEA, polyMEMA, polyDPA etc.
  • the core comprises silica particles.
  • the responsive shell comprises a poly (meth) acrylate or (meth) acrylamide, preferably a tertiary amine-substituted (meth) acrylate, most preferably polyDEA, polyDMA, polyMEMA, polyDPA etc, most preferably polyDMA.
  • the particles comprise a silica core with polyDMA chains anchored to the surface.
  • Another preferred core-shell particle comprises a composite polymer particle wherein a responsive polymer shell is polymerised around a polymeric particle core.
  • Composite polymer particles are known in the art e.g. M. Okubo et al., Colloid Polym. Sci., 1995, vol. 273,817).
  • Composite particles may be produced by seeded emulsion polymerisation or seeded dispersion polymerisation wherein the component that will form the composite core is the emulsion or dispersion seed and the component that will form the outside composite layer is polymerised around the emulsion/dispersion seed. Seeded emulsion polymerisation and seeded dispersion polymerisation are well known in the art.
  • the particles that ' are used as emulsion or dispersion seeds in the second stage of the polymerisation ' may be themselves produced by emulsion or dispersion polymerisation, respectively.
  • Emulsion polymerisation is preferred since this is a solventless
  • the particle core may be any polymer which can be produced by emulsion polymerisation but preferred cores comprise polymers made from monomers that are relatively inexpensive, robust and readily available, for example styrene and its derivatives, alkyl ethacrylates, alkyl acrylates, vinyl chloride, ethylene and vinyl acetate.
  • the outer layer and/or the core of the composite particle comprises a responsive polymer.
  • the outer layer of the composite comprises a responsive polymer.
  • Particles produced according to this particular embodiment of the invention are especially preferred due to their ease of synthesis, especially on a commercial scale.
  • Preferred polymer composite particles according to the invention comprise a core of polystyrene or polyMMA, preferably polystyrene.
  • the responsive shell preferably comprises a poly (meth) acrylate, or poly (meth) acrylamide, preferably a tertiary amine-substituted (meth) acrylate, or acrylamide, preferably polyDEA, polyDMA, polyMEMA, polyDPA or polyNIPAM, most preferably polyDMA.
  • a most preferred composite particle comprises a polystyrene core surrounded by a polyDMA shell.
  • Suitable polyDMA/polystyrene composite particles may be synthesised in accordance with M. Okubo et al (Colloid Polym. Sci., 1995, vol. 273, pg. 817).
  • PolyNIPAM/polystyrene composite particles may be synthesised in accordance with methods known in the art.
  • the core shell particles of the invention comprise shell cross-linked (SCL) micelles.
  • SCL micelles comprise block copolymer particles with a non-cross-linked core surrounded by a cross-linked shell (corona) .
  • the cross-links prevent dissociation of the block copolymer micelles under conditions when block copolymer micelles would normally be expected to dissociate (e.g. at low block copolymer concentration) .
  • SCL micelles with responsive cores and/or coronas (shells) are known in the art (see for example, J. Am. Chem.
  • SCL micelles comprising responsive polymers known in the art would be suitable for use as particulate emulsifiers according to the present invention.
  • SCL micelles normally have particle diameters of less than 100 nm, for example 20-50 nm.
  • SCL micelles for use according to the invention comprise relatively few cross-links in the micelle corona.
  • SCL micelles may be produced from block copolymer solutions as described in the art.
  • Suitable block copolymers for use according to the invention are able to associate to form micelles in a selective solvent, and also comprise reactive groups in the block which will form the micelle corona to allow corona cross-linking.
  • Either one or both blocks may comprise a responsive polymer.
  • Preferred responsive polymers include polyDMA, polyDEA, polyDPA, polyMEMA and poly (propylene oxide)].
  • Preferred SCL micelles include DMA-MEMA, (OEGMA) DMA-PPO, PEO-DMA-MEMA, PEO-DMA-DEA, DMA-DEA, PEO-GMA-DMA and PEO- GMA-DE .
  • the emulsions produced according to the invention can be oil-in-water or water-in-oil emulsions.
  • the choice of particulate stabiliser will depend on which type of emulsion is to be formed, on the nature of the two phases and on the intended use of the emulsion. Oil-in-water emulsions have gained increasing commercial importance over recent years.
  • the particulate emulsifiers are used to provide stable oil-in-water emulsions that can be controllably, and preferably reversibiy, broken or inverted on application of an external stimulus.
  • the emulsions according to the invention may be used in foods, agrochemicals, cosmetics, personal/home care product formulations, and pharmaceuticals.
  • an oil-in-water emulsion according to the invention may be designed to break .at the surface pH of the human skin, at physiological temperatures and/or upon dilution of the emulsion, such that the oil phase or an ingredient carried by the oil phase is then deposited on contact with (wet) skin or hair.
  • Such emulsions could be used in, for example, shampoos or moisturising compositions, or to deliver active ingredients to the skin.
  • the emulsions of the invention may be useful in pharmaceutical formulations, including topical formulations and formulations for oral drug delivery.
  • an emulsion that breaks at the pH of the human stomach could be used to deliver an active ingredient carried in the dispersed phase to the stomach.
  • the dispersed phase of an emulsion which is stable at the pH of the human stomach but designed to break at the higher pH of the intestines could be used to carry an active ingredient through the stomach for delivery to the intestines.
  • Such emulsions might be particularly suitable for use in the oral delivery of acid-sensitive or acid-labile active -ingredients through the stomach to the intestinal tract.
  • Demulsification of an emulsion according to the invention may also act as a stimulus to cause demulsification of a second emulsion.
  • the dispersed phase of an emulsion according to the invention may carry a stimulus which when released on demulsification in turn causes demulsification of a second emulsion.
  • the droplet size of the emulsions according to the invention is preferably in the range 0.3 to 100 ⁇ m.
  • Other factors that will determine the final emulsion droplet size will be the energy (e.g. stirring rate, time) imparted in generating the emulsion and the concentration of the particulate emulsifier.
  • the emulsions of the invention may comprise additional components in either the oil or the water phase.
  • Additional components are not particularly limited provided that they do not prevent formation of the emulsions or adversely affect emulsion stability.
  • examples include food additives, flavourings, agrochemicals, pharmacologically active ingredients, or cosmetic ingredients (e.g. fragrances) to be delivered to the skin or hair.
  • the present invention provides the use of a particulate emulsifier comprising a sterically- stabilised polymer latex to stabilise an oil-in-water emulsion.
  • a poly [2- (dimethylamino) ethyl methacrylate-block-methyl methacrylate] diblock copolymer was prepared by group transfer polymerisation as described by Baines et al, (Macromolecules, 1996, 29, 3416) .
  • the resulting polymer had a number-average molecular weight of 38,400 g mol -1 and a polydispersity of 1.14, as judged by gel permeation chromatography (tetrahydrofuran (THF) eluant, poly (methyl methacrylate) standards, refractive index detector) .
  • THF tetrahydrofuran
  • X H NMR spectroscopy studies indicated a DMA content of 80 mol% .
  • Emulsion polymerizations were performed in batch mode at °C.
  • a typical synthetic procedure was as follows: t] stabilizer was added to an aqueous solution (adjusted with H ⁇ to pH 3-4) in a three-necked flask (250 ⁇ iL) , fitted with reflux condenser and a magnetic stirrer. This reactii mixture was stirred at room temperature to allow t] stabilizer to dissolve before heating at 70 °C. The flask w, then immersed in an oil bath at the working temperature. Ti reaction mixture was purged with nitrogen and an aqueo' solution of APS (ammonium persulfate) initiator (1.0 wt% bas* on styrene) was added to the reaction vessel.
  • APS ammonium persulfate
  • Ea ⁇ polymerization was allowed to proceed for approximately 24 ' .
  • a typical recipe was as follows: 10.0 itiL of styrene, 0.10 APS initiator and 1.0 g of stabilizer in 90 ml water (s ⁇ Table 1 for stabilizer properties) .
  • the dispersion polymerizations were performed at 60°C in similar manner to the emulsion polymerizations, but with t ' aqueous solution being replaced by either methanol methanol/water mixtures to ensure that the initial reacts solution was homogeneous.
  • the AIBN (2,2 azobisisobutyronitrile) initiator was pre-dissolved in t! styrene monomer and added to the reaction vessel aft degassing with nitrogen.
  • a typical recipe was 'as follow 10.0 mL of styrene, 0.10 g AIBN initiator and 1.0 g stabilizer in 90 mL of either pure methanol or methanol/water mixture (containing either 10 or 30 % water ' . volume). See Table 2 for a summary of reactions.
  • Non pH-responsive sterically-stabilised polystyrene lat (Comparative Example) As a control, a sterically stabilized non-pH-responsiv polystyrene latex (PEGMA/PS) was prepared using monomethoxy capped poly (ethylene glycol) methacrylate (PEGMA) macromonome (10% macromonomer based on styrene monomer) . The experimenta procedure was similar to that described above for the emulsio polymerisation.
  • Latex purification for all latexes
  • Serum replacement (ultrafiltration) was used to eliminat excess stabilizer (and trace monomer, initiator) and henc purify the latex particles.
  • Ultrafiltration was performe using a Molecular/Por ® stirred Spectrum ® cell (400 mL) b replacing the serum with water; this serum was periodicall collected for monitoring.
  • the PEGMA/PS late was purified by centrifugation-redispersion cycles, with eac successive supernatant being decanted and replaced with water
  • the extent of latex purification was assessed b measuring the surface tension of the serum or supernatant respectively; purification was continued until this surfac tension was close to that of pure water (68 to 72 mN ⁇ f 1 ) .
  • Latex Characterization for all polystyrene latexes
  • Table 1 Summary of the architecture type, composition, molecular weight and polydispersity of the 2- (dimethylamino) ethyl methacrylate-based polymeric stabilizers using for the synthesis of pH-responsive latex particles.
  • Mw weight-average molecular weight
  • Mn number-average molecular weight
  • Emulsion polymerizations Polymerisations were carried out at 10 % solids content in a 250 mL round-bottomed flask, fitted with a nitrogen gas inlet, water condenser and an overhead mechanical stirrer working at 250 rpm using a flat anchor type stirrer.
  • the required amount of water (typically 85 g) and a mixture (typically 10.5 g) of DEA (or DPA) and cross-linker monomers were added to the flask and this solution was stirred for half an hour under a nitrogen flow while heating the reaction mixture at 70°C.
  • the reaction was started by adding a previously degassed aqueous solution (typically approximately 5 g) of the initiator (1 wt.% based on monomer).
  • a previously degassed aqueous solution typically approximately 5 g
  • the initiator (1 wt.% based on monomer).
  • ACVA 4' -azobis (4-cyanovaleric acid) initiator
  • SBC sodium bicarbonate
  • the cross-linker used in all microgel syntheses was poly (propylene glycol) diacrylate (PPGDA) (1 wt. % based on monomer) .
  • the required amount (10 wt.% based on monomer) was added to the aqueous solution prior to the addition of the monomer mixture.
  • Latex purification and dynamic light scattering studies we carried out as described in Example 2.
  • Particle diameti measurements vs. pH on selected purified dispersions were mai at 20°C using a Brookhaven instrument equipped with a BI 9000 AT digital autocorrelator and with a solid state las ⁇ (wavelength 532 nm, 125 mW) .
  • the value from the cumula algorithm and second order fit (quadratic) was chose Diluted dispersions of microgel particles were prepared
  • Stock solutions of the dispersions at the desired solid content were prepared by diluting the concentrated dispersions in water.
  • the solution pHs of known volumes (5 mL) of the dilute dispersion were adjusted as required by adding a few drops of concentrated HCl or NaOH solution.
  • the pH of the dispersions was monitored with a pH meter.
  • the dispersions were then homogenised together with 5 mL of the oil using an IKA Ultra-Turrax T-18 basic homogeniser with a 10 mm dispersing tool operating at 6,000 to 12,000 rpm for two minutes.
  • the conductivity of the emulsions immediately after preparation was measured using a digital Conductivity Meter Hanna, model Pri o 5.
  • a measurable conductivity indicated formation of an oil-in-water emulsion, whilst no measurable conductivity indicated formation of a water-in-oil emulsion.
  • the emulsion type was determined by the 'drop, test'.
  • the emulsion droplets were also observed by optical microscopy. A small, dilute sample of the emulsion was put on a microscope slide and viewed with a microscope fitted with a camera. This technique was used to estimate the mean droplet particle size.
  • the emulsion formed from equal volumes of n-dodecane and 2 wt.% of the latex dispersion at pH 8 was a white oil- in-water emulsion which showed no signs of coalescence. Reducing the pH of the dispersion to pH 7 led to limited coalescence. Further lowering of the pH led to increased coalescence and at pH 1.9 practically no emulsion was observed. In all cases an oil-in-water (O/W) emulsion was formed initially at neutral pH (see Table 4) .
  • n-hexadecane and n-amyl acetate as the oil phases no emulsion formation was observed at pH 2 but at pH 7 stable emulsions were observed.
  • the n-hexadecane emulsion was of the oil-in-water type whereas when the oil phase was n-amyl acetate a water-in-oil emulsion was observed. In all cases the pH-responsive character of the latex particles led to demulsification at low pH.
  • the emulsion formed from equal volumes of n-hexadecane and 2 wt.% of the latex dispersion at pH 8.3 was a white oil-in-water emulsion. On reducing the pH of the dispersion to pH 2, no emulsion formation was observed (see Tables 4 and 5) . Again, the pH-responsive character of the latex particles was observed. More stable emulsions were formed if emulsification was carried out using a lower speed of the homogeniser (6,000 rpm).
  • Example 6 (Comparative Example) PEGMA (2 K) /PS latex emulsification
  • the emulsion formed from equal volumes of n-hexadecane and 1 wt.% of the latex dispersion at pHs ranging from 1.9 to 9.2 was invariably a white oil-in- water emulsion.
  • n-amyl acetate as the oil phase at both low pH (4.2) and high pH (9.5) led to the formation of a white water-in-oil emulsion.
  • the particles did not contain any responsive polymers no pH- responsive character was observed and stable emulsions were formed at both low and high pH.
  • Example 7 DEA and DPA microgel latex emulsification
  • the emulsion formed from equal volumes of n-hexadecane and 1 wt.% of the latex dispersion at pH 8 was a white oil-in-water emulsion that showed no signs of coalescence. Reducing the pH of the aqueous' phase of the emulsion to pH 5 led to limited coalescence. Further lowering of the pH led to increased coalescence and at pH 2 practically no emulsion was observed.
  • PEG 2000 MA/DEA microgel latex (PEGMA/DEA)
  • the emulsion formed from equal volumes of n-hexadecane and 1 wt.% of the latex dispersion at pH 2 was very unstable (see Table 7).
  • pH 6.7 a stable oil-in-water emulsion with a small amount of oil separation was formed.
  • pH 10.0 a less stable emulsion is formed.
  • ACVA initiator are responsible for the colloidal stability.
  • PEG ⁇ O QQMA/DPA microgel latex PEGMA/DPA
  • the emulsion formed from equal volumes of n-hexadecane and 1 wt.% of the latex dispersion at pH 2.0 was very stable and of the oil-in-water type. On increasing the pH to 5.5 an oil-in-water emulsion was still formed. At pH 10 an unstable water-in-oil emulsion was apparently formed, as judged by the drop test and. conductivity measurements .
  • Table 8 shows the droplet sizes for a number of different emulsions
  • Sty macromonomer all show similar pH-responsive behaviour, i.e. high surface tension (low surface activity) at ' acidic pH and low surface tension (high surface activity) at alkaline pH. This suggests that the latter three latexes adsorb at the air/water interface at high pH. This pH-modulated surface activity was fully reversible and the adsorption/desorption of the latex particles at the air/water interface is believed to reflect their behaviour at the oil/water interface in the emulsions. These data generally indicate that the pH- responsive emulsifier behaviour of the polystyrene latexes is associated with the character of the steric stabiliser on the outside of the latex particles.
  • Sterically-stabilised polystyrene latex particles were prepared by dispersion polymerisation using a poly[2-
  • Styrene (10.0 ml), azobisisobutyronitrile (AIBN) (100 mg) and the PDMA-PMMA diblock copolymer stabiliser (1.0 g, 10 wt.% based on styrene) were dissolved in 100 ml of a stirred, deoxygenated 70:30 v/v methanol/water mixture at 60 °C.
  • Styrene polymerisation proceeded under nitrogen for 16 h at 60 °C.
  • a stable milky-white polystyrene latex was obtained with a solids content of around 9.2 w/v%, indicating almost complete conversion of the styrene to polystyrene.
  • Serum replacement as described in Example 2 was used to purify the latex particles.
  • the weight-average particle diameter of the latex particles was determined to be 162 ⁇ 20 nm by disc centrifuge photosedimentometry (Brookhaven BI-DCP instrument) . Scanning electron microscopy studies of the dried latex particles also indicated particle diameters in the range 150-180 nm.
  • a 1 H NMR spectrum (CDC1 3 ) of the dissolved polystyrene latex enabled the signals due to the DMA and
  • MMA residues of the stabiliser to be identified at ⁇ 4.2 and ⁇ 3.6, respectively. Comparison of these integrated peaks with those due to the polystyrene indicated a stabiliser content of around 8% by mass.
  • a 2 wt.% stock solution of an aqueous dispersion of the latex according to Example 11 was prepared.
  • the pH of known volumes (2 mL) of this dispersion was adjusted as required by adding a few drops of concentrated acid or base solution.
  • the pH of the dispersions was monitored using a pH electrode.
  • the dispersions were then homogenised together with 2 mL of n-dodecane using a Janke and Kunkel Ultra-Turrax homogeniser with a 10 mm head operating at 11 000 rpm for two minutes.
  • the emulsion type was determined by ' observing whether a drop of the emulsion dispersed readily when added to either water or n-dodecane. All emulsions were equilibrated at 25°C in a thermostatted water bath.
  • the volume-weighted droplet size distributions of some of the emulsions formed were measured by light scattering using a Malvern Mastersizer 2000.
  • the emulsion samples analysed were diluted in water at the pH of the original water phase.
  • the distributions were characterised by the mean diameter and the median diameter (the diameter below which 50 % of the drops were sized) .
  • the emulsion drops were also observed by optical microscopy.
  • a small, dilute sample of the emulsion was added to a haemocytometer cell (Weber Scientific) and viewed with a microscope fitted with a camera.
  • the emulsion formed from equal volumes of n-dodecane and 2 wt.% of the latex dispersion at its natural pH (ea. pH 8) was a white oil-in-water emulsion which showed no signs of coalescence.
  • the median oil drop diameter was about 58 microns.
  • Emulsions formed at low pH (2 to 3) were white oil-in-water emulsions which rapidly began to cream and coalesce after homogenisation of the liquids was halted, whilst at a pH between 7 and 5.5 the emulsions creamed.
  • the pH of the aqueous phase which had separated from an emulsion originally formed at about pH 3 was adjusted to about pH 8 and the phases rehomogenised for one minute.
  • the oils listed in Table 9 was purchased from Aldrich and was used as received.
  • the PDMA-PMMA diblock copolymer was prepared by group transfer polymerization according to the general protocol described by Baines et al Macromolecules, 1996, 29, 3416. Its block composition was confirmed to be approximately 80 mol % by 1 H NMR spectroscopy. Gel permeation chromatography analysis indicated an M n of 38,400 and a M w /M n of 1.14 vs. poly (methyl methacrylate) standards.
  • the PDMA-PMMA diblock copolymer was used to prepare sterically-stabilized polystyrene latex via dispersion polymerization in a 7:3 methanol/water mixture using AIBN initiator as described previously. Purification was achieved using ultrafiltration with periodic replacement of the serum: surface tensiometry was used to confirm that the final latex was not contaminated with non- adsorbed block copolymer stabilizer. 1 H NMR analysis of the resulting latex dissolved in CDC1 3 indicated a PDMA- PMMA stabilizer content of approximately 7 ⁇ 1 wt. %. Scanning electron microscopy studies of the latex particles confirmed their spherical morphology and indicated a particle diameter range of 100-250 nm. This is consistent with both dynamic light scattering and disk centrifuge photosedimentometry studies.
  • 1-Pyrenylmethyl methacrylate was prepared by the reaction of 1-pyrenemethanol (1.0 g) with excess methacryloyl chloride (0.494 g) in dry THF (25 g) for 5 h at 0 °C in the presence of triethylamine (0.87 g) and hydroquinone inhibitor (1 mg) .
  • the resulting reaction was filtered to remove the amine salt and 10 wt. % Na 2 C0 3 aqueous solution was added to neutralize the excess methacryloyl chloride.
  • the 1-pyrenylmethyl methacrylate was extracted with dichloromethane and dried with anhydrous Na 2 S0 4 . This solution was filtered and the dichloromethane was removed under vacuum.
  • Emulsion stabilities after standing for 24 h at room temperature (20-25°C) were assessed by visual observation. In some cases a more accurate emulsion stability assessment was obtained using graduated vessels by monitoring the movement of the oil-emulsion and emulsion- water interfaces with time.
  • the four PS latexes used in this Example are summarized in Table 10.
  • the first entry, SDS-PS is simply a surfactant-stabilized PS latex, whereas the other three examples are sterically-stabilized latexes.
  • a PDMA-PMMA diblock copolymer was used to prepare the DM7-PS latex and also the pyrene-labelled DM6-py-PS latex used for the confocal laser microscopy experiments (here the number within the sample code indicates the PDMA-PMMA stabilizer content of each latex by mass) .
  • the DM2-PS latex was obtained simply by adjusting the purification protocol used to obtain the .
  • Various oil-in-water and water-in-oil emulsions were prepared using a pH-responsive sterically-stabilised polystyrene latex (DM7-PS) .
  • DM7-PS pH-responsive sterically-stabilised polystyrene latex
  • a polydisperse n-dodecane- in-water emulsion was obtained at pH 8.2; these n- dodecane droplets are mainly spherical and disappear on adjusting the solution pH to below pH 3 due to coalescence, since the protonated particulate emulsifier no longer has any affinity for the oil phase.
  • a water- in-1-undecanol emulsion is rather unstable and the droplets are non-spherical, suggesting that partial coalescence has already occurred prior to visual inspection.
  • the PDMA-PMMA stabilizer content of the original sterically-stabilized PS latex (DM7-PS) used in this work was 7 wt. % as judged by 1 H NMR spectroscopy.
  • methanol rather than water
  • methanol is a good solvent for both blocks (PDMA and PMMA) significant copolymer desorption occurs.
  • the final stabilizer content of the methanol-treated latex was only 2 wt. %.
  • Table 13 summarizes the results obtained by systematically reducing the latex concentration from 2.00 % to 0.125 % for two oils.
  • n-dodecane-in-water emulsions prepared at around pH 8.2 there is a clear trend of increasing droplet size and polydispersity at lower latex concentrations, with a concomitant reduction in long-term emulsion stability.
  • water-in-methyl myristate emulsions at approximately the same pH very poor emulsions were obtained at or below latex concentrations of 0.25 %.
  • the latex particles are spherical, with a mean latex diameter of around 130 nm and a relatively narrow particle size distribution.
  • the pyrene content of this latex was estimated to be approximately 1 %, as judged by 1 H NMR spectroscopy.
  • oils of intermediate polarity such as methyl myristate or cineole
  • oil-in-water emulsions formed at pH 8 can become water-in-oil emulsions at pH 2-3, with no demulsification being observed.
  • this inversion only occurs within a narrow volume fraction range (around 0.50 with respect to the oil phase) .
  • the surface concentration of the steric stabilizer is also important in determining the nature of the emulsion, as well as its pH-responsive behavior.
  • Example seeded emulsion copolymerization was used to produce PS/P (DMA-stat-EGDMA) core/shell latex particles for use as pH-responsive . particulate emulsifiers for oil-in-water emulsions.
  • Emulsion polymerization offers a number of advantages (i) unlike dispersion polymerizations, emulsion polymerizations are conducted in purely aqueous media, which is environmentally benign; (ii) free radical polymerization chemistry is facile compared to GTP chemistry (which was required to produce the diblock polymer stabilizer) ; (iii) in principle, a high surface concentration of pH- responsive polymer can be achieved; (iv) a cross-linked pH-responsive shell may be more robust than a merely physically adsorbed diblock copolymer stabilizer.
  • Styrene (S) , DMA and EGDMA (Aldrich) were treated with basic alumina in order to remove inhibitor, and stored at
  • PS/P (D A-stat-EGDMA) particles Seeded emulsion copolymerizations of DMA and EGDMA were performed in the presence of PS seed particles in batch mode at 60 °C (Table 15) .
  • the synthetic procedure was as follows: PS latex (0.893 g; solid content 9.6 wt . %) was added to a solution of Tween 80 (40 mg) , DMA and EGDMA in doubly-distilled water (total water volume, 43 L) at room temperature, and the system was stirred at 250 rpm for 18 h for PS seed particles to be swollen with DMA and EGDMA.
  • the polymerization was started at 60 °C by injecting an aqueous solution of AIBA solution (0.18 g AIBA in 7 ml water) to this stirred system and allowed to proceed for 24 h.
  • AIBA (g> 0.1798 0.1798
  • SEM Scanning electron microscopy
  • Emulsion preparation Emulsions of different volumes of n-dodecane and aqueous latex dispersion containing 1 wt. % of particles were prepared using an Ultra TURRAX R IKA T18 basic (IKA R Works, Inc.) operating at 12,000 rpm for 2 min at 25 °C at either pH 3 or pH 9. The emulsion type was determined via conductivity measurements and using the drop test.
  • the emulsion droplets were observed by optical microscopy (James Swift MP3502, Prior Scientific Instruments Ltd.). A Malvern Mastersizer S instrument was used to determine the mean particle diameter of the droplets.
  • the latex superstructures surrounding the emulsion droplets were observed by SEM after critical point drying (CPD) . CPD was performed with a Polaron E3000 critical point dryer using ethanol. as an intermediate fluid and carbon dioxide as a transitional fluid.
  • Latex characterization For the PS seed latex particles, core-shell PS/P (DMA-stat-EGDMA) latex particles with shell loadings of 10 and 20 wt.
  • the D z values for the 10 wt. % shell latex at . pH 3 and 9 were determined to be 305 and 230 nm, respectively.
  • the P (DMA-sta -EGDMA) shell was highly swollen and expanded at pH 3 due to the high degree of protonation of the cross-linked DMA residues (the pK a of DMA homopolymer is around pH 7.0- 7.5).
  • deprotonation occurred at pH 8 and collapse of the shell layer occurs.
  • n- dodecane-in-water emulsions were obtained after homogenization of 50/50 and 60/40 mixtures of latex and n-dodecane.
  • a polydisperse n-dodecane-in- water emulsion was obtained at pH 8.4 using 20 wt. % shell composite particles after homogenization of a 50/50 mixture of latex and n-dodecane.
  • n-dodecane droplets are mainly spherical and the mean droplet diameter of 63 ⁇ m obtained from Mastersizer data was in good agreement with the optical microscopy images.
  • no emulsions were obtained at pH 3 because the protonated, cationic PDMA shell is too hydrophilic to wet the surface of the oil droplets.
  • PS/P (DMA-stat-EGDMA) core-shell latex particles were successfully prepared from a PS seed latex. These PS . and PS/P (DMA-stat-EGDMA) latexes were characterized in terms of their particle size, morphology and composition using dynamic light scattering, SEM and FT-IR spectroscopy, respectively.
  • PS/P (DMA- stat-EGDMA) latex particles as pH-sensitive particulate emulsifiers, polydisperse n-dodecane-in-water emulsions were prepared at pH 9. The emulsion type and mean droplet diameter were determined by conductivity measurements and optical microscopy.
  • This Example describes the production of Shell Cross- Linked (SCL) Micelles and their use as Stimulus- Responsive Particulate Emulsifiers
  • the PE0 4 5-GMAi8-DEA 3 o triblock copolymer was synthesised using similar conditions to those described in S. Liu, J. V. M. Weaver, M. Save, S. P. Armes, Langmuir, 2002, 18, 8350.
  • a block composition of PE0 5 -GMA 3 o-DEA 50 was targeted, but 1 H NMR studies of the purified copolymer indicated a final block composition of PEO 4 5-GMA ⁇ 8 -DEA 30 suggesting either less than ideal blocking efficiencies or else some fractionation occurred during the purification step.
  • the PE0 5 -Br macro-initiator (4.000 g, 1.9 mmol) and GMA monomer (9.143 g, 57.1 mmol) were added to a reaction flask and were degassed under nitrogen purge for around 30 min. Methanol was degassed separately and 13 mL of this solvent was added to the monomer/initiator mixture via double-tipped needle, followed by a freeze-pump-thaw cycle.
  • Cu(I)Cl (189 mg, 1.9 mmol) catalyst and 2, 2' -bipyridine (594 mg, 3.81- mmol) ligand were introduced into the reaction flask at room temperature to start the polymerisation.
  • the PE0 45 -GMAi8-DEA 3 o triblock copolymer was molecularly dissolved as a 2.0 wt. % solution at pH 2.
  • the solution pH was slowly adjusted to pH 12 using dilute NaOH solution to form well-defined DEA-core micelles. Micellisation was confirmed using DLS, which gave an intensity-average micelle diameter of 26 nm.
  • Shell cross-linking was achieved by adding specific quantities of divinyl sulfone (DVS) to the micellar solution at pH 12 and stirring at room temperature for around 5-6 h at 20 °C.
  • the pH of the SCL micellar solutions was adjusted from pH 12 to approximately pH 9 after DVS cross-linking. Successful shell cross-linking was confirmed by both DLS studies and also using a Polymer Laboratories Particle Size
  • Emulsion stabilities were assessed using optical microscopy after standing for ' at least 24 h at 20 °C.
  • the emulsion type was determined by both conductivity measurements and also by dropping small quantities of the emulsion into both oil and water and observing either homogenisation (continuous phase is the same as the diluent) or droplet stability (dispersed phase is the same as the diluent) .
  • the PEO 45 -GMAi8-DEA 30 triblock copolymer dissolved molecularly in aqueous solution at low pH; on addition of
  • 1 H NMR spectra of the micelles ' and SCL micelles as a function of pH are shown in Figure 4. These micelles comprised • DEA cores, GMA inner shells and PEO outer coronas.
  • OM Optical Microscopy
  • Emulsion type determined via conductivity measurement and drop test.
  • Example 15 clearly shows that the SCL micelles act as a pH-responsive particulate emulsifier.

Abstract

Use of a particulate emulsifier comprising at least one polymer, in an oil-in water or water-in-oil emulsion, wherein the hydrophilic/hydrophobic balance of the polymer can be varied on application of a stimulus to break the emulsion, or to cause phase inversion.

Description

Particulate Emulsifiers , Emulsions and Uses Thereof
The present invention relates to the use of particles as emulsifiers in oil-in-water and water-in-oil emulsions.
Emulsions find application in a wide range of fields, for example food, agrochemicals, cosmetics, personal/home care product formulations, pharmaceuticals, tertiary- oil recovery, etc. Low molar mass surfactants and surface- active polymers are well known as emulsifiers for use in the preparation of emulsions.
A number of disadvantages are associated with the use of small molecule emulsifiers, however. For example, some are irritants to human skin while the breakdown products of others have been shown to cause damage to the environment. For this reason the industrial use of alkyl phenol ethoxylate emulsifiers is now being phased out. Emulsions comprising small molecule emulsifiers can be difficult to formulate reproducibly and are relatively unstable to coalescence of the emulsified droplets.
Fine particles are also known to act as emulsifiers. Emulsions stabilised by fine particles are often referred to in the art as "Pickering" or "Ramsden" emulsions.
Particulate emulsifiers known in the art include hydrophilic silica sols as emulsifiers for oil-in-water emulsions, and charge-stabilised latex particles as emulsifiers for water-in-oil emulsions. For a review of particulate emulsifiers see B.P Binks, Curr. Opin .
Colloid Interface Sci . , 2002, 7, 21. See also US 6428796
As particulate emulsifiers are colloidal rather than molecular in nature they may show lower toxicity and reduced irritancy to human skin compared to small molecule emulsifiers. Emulsions produced using particle- based emulsifiers also tend to be more stable to coalescence and the systems in general are more robust, and are therefore easier to make and reproduce.
Emulsions containing small molecule surfactants are prone to foaming as the emulsion' is being produced. This can cause significant problems when emulsions are produced on an industrial scale and addition of expensive silicon- based anti-foaming agents is often necessary. Particulate emulsifiers do not usually stabilise foams however and therefore very little foam or none at all is produced during formulation.
It is known that a significantly higher amount of energy is required to remove particulate emulsifiers from the emulsion interface compared to small molecule emulsifiers. Hence, particle-stabilised emulsions are significantly more stable to breaking (e.g. demulsification) than small molecule-stabilised emulsions.
It is envisaged that the particulate emulsifiers of the present invention may be recovered from the emulsions of the invention and reused. The particles may be recovered by filtration, centrifugation etc. In contrast, it would be difficult to recover small molecule emulsifiers from an emulsion.
It is often desirable to break emulsions once they are formed, for example, to allow release of an agent carried by one of the phases. This can be difficult to achieve" in a controlled manner, particularly in the case of particle-stabilised emulsions where the emulsifier is strongly adsorbed at the emulsion interface. So-called demulsifiers can be added to break down emulsions. One disadvantage of this method is that the emulsion cannot be reformed once the demulsifier is added to the system. Polymeric emulsifiers with stabilising properties which can be switched on and off are known in the art. Mathur et al. (Nature,. 1998, Vol 392, pp367) have reported soluble copolymers of methacrylic acid and ethylene oxide which stabilise oil-in-water emulsions under acidic conditions when hydrogen bonding interactions causes formation of hydrophobic segments along the polymer chain. An increase in pH disrupts the hydrogen bonding and hence suppresses formation of the hydrophobic sections and leads to the break-up of the emulsion.
Koh et al. ( Chem . Commun . , 2000, 2461) have reported the use of water-soluble poly (N-isopropyl acrylamide) /poly ethylene glycol copolymers for use as thermally responsive emulsifiers. The authors reported reversible gelation of oil-in-water emulsions above the polymer lower critical solution temperature (LCST) .
Neither article teaches the use of particulate emulsifiers, however.
There exists a need for non-toxic, non-irritant emulsions which are non-foaming and highly stable to ' coalescence under normal conditions of use but which can be broken (demulsified) in a controlled manner. In addition, there is a need for emulsions that can be phase inverted in a controlled manner. It is postulated that particulate emulsifiers will be easier and cheaper to synthesise and will' give more robust emulsions than soluble emulsifiers.
Summary of the Invention
In one embodiment, the present invention provides the use of a particulate emulsifier comprising at least one polymer in an oil-in-water or water-in-oil emulsion, wherein the hydrophilic/hydrophobic balance of the polymer can be varied on application of a stimulus to break the emulsion, or to cause phase inversion. Preferably, the breaking, or phase inversion, of the emulsion is reversible.
In a further embodiment, the invention provides the use of a particulate emulsifier comprising at least one responsive polymer, wherein the stability of the emulsion is dependent on at least one environmental condition.
In another embodiment the invention is directed to oil- in-water and water-in-oil emulsions comprising at least one particulate emulsifier comprising a polymer wherein the hydrophilic/hydrophobic balance of the polymer can be varied on application of a stimulus to break the emulsion, or to cause phase inversion.
In another embodiment the invention is directed to oil- in-water and water-in-oil emulsions comprising at least one particulate emulsifier comprising a polymer wherein the stability of the emulsion is dependent on at least one environmental condition.
The invention further provides a method for stabilising an oil-in-water or water-in-oil emulsion comprising the use of a particulate emulsifier comprising a polymer wherein the hydrophilic/hydrophobic balance of the polymer can be varied by application of a stimulus.
In a further embodiment, the invention provides a method for the preparation of an oil-in-water or water-in-oil emulsion, comprising the use of a particulate emulsifier comprising a responsive polymer wherein the stability of the emulsion is dependent on at least one environmental condition. The invention also provides a method of breaking an emulsion comprising a particulate emulsifier comprising at least one polymer, the method comprising applying a stimulus to vary the hydrophilic/hydrophobic balance of the polymer to an extent sufficient to break the emulsion, or to cause phase inversion.
In a further embodiment, the invention also provides a method of breaking an emulsion comprising a particulate emulsifier comprising at least one polymer, the method comprising varying at least one environmental condition to an extent sufficient to break the emulsion, or to cause phase inversion.-
Preferably, the particulate emulsifier is a polymeric microgel or has a core/shell latex structure.
The invention comprises each and every combination of preferred features disclosed herein.
Brief Description of the Drawings
Figure 1 Schematic representation of pH-responsive emulsification/demulsification using a sterically stabilised polymer latex.
Figure 2 Schematic representation of pH-responsive phase inversion using a sterically stabilised polymer latex Figure 3 Air-water surface tension curve against pH for a number of dispersions of latex particles. Figure 4 1H NMR spectra of micelles and shell cross-linked (SCL) micelles as a function of pH.
Detailed description
The following abbreviations are used herein in reference to monomers (and corresponding polymers) .
(P) DMA/ (poly) DMA (poly) [2- (dimethylamino) ethyl methacrylate]
(P)MMA/ (poly)MMA (poly) (methyl methacrylate]
(P)DEA/(poly)DEA (poly) [2- (diethylamino) ethyl methacrylate]
(P)NIPAM/
(poly)NIPAM (poly) (II-isopropylacrylamide)
(P)MEMA/(poly)MEMA (poly) [2- (N-morpholino) ethyl methacrylate]
(P)PEG350MA (poly) [poly (ethylene glycol)35o monomethoxy-capped methacrylate]
(P)PEG2oooMA (poly) [poly (ethylene glycol)20oo monomethoxy-capped methacrylate]
(poly) DMA-St (poly) [2- (dimethylamino) ethyl methacrylate] / styrene macromonomer (with a single polymerisable styrene end group)
(P)MAA/ (poly)MAA ' (poly)methacrylic acid
( P) 2-VP/ (poly) 2-VP (poly) 2-vinylpyridine
(P) 4-VP/ (poly) 4-VP (poly) 4-vinylpyridine
(P) DPA/ (poly) DPA (poly) [2- (diisopropylamino) ethyl methacrylate
(P)TBA/(poly)TBA (poly) [2- ( tert-butylamino) ethyl methacrylate (OEGMA) DMA-PPO poly [methoxy-capped oligo (ethylene glycol) methacrylate-rλIo k-2- (dimethylamino) ethyl methacrylate- locfc-poly (propylene oxide) ]
PEO-DMA-DEA poly [ (ethylene oxide) -Jloc^-2- (dimethylamino) ethyl methacrylate- locJt-2- (diethylamino) methacrylate]
PEO-GMA-DEA poly [ (ethylene oxide) -jblocic-glycerol monomethacrylate-jblocj!-2- (diethylamino) ethyl methacrylate]
DMA-MEMA poly [2- (dimethylamino) ethyl methacrylate-jlocJc-2- (ΪV-morpholino) ethyl methacrylate]
PEO-DMA-MEMA poly [ (ethylene oxide) -block-2 - (dimethylamino) ethyl methacrylate-jlocc-2- (N- morpholino) ethyl methacrylate]
DMA-DEA poly [2- (dimethylamino) ethyl methacrylate-JIoc.fc-2- (diethylamino) methacrylate]
PPGDA poly (propylene glycol) diacrylate
Some of the above-mentioned monomers can be represented by the following structures :
Figure imgf000008_0001
DMA DEA polyDMA-St n is approx 8 n is approx45
Figure imgf000009_0001
An emulsion is a mixture of immiscible liquids wherein one liquid is finely dispersed within the continuous phase of another. Emulsions are generally characterised as oil-in-water emulsions, wherein oil droplets are dispersed in a continuous water phase, or water-in-oil emulsions, wherein water droplets are dispersed in a continuous oil phase.
The emulsifiers used according to the present invention are particles which have variable hydrophilicity or hydrophobicity. In other words, the particles' affinity for water (or, conversely, oil) can be varied by varying at ' least one environmental condition. The stability of emulsions comprising such particles is therefore dependent on the environmental conditions .
Particles are classed as hydrophilic if the contact angle they make with an oil-water interface (measured into the water phase) is less than 90 degrees. Particles are classed as hydrophobic if this contact angle is greater than 90 degrees.
Hydrophilic particles are more hydrophilic if the contact angle approaches zero. Hydrophobic particles are more hydrophobic if the contact angle approaches 180 degrees.
Without wishing to be bound by any particular theory, it is postulated that in order to form stable emulsions the particulate emulsifiers used according to the invention should have some affinity for both the oil and water phases of the emulsion. When the particles have affinity for both phases of the emulsion, the particles adsorb at the oil/water interface of the emulsion forming an adsorbed layer around the dispersed phase that prevents coalescence of the dispersed phase and therefore stabilises the emulsion. When the particles do not have affinity for both of the phases in the emulsion, or have significantly stronger affinity for one of the phases, the particles do not adsorb at the emulsion interface and so do not form a stabilising layer. A stable emulsion in which the particles have affinity for both phases can therefore be broken by changing the hydrophilic/hydrophobic balance of the particle emulsifier such that the particle no longer has affinity for both phases of the emulsion, has a much stronger affinity for one phase of the emulsion relative to the other phase, or even has no affinity for either phase.
In this specification, a stable emulsion is considered to be "broken" on the appearance of a macrophase caused by coalescence of the particles of the disperse phase.
Phase inversion occurs when an oil-in-water emulsion is converted into a water-in-oil emulsion, or vice versa. Phase inversion can occur directly, without the intermediate formation of a macrophase.
The particulate emulsifiers used according to the invention should remain essentially intact in either phase of the emulsion, that is, they should not completely disintegrate in either phase
The particle emulsifiers used in the present invention comprise at least one polymer which displays variable hydrophilicity/hydrophobicity depending on external conditions. The term "responsive polymer" is used herein to describe any polymer whose hydrophilic/hydrophobic balance can be changed by varying one or more external condition (s) .
The polymer may respond to a variation of an external condition by, for example, a steric or conformational change, by a change in protonation or de-protonation, by a change in solvation, by a change in hydration, or by any other response leading to a change in the contact angle of the polymer particle surface with an oil-water interface. Preferably the change in contact angle is at least 10°, more preferably at least 30°, even more preferably up to 50° and most preferably up to 70°.
For many applications the requirement will be to break the emulsion, or to cause phase inversion, quickly, and preferably as quickly as possible. In preferred embodiments of the invention the emulsion is broken, or phase inversion takes place, in less that 1 hour, more preferably less than 15 minutes, even more preferably less than 5 minutes and most preferably less than 1 minute .
The particles of the invention may be formed essentially entirely from one or more responsive polymer (s). In one preferred embodiment one responsive polymer forms the particle core whilst another forms the particle shell. Alternatively, the responsive polymer (s) may merely form a shell on an inert particle core or the responsive polymer (s) may form the particle core and be surrounded by a non-responsive (inert) shell. Mixtures of responsive and non-responsive polymers may also be used.
The amount of responsive polymer in the particulate emulsifier must be sufficient to make the particle responsive to at least one external condition/stimulus. Preferably, the particulate emulsifiers used according to the invention are in the size range 1 x 10"9 to 1 x 10"5 m, preferably 5 x 10"8 m to 5 x 10-6 m.
The stability of emulsions that are produced using particulate emulsifiers comprising responsive polymers is dependent on the external environmental conditions . Varying the environmental conditions therefore affects the stability of the emulsion. Any stimulus which is capable of changing one or more environmental condition (s) and hence the hydrophilic/hydrophobic balance of the responsive polymer can be used to break, or cause phase inversion of, the particle-stabilised emulsions according to the invention. Environmental conditions which- may affect the hydrophilic/hydrophobic balance of the responsive polymer include pH, temperature and ionic strength. Preferred stimuli according to the invention therefore include a change in temperature, a change in pH or a change in ionic strength, for example, due to the addition of a suitable salt/electrolyte.
The degree and nature of the sensitivity of the particulate emulsifiers to the external condition (s) can be tailored by varying the nature and/or amount of the responsive polymers. For example, by selecting a pH- responsive polymer, it is possible to produce an emulsion the stability of which is pH-dependent .
A particular responsive polymer may be responsive to more than one stimulus. For example, the hydrophilic/hydrophobic balance of a particular polymer may depend on both ~ the pH and the temperature of its environment. An emulsifier that is sensitive to more than one external condition may therefore be prepared by utilising such a polymer. Alternatively, two or more different responsive polymers may be used, each of which is responsive to a different external stimulus. Demulsification, . or phase inversion, of an emulsion according to the invention may be reversed by reversing the environmental change used to produce demulsification or phase inversion. A change in emulsion pH or temperature, for example, is reversible. Some of the stable emulsions according to the invention break down, or invert, when the pH of the emulsion is lowered.. However, if the pH of the broken or inverted emulsion is raised to above the pH at which demulsification or inversion occurred, a stable emulsion may reform. Similarly, demulsification or inversion produced by raising or lowering the emulsion temperature may be reversed by . lowering or raising the temperature, respectively.
Responsive polymer
The choice of responsive polymer for use in the particulate emulsifiers of the invention will depend inter alia on which particular stimulus is required to break the emulsion, or cause phase inversion, and on the nature and intended use of the emulsion. Properties of the bulk polymer can be used as a guide for selecting which responsive polymers would be suitable for use in the present invention. For example, polyDMA can be used to ■ make particles comprising a polyDMA shell and a polystyrene core which stabilise emulsions above the pKa- of approximately 7 for the polymer conjugate acid but which do not form stable emulsions below this pKa. It follows that any polymer which has affinity for oil and water at pH values on one side of its pKa value but only affinity for water on the other side is potentially suitable for use as the responsive component in the particulate emulsifiers for use according to the invention. The responsive polymer used according to the present invention can be any polymer that has a variable hydrophilicity. In other words, any polymer which changes its affinity for water (and conversely, oil) in response to an external stimulus or changing environmental condition (s) .
The responsive polymer is not limited by way of polymer architecture. The responsive polymer may therefore comprise a homopolymer or copolymers such as statistical, alternating, graft, star and block copolymers. The responsive polymer may also comprise any number of different comonomers .
Preferred responsive polymers for use according to the invention are polymers which display a change in hydrophilic/hydrophobic balance in response to a change in pH, temperature or ionic strength. Polymers which show pH, temperature, or ionic strength sensitivity are well known in the art (see for example, Angew. Chem. Int. Ed., 2001, 40, No. 12, 2328-31; Angew. Chem. Int. Ed., 2002, 41, No. 8, 1413-16; J. Am. Chem. Soc, 1998, 120, 12135-12136; J. Am. Chem. Soc, 2001, 123, 9910-9911; Polymer, 42 (2001), 5993-6008; Macromolecules 1999, 32, 2088-2090; Chem. Commun. , 2002, 2122-2123; and Current Opinion in Colloid & Interface Science 6 (2001) 249-256) , and references cited therein.
Temperature
Many water-soluble polymers show inverse temperature solubility behaviour in aqueous solution. This means that if a solution of the polymer in water is heated, the polymer becomes less soluble due to a decrease in hydrogen bonding between the polymer and solvent.
Water-soluble polymers having inverse temperature solubility behaviour display a lower critical solution temperature (LCST) in aqueous solution. Below the LCST the polymer is hydrophilic but above the LCST the polymer becomes insoluble in water and phase separation occurs. Hence, the hydrophilic/hydrophobic balance of the polymer changes around the LCST. The LCST depends on inter alia the hydrophilicity of the polymer and the polymer molecular weight.
Very hydrophilic polymers have a high LCST. For example, the LCST of polyMEMA is around 50°C in the absence of any added salt. Polymers that are less hydrophilic have a lower LCST. For example, the LCST of polyDMA is around 35 to 45°C depending on its molecular weight. Some polymers that are not usually considered to be hydrophilic because they are insoluble in water at room temperature, may have an LCST below room temperature and so may become soluble on cooling to below room temperature (e.g. poly (propylene oxide), which has an LCST of around 15°C) . Some polymers have a very sharp transition from water-soluble to water-insoluble as the solution is heated above the polymer LCST, for example poly (JW-isopropylacrylamide) which has an LCST of 32°C in pure water.
The responsive polymer may comprise a copolymer comprising a combination of monomers that display inverse temperature dependent solubility. Copolymer compositions can be tailored to provide a polymer that has a particular preferred LCST. For example, a copolymer of A and B would have an LCST that lies between the LCSTs of the homopolymers comprising only A or only B. Hence, the LCST of polyDMA homopolymer, for example, can potentially be raised by polymerising DMA monomer with PEG3soMA, whose homopolymer has an LCST of 90-100°C.
When incorporated into the particles used, according to the invention, the above polymers provide particles with the ability to change hydrophilicity depending on external temperature. Polymers that are only weakly hydrophilic at room temperature will have some affinity for both the oil and water interfaces of emulsions. 5 Particles comprising such polymers will therefore stabilise oil-in-water emulsions at this temperature. When the emulsion is heated above the polymer LCST, however, the responsive polymer, and hence particle, will no longer have affinity for the water phase and the 10 emulsion will therefore break, or invert.
pH
Polymers that have variable hydrophilicity depending on
15 pH will generally include any polymers comprising acidic or basic functional groups on the polymer chain. The degree of hydrophilicity of such polymers will depend on the degree of protonation or deprotonation of such functional groups. Preferably, the functional groups are
20 either weakly acidic or weakly basic. The responsive polymers suitable for use according to this aspect of the invention are preferably responsive between the range of pH 2 to pH 12, more preferably pH 4 to pH 10. Suitable functional groups include amines and carboxylic acids.
25. Many such polymers are known in the art and include, for example, polymers prepared from ( eth) acrylic acid monomers and derivatives thereof. Particular examples include polyDMA, polyMEMA, polyDEA, polyDPA, poly2-VP, poly4-VP, polyTBA, polyAA and polyMAA.
30
Polymers comprising acidic or basic residues will display different hydrophilicity above and below the. polymer (or conjugate acid) pKa value. PolyDEA and polyDPA, for example, which include a tertiary amine group on each
35 monomer residue, are substantially water-insoluble above the pKa of the conjugate acid when the amine groups are not protonated, but are highly water soluble below the pKa when the amine groups are protonated and each group carries a positive charge. PolyDMA and polyMEMA, for example, which also include a tertiary amine group on each monomer residue, are water-soluble above the pKa of the conjugate acid when the amine residues are not protonated but the hydrophilicity is significantly increased when the amine groups are protonated below the polymer pKa.
The stimulus necessary to change the hydrophilicity of such polymers is therefore a change in pH. The pKa value of a polymer or conjugate acid of a polymer indicates the pH at which 50% of the acid groups are deprotonated. Any polymer which has an acidic or basic moiety on each monomer residue comprises a large number of acidic or basic groups. The change in hydrophilicity of such polymers is hot therefore a sharp transition around the polymer pKa as the pH is adjusted around the pKa value. Complete protonation or deprotonation may therefore take place at pH values well above or below the pKa.
The number and nature of the acidic and/or basic functional groups can be varied to vary the degree of pH responsiveness and the pH value at which breaking or inversion of a particular emulsion will occur. Figure 1 is a schematic representation of the reversible demulsification or breaking of a pH-responsive oil-in- water emulsion using pH-responsive latex particles according to the invention. Figure 2 is a schematic representation of the phase inversion of a pH-responsive latex emulsion.
The choice of pH-responsive polymer to incorporate into the ' emulsifier particle used according to the invention will depend on the pH at which the change in hydrophilicity is required. In the case of polyDMA, for example, the polymer is weakly hydrophilic above the pKa of the conjugate acid when the amine groups are less protonated (around pH 8) and also has affinity for a number of oils such as toluene and (hot) n-hexane. Hence, this polymer will adsorb at the oil/water interface for a number of oil and water combinations. Particles comprising this polymer are therefore able to form stable emulsions above the pKa of the polymer conjugate acid.
Below the pKa when the polymer is fully protonated, however, the polymer has no affinity for oil and does not therefore adsorb at the oil/water interface of an emulsion. Hence, a stable emulsion comprising this polymer at pH 8 can be broken by lowering the pH to the point where the polymer chain is highly protonated
(typically about pH 4) .
Ionic Strength
A polymer's water solubility can also be changed by changing the ionic strength of an aqueous solution of the polymer, for example, by adding salt to the aqueous solution, or by diluting or concentrating an aqueous salt solution of the polymer. A number of water-soluble polymers are known to precipitate out of solution when salt is added. Ions from the salt compete for the polymer's hydration layer of water molecules which means that solvation of the polymer is reduced leading to the polymer precipitating out of solution. Hence, salt can be used to adjust the water solubility of polymers and can therefore be used as a trigger to break emulsions according to the present invention comprising salt- sensitive polymers. Water-soluble polymers known to ■ precipitate out of solution on the addition of salt include poly (ethylene oxide), polyDMA and polyMEMA. The , minimum amount of salt required varies according to the nature of the polymer, with polyMEMA being particularly sensitive to 'salting-out'. Another factor that can play a role is the solution pH: a lower solution pH can require extra salt to cause precipitation, or even prevent precipitation.
The choice of responsive polymer to use in the emulsifier particles according to an embodiment of the invention also depends on the type of particle that is to be used as an emulsifier. As described in more detail below, preferred types of particle include microgels and core- shell particles that include sterically-stabilised latexes, sterically-stabilised inorganic sols and polymer composite particles. The responsive polymer chosen should therefore be amenable to the method of preparation necessary to make the particle of choice.
Microgels
In one preferred embodiment of the invention, the particle emulsifier comprises a polymeric microgel.
Microgels are colloidal particles that are (or can be tuned to become) solvent-swollen. .Microgel particles are cross-linked polymer (usually latex) particles. In a good solvent the polymer chains that form the microgel are solvated, which means that solvent enters the microgel core and the microgel particle is swollen. Even when fully solvated, the cross-links mean that the microgel particle retains its particle structure and does not completely dissolve or disintegrate in the solvent. In poor solvents, solvent is excluded from the microgel core and the microgel forms a collapsed compact, latexlike structure.
The microgels according to this preferred embodiment comprise cross-linked polymer particles wherein at least some of the polymer chains forming the particles comprise a responsive polymer. They can be stabilised in suspension by any means known in the art for stabilising suspending solid particles, for example electrical double layer (charge or surfactant ) stabilisation or steric (polymeric) stabilisation.
One preferred type of microgel according to the invention is a charge-stabilised microgel formed from a cross- linked responsive polymer, for example polyDEA
An alternative preferred microgel structure comprises a cross-linked responsive polymer core that is sterically- stabilised. Preferably, steric stabilisation is provided by polymer chains that are different to those forming the microgel core. In one particularly preferred embodiment, the steric stabilising layer also comprises a responsive polymer. The steric stabilising layer can comprise non- responsive polymers, however.
Suitable responsive polymers include poly (meth) acrylates or (meth) acrylamides, preferably acrylamides or tertiary amine-substituted (meth) acrylates, preferably polyDEA, polyDMA, polyMEMA or polyNIPAM, most preferably polyDMA. Preferred non-responsive steric stabilisers include neutral, water-soluble polymers such as poly(N- vinylpyrrolidone) or, preferably, PPEG20ooMA.
Most preferred microgel particles according to the invention include charge-stabilised polyDEA microgels, microgels comprising a polyDEA microgel core stabilised by a polyDMA steric stabilising layer, microgels comprising polyDEA microgel cores stabilised by a chemically grafted PEG20ooMA layer and microgels comprising polyDPA microgel cores stabilised by a chemically grafted PEG20oo A layer.
Suitable polymeric microgels may be made, for example, by emulsion or dispersion polymerisation under conditions that ensure a good solvent environment for the steric stabiliser and a poor/non-solvent environment for the microgel component .
Core/shell particles
In another preferred embodiment the particles of the present invention have a core/shell structure. By core is meant an inner region of the particle that is preferably unresponsive to changes in external conditions. Preferably the shell comprises a responsive polymer. The shell of these particles can be attached to the core by any means as long as the attachment to the core is sufficiently strong such that little or no disintegration of the particles occurs when they are in use as emulsifiers. The shell can be attached by physical (e.g. adsorption) or chemical (e.g. covalent or ionic bonds) means.
By providing either a physically adsorbed or chemically grafted stabilising layer comprising a responsive polymer, such sterically-stabilised latex particles comprise a polymer core surrounded by a responsive polymer "shell" and are therefore suitable for use as emulsifiers in accordance with the present invention. Such particles should be substantially insoluble in either phase of the emulsion.
Polymer latexes
One particularly preferred type of core/shell particle comprises a sterically-stabilised colloidal polymer dispersion, also know as a sterically-stabilised polymer latex, wherein the steric stabiliser preferably comprises a responsive polymer.
The composition of the polymer latex core is not particularly limited and can comprise any polymer that can be produced in latex form. Methods well documented in the art for producing sterically-stabilised polymer latexes include emulsion polymerisation and dispersion polymerisation. The polymer particles are generally synthesised via a free-radical initiated mechanism, but other chemistries can also be used, e.g. anionic dispersion polymerisation, or step polymerisation for the synthesis of polyurethane particles. Any monomer or combination of monomers that is amenable to free radical polymerisation may be used to form the latex polymer core. Suitable monomers are typically vinyl monomers, for example styrene and its derivatives, acrylates, methacrylates, dienes, chloroprene, vinyl chloride, vinyl acetate, acrylonitrile, acrylamide and ethylene. Particularly preferred latex cores comprise polystyrene, poly(alkyl methacrylate) or poly(alkyl acrylate) , in particular polystyrene, especially cross-linked polystyrene.
The polymer latex core may be cross-linked during synthesis to ensure that the particle core remains insoluble in the dispersed phase of the emulsion when used as an emulsifier. For example, polystyrene is soluble in some oils such as toluene whereas cross-linked polystyrene is insoluble in the same oils.
Block copolymer stabilisers
Preferably the steric stabiliser of the polymer latex comprises an amphiphilic block copolymer. Amphiphilic block copolymers are well known in the art to stabilise colloidal dispersions. Amphiphilic block copolymers are able to sterically stabilise solid dispersions by adsorbing onto a surface of a dispersed solid such that one block of the copolymer which does not have affinity for the continuous phase adsorbs onto the particle surface to form an anchor, while the other block remains solvated and extends into the dispersion medium to form a steric barrier against flocculation or coagulation. If the sterically-stabilised latex particles are produced by dispersion or emulsion polymerisation, the anchor block may be partially incorporated into the latex core. According to this preferred embodiment of the invention, the block that provides the stabilising layer, i.e. the block that extends into the dispersion medium, is a responsive polymer.
The composition of the amphiphilic block copolymer stabiliser is not particularly limited. The anchor "block" can comprise any polymer or combination of polymers that is strongly adsorbed to the latex core. As an example, for a polystyrene latex produced by dispersion polymerisation in alcoholic media, pol (methyl methacrylate) would be a suitable anchor block for the steric stabilising block copolymer layer. The stabilising "block" can be any responsive polymer amenable to copolymerisation with the anchor block.
The block copolymers according to this preferred embodiment are preferably made by (pseudo) living polymerisation techniques known in the art, for example, group transfer polymerisation, living anionic polymerisation, living cationic polymerisation, living radical polymerisation (e.g. ATRP, RAFT, nitroxide- mediated etc.). Preferred responsive polymers according to this embodiment are therefore those that can be copolymerised with an "anchor" block according to known living polymerisation techniques.
Preferably the monomers that form the anchor block and the responsive block are similar in structure to simplify block copolymer synthesis. Preferably, the blocks of the amphiphilic copolymer both comprise (meth) acrylates. Most preferably the anchor block comprises a hydrophobic alkyl methacrylate, for example polyMMA. Preferably the stabilising block comprises a functionalised methacrylate, more preferably a tertiary a ine- substituted methacrylate,- preferably polyDMA, polyDEA, polyDPA, polyMEMA. A most preferred block copolymer is polyMMA-block-polyDMA.
Statistical and/or graft copolymers may also be used as polymer latex steric stabilisers according to the invention. Preferred graft copolymers comprise polymeric
"combs" wherein the backbone is a hydrophobic polymer with hydrophilic polymer "hairs". Preferably, the hydrophilic hairs comprise a responsive polymer. Preferred responsive polymers are as described above for the block copolymer stabilising block. Preferred graft comb polymers are synthesised from DMA-St macromonomers and styrene and/or MMA. The synthesis of statistical/graft copolymers is well known in the art.
Particularly preferred stabilised latex particles according to this embodiment include polystyrene latex particles stabilised with polyMMA-block-polyDMA.
Macromonomer stabiliser
In another preferred type of sterically-stabilised polymer latex according to the invention, stabilisation of the polymer latex is provided by chemically grafting a macromonomer onto the outer surface of the latex particle. Macromonomers are polymers that contain a single, usually terminal polymerisable end group. The use of macromonomers to produce sterically-stabilised latexes is known in the art [D. B. Cairns et al., Langmuir, 1999, vol. 15, pg. 8052 and references therein] . In this preferred embodiment, the macromonomer preferably comprises a responsive polymer and a poly erisable end group that can be chemically incorporated into the polymer latex as the latex particles are synthesised. The macromonomer end group can be any end group that is capable of being incorporated into the polymer latex core during latex synthesis. For example, poly (acrylic acid) macromonomers with terminal styrene end groups have been used to stabilised polyMMA latex particles (Polymer 1997, 38, 5471 and Macromol. Rapid Commun. 1997, 18, 639) .
The macromonomer preferably comprises a poly (meth) acrylate, more preferably a tertiary amine- substituted (meth) acrylate, preferably polyDEA, polyDMA, polyMEMA, polyDPA etc, most preferably polyDMA. The functional polymerisable group is preferably a styrene residue. Most preferably the latex particle is a polystyrene latex stabilised by a steric stabilising layer comprising polyDMA-St macromonomers grafted onto the polystyrene particles.
Suitable polyDMA-St macromonomers and macromonomer stabilised polystyrene latexes may be prepared according to Lascelles et al. (Macromolecules, 1999, 32, 2462) .
Inorganic core shell particles
Another particularly preferred core-shell particle comprises an inorganic core with a responsive polymer on the -outer surface forming a sterically-stabilising shell; The composition of the inorganic- core is not particularly limited but the core is preferably substantially inert. Suitable examples include commercially available silica, alumina, Fe203, BaS04, CaS04 and CaC03 sols. The polymer shell may be attached to the core by, for example, surface pre-treatment with a suitable siloxane (see C. Perruchot et al., Langmuir 2001, vol. 17, pg. 4479). The responsive polymer is chemically grafted onto the inorganic core by polymerising the appropriate monomer from initiation sites on the surface of the inorganic particle by ATRP.
It is also possible to polymerise a monomer around the inorganic core without having any covalent attachment to the core. A polyelectrolytic ATRP macro-initiator is electrostatically adsorbed onto the surface of an anionic silica sol, and the appropriate monomer can be polymerised by ATRP from the macro-initiator. (X. Chen and S. P. Armes Advanced Materials, 2003, vol. 15, 1558 and X. Chen et al., Langmuir, 2004, vol. 20, 587.
The responsive polymer may be generated from reactive sites on the inorganic particle surface by ATRP. Preferred responsive polymers according to this aspect of the invention are therefore polymers that can be synthesised by ATRP. These include polyDMA, polyDEA, polyMEMA, polyDPA etc.
Preferably the core comprises silica particles. Preferably the responsive shell comprises a poly (meth) acrylate or (meth) acrylamide, preferably a tertiary amine-substituted (meth) acrylate, most preferably polyDEA, polyDMA, polyMEMA, polyDPA etc, most preferably polyDMA. In a most preferred embodiment the particles comprise a silica core with polyDMA chains anchored to the surface.
Composite core-shell particles
Another preferred core-shell particle comprises a composite polymer particle wherein a responsive polymer shell is polymerised around a polymeric particle core. Composite polymer particles are known in the art e.g. M. Okubo et al., Colloid Polym. Sci., 1995, vol. 273,817). Composite particles may be produced by seeded emulsion polymerisation or seeded dispersion polymerisation wherein the component that will form the composite core is the emulsion or dispersion seed and the component that will form the outside composite layer is polymerised around the emulsion/dispersion seed. Seeded emulsion polymerisation and seeded dispersion polymerisation are well known in the art. The particles that 'are used as emulsion or dispersion seeds in the second stage of the polymerisation' may be themselves produced by emulsion or dispersion polymerisation, respectively. Emulsion polymerisation is preferred since this is a solventless
(i.e. all-aqueous) synthesis.
For use according to this preferred embodiment of the present invention, the particle core may be any polymer which can be produced by emulsion polymerisation but preferred cores comprise polymers made from monomers that are relatively inexpensive, robust and readily available, for example styrene and its derivatives, alkyl ethacrylates, alkyl acrylates, vinyl chloride, ethylene and vinyl acetate. The outer layer and/or the core of the composite particle comprises a responsive polymer. Preferably, the outer layer of the composite comprises a responsive polymer. Particles produced according to this particular embodiment of the invention are especially preferred due to their ease of synthesis, especially on a commercial scale.
Preferred polymer composite particles according to the invention comprise a core of polystyrene or polyMMA, preferably polystyrene. The responsive shell preferably comprises a poly (meth) acrylate, or poly (meth) acrylamide, preferably a tertiary amine-substituted (meth) acrylate, or acrylamide, preferably polyDEA, polyDMA, polyMEMA, polyDPA or polyNIPAM, most preferably polyDMA. A most preferred composite particle comprises a polystyrene core surrounded by a polyDMA shell. Suitable polyDMA/polystyrene composite particles may be synthesised in accordance with M. Okubo et al (Colloid Polym. Sci., 1995, vol. 273, pg. 817). PolyNIPAM/polystyrene composite particles may be synthesised in accordance with methods known in the art.
Shell cross-linked (SCL) micelles
In another preferred embodiment, the core shell particles of the invention comprise shell cross-linked (SCL) micelles. SCL micelles comprise block copolymer particles with a non-cross-linked core surrounded by a cross-linked shell (corona) . The cross-links prevent dissociation of the block copolymer micelles under conditions when block copolymer micelles would normally be expected to dissociate (e.g. at low block copolymer concentration) . SCL micelles with responsive cores and/or coronas (shells) are known in the art (see for example, J. Am. Chem. Soc, 2001, 123, 9910-11; Macromolecules, 2002, 35, 6121-31; Macromolecules, 2000, 33, 1, 1-3; Langmuir 2002, 18, 8350-7 and V. Butun, PhD Thesis, University of Sussex, 1999) .
It is postulated that the SCL micelles comprising responsive polymers known in the art would be suitable for use as particulate emulsifiers according to the present invention. SCL micelles normally have particle diameters of less than 100 nm, for example 20-50 nm.
Preferred SCL micelles for use according to the invention comprise relatively few cross-links in the micelle corona. SCL micelles may be produced from block copolymer solutions as described in the art. Suitable block copolymers for use according to the invention are able to associate to form micelles in a selective solvent, and also comprise reactive groups in the block which will form the micelle corona to allow corona cross-linking. Either one or both blocks may comprise a responsive polymer. Preferred responsive polymers include polyDMA, polyDEA, polyDPA, polyMEMA and poly (propylene oxide)]. Preferred SCL micelles include DMA-MEMA, (OEGMA) DMA-PPO, PEO-DMA-MEMA, PEO-DMA-DEA, DMA-DEA, PEO-GMA-DMA and PEO- GMA-DE .
The emulsions produced according to the invention can be oil-in-water or water-in-oil emulsions. The choice of particulate stabiliser will depend on which type of emulsion is to be formed, on the nature of the two phases and on the intended use of the emulsion. Oil-in-water emulsions have gained increasing commercial importance over recent years. Hence, in a preferred embodiment of the present invention, the particulate emulsifiers are used to provide stable oil-in-water emulsions that can be controllably, and preferably reversibiy, broken or inverted on application of an external stimulus.
The emulsions according to the invention may be used in foods, agrochemicals, cosmetics, personal/home care product formulations, and pharmaceuticals. For example, an oil-in-water emulsion according to the invention may be designed to break .at the surface pH of the human skin, at physiological temperatures and/or upon dilution of the emulsion, such that the oil phase or an ingredient carried by the oil phase is then deposited on contact with (wet) skin or hair. Such emulsions could be used in, for example, shampoos or moisturising compositions, or to deliver active ingredients to the skin.
The emulsions of the invention may be useful in pharmaceutical formulations, including topical formulations and formulations for oral drug delivery. For example, an emulsion that breaks at the pH of the human stomach could be used to deliver an active ingredient carried in the dispersed phase to the stomach. Alternatively, the dispersed phase of an emulsion which is stable at the pH of the human stomach but designed to break at the higher pH of the intestines could be used to carry an active ingredient through the stomach for delivery to the intestines. Such emulsions might be particularly suitable for use in the oral delivery of acid-sensitive or acid-labile active -ingredients through the stomach to the intestinal tract.
Demulsification of an emulsion according to the invention may also act as a stimulus to cause demulsification of a second emulsion. For example, the dispersed phase of an emulsion according to the invention may carry a stimulus which when released on demulsification in turn causes demulsification of a second emulsion.
The droplet size of the emulsions according to the invention is preferably in the range 0.3 to 100 μm. In general, the smaller the size of the particulate emulsifier, the smaller the droplet size in the emulsion. Other factors that will determine the final emulsion droplet size will be the energy (e.g. stirring rate, time) imparted in generating the emulsion and the concentration of the particulate emulsifier.
The emulsions of the invention may comprise additional components in either the oil or the water phase.
Additional components are not particularly limited provided that they do not prevent formation of the emulsions or adversely affect emulsion stability. Examples include food additives, flavourings, agrochemicals, pharmacologically active ingredients, or cosmetic ingredients (e.g. fragrances) to be delivered to the skin or hair.
In another embodiment, the present invention provides the use of a particulate emulsifier comprising a sterically- stabilised polymer latex to stabilise an oil-in-water emulsion.
The following non-limiting Examples further illustrate the invention.
Example 1
Synthesis of PDMA-block-PMMA copolymer
A poly [2- (dimethylamino) ethyl methacrylate-block-methyl methacrylate] diblock copolymer was prepared by group transfer polymerisation as described by Baines et al, (Macromolecules, 1996, 29, 3416) . The resulting polymer had a number-average molecular weight of 38,400 g mol-1 and a polydispersity of 1.14, as judged by gel permeation chromatography (tetrahydrofuran (THF) eluant, poly (methyl methacrylate) standards, refractive index detector) . XH NMR spectroscopy studies indicated a DMA content of 80 mol% .
Example 2 Synthesis of Sterically-stabilized Polystyrene Latex Particl using Cationic Block Copolymers and Macromonomers
Styrene (purchased from Aldrich) was treated with bas alumina in order to remove inhibitor. Monomethoxy-capp poly (ethylene glycol) methacrylate (PEGMA) macromonomer (Mn
2000) was supplied by Laporte as a 50 wt % aqueous solutio Doubly-distilled de-ionized water was used in all tl polymerizations .
Polystyrene Latex Syntheses Emulsion polymerizations
Emulsion polymerizations were performed in batch mode at °C. A typical synthetic procedure was as follows: t] stabilizer was added to an aqueous solution (adjusted with H< to pH 3-4) in a three-necked flask (250 πiL) , fitted with reflux condenser and a magnetic stirrer. This reactii mixture was stirred at room temperature to allow t] stabilizer to dissolve before heating at 70 °C. The flask w, then immersed in an oil bath at the working temperature. Ti reaction mixture was purged with nitrogen and an aqueo' solution of APS (ammonium persulfate) initiator (1.0 wt% bas* on styrene) was added to the reaction vessel. Ea< polymerization was allowed to proceed for approximately 24 '. A typical recipe was as follows: 10.0 itiL of styrene, 0.10 APS initiator and 1.0 g of stabilizer in 90 ml water (s< Table 1 for stabilizer properties) .
Dispersion polymerizations ■
The dispersion polymerizations were performed at 60°C in similar manner to the emulsion polymerizations, but with t' aqueous solution being replaced by either methanol methanol/water mixtures to ensure that the initial reacts solution was homogeneous. The AIBN (2,2 azobisisobutyronitrile) initiator was pre-dissolved in t! styrene monomer and added to the reaction vessel aft degassing with nitrogen. A typical recipe was 'as follow 10.0 mL of styrene, 0.10 g AIBN initiator and 1.0 g stabilizer in 90 mL of either pure methanol or methanol/water mixture (containing either 10 or 30 % water '. volume). See Table 2 for a summary of reactions.
Non pH-responsive sterically-stabilised polystyrene lat (Comparative Example) As a control, a sterically stabilized non-pH-responsiv polystyrene latex (PEGMA/PS) was prepared using monomethoxy capped poly (ethylene glycol) methacrylate (PEGMA) macromonome (10% macromonomer based on styrene monomer) . The experimenta procedure was similar to that described above for the emulsio polymerisation.
Latex purification (for all latexes) Serum replacement (ultrafiltration) was used to eliminat excess stabilizer (and trace monomer, initiator) and henc purify the latex particles. Ultrafiltration was performe using a Molecular/Por® stirred Spectrum® cell (400 mL) b replacing the serum with water; this serum was periodicall collected for monitoring. Exceptionally, the PEGMA/PS late was purified by centrifugation-redispersion cycles, with eac successive supernatant being decanted and replaced with water In all cases the extent of latex purification was assessed b measuring the surface tension of the serum or supernatant respectively; purification was continued until this surfac tension was close to that of pure water (68 to 72 mNπf1) .
Latex Characterization (for all polystyrene latexes)
Dynamic light scattering studies. Measurements were made a 25°C using a Malvern 4700 instrument equipped with an argon ic laser operating at a wavelength of 488 nm and 30 W. Th scattered light was detected at 90° and the intensity-averag particle diameter was calculated from the particle diffusic coefficient using the Stokes-Einstein equation for dilute non-interacting, monodisperse spheres.
1H NMR spectroscopy. The polystyrene latexes were dissolved i CDCI3 and NMR their spectra recorded. The integrated intensit of the relatively weak signal at δ 4.0 due to the tw oxymethylene protons adjacent to the ester group of the D3Y residues was compared to the five aromatic protons due to th styrene residues at δ 6-8 in order to estimate the DMA-base stabilizer contents of the latex particles. For estimatii the stabilizer content of the PEGMA/PS latex, the signal a about 3.5 ppm due to oxyethylene protons from the -(CH2-CH20) groups was used. This gave a PEGMA content of 9.0 wt . % .
Table 1. Summary of the architecture type, composition, molecular weight and polydispersity of the 2- (dimethylamino) ethyl methacrylate-based polymeric stabilizers using for the synthesis of pH-responsive latex particles.
Figure imgf000034_0001
Mw = weight-average molecular weight Mn = number-average molecular weight
Table 2. Summary of the synthesis conditions, stabilizer typ« mean particle diameters and stabilizer contents of tl polystyrene latexes used in the pH-responsive partic! emulsifiers study.
Figure imgf000034_0002
Figure imgf000035_0001
Dw = weight average diameter
Example 3
Synthesis of 2- (diethylamino) ethyl methacrylate (DEA) and 2- (diisopropylamino) ethyl methacrylate (DPA) microgels .
2- (Diethylamino) ethyl methacrylate (DEA) (Aldrich), poly (propylene glycol) diacrylate (PPGDA) (Aldrich) and 2- (diisopropylamino) ethyl methacrylate (DPA) (Scientific
Polymer- Products) , were treated with basic alumina in order to remove inhibitor. Monomethoxy-capped poly (ethylene glycol) methacrylate (PEGMA) macromonomer
(Mn = 2,000) was supplied by Laporte as a 50 wt % aqueous solution. DMA-Sty macromonomer (degree of polymerisation = 50) was prepared via oxyanionic polymerisation according to the procedure previously described by Lascelles and co-workers (Macromolecules, 1999, 32, 2462) . Doubly-distilled de-ionized water was used in all the polymerisations.
Emulsion polymerizations Polymerisations were carried out at 10 % solids content in a 250 mL round-bottomed flask, fitted with a nitrogen gas inlet, water condenser and an overhead mechanical stirrer working at 250 rpm using a flat anchor type stirrer. For batch reactions and using ammonium persulfate initiator, the required amount of water (typically 85 g) and a mixture (typically 10.5 g) of DEA (or DPA) and cross-linker monomers were added to the flask and this solution was stirred for half an hour under a nitrogen flow while heating the reaction mixture at 70°C. The reaction was started by adding a previously degassed aqueous solution (typically approximately 5 g) of the initiator (1 wt.% based on monomer). In batch reactions using 4, 4' -azobis (4-cyanovaleric acid) initiator (ACVA) an aqueous solution of sodium bicarbonate (SBC) was used to aid its dissolution.
The cross-linker used in all microgel syntheses was poly (propylene glycol) diacrylate (PPGDA) (1 wt. % based on monomer) .
Figure imgf000036_0001
Poly (propylene glycol) diacrylate (PPGDA)
When a reactive macromonomer stabiliser was used, the required amount (10 wt.% based on monomer) was added to the aqueous solution prior to the addition of the monomer mixture.
- The following stabilisers were used in some syntheses to improve colloidal stability:
1. Sodium dodecyl sulphate (SDS) (1.5 wt.% as sole surfactant or 1 wt.% as a co-surfactant, both based on monomer) . 2. Monomethoxy-capped poly (ethylene glycol) methacrylate (PEG2000MA) macromonomer (PEGMA)
3. Styrene-capped DMA macromonomer (polyDMA-St with n=50) .
For the synthesis of DEA latex using the DMAs0-Sty stabiliser, monomer-starved reaction conditions were used. The reaction was carried out at 25°C using a APS/ N,N,N' ,N' -tetramethylethylenediamine (TEMED) redox initiator at pH 8-9. A mixture of DEA/PPGDA/TEMED was fed into an aqueous solution of SDS/APS over a 4 h period. The stirring rate was 180 rpm. In all cases, the contents of the flask turned milky-white within 5-10 min and the reaction mixture was stirred for 16 to 20 h under a nitrogen atmosphere. All other microgel syntheses were conducted at 70°C using either ACVA or APS initiators at pH 8-9.
Latex purification and dynamic light scattering studies we carried out as described in Example 2. Particle diameti measurements vs. pH on selected purified dispersions were mai at 20°C using a Brookhaven instrument equipped with a BI 9000 AT digital autocorrelator and with a solid state las< (wavelength 532 nm, 125 mW) . The value from the cumula algorithm and second order fit (quadratic) was chose Diluted dispersions of microgel particles were prepared
0.01 M NaCl solution. The dispersion pH was adjusted by addi either HCl or NaOH.
1H NMR spectroscopy. Purified microgel latexes were dissolve in CDCI3 and their spectra were recorded. The integrate intensity of the signal at about 3.5 ppm due to oxyethyle protons from the - (CH2-CH20) n- groups was used in order t estimate the PEGMA stabilizer contents of the microgel late particles.
Table 3. Summary of the stabilizer and initiator types particle diameters and stabilizer contents of microgels.
Figure imgf000038_0001
Example 4: Formation of emulsions
All water used was de-ionised and doubly-distilled water from a Fistreem Cyclon purification water system. Three model oils,- n-dodecane, Ω-hexadecane and n-amyl acetate, were used to prepare the emulsions
Stock solutions of the dispersions at the desired solid content were prepared by diluting the concentrated dispersions in water. The solution pHs of known volumes (5 mL) of the dilute dispersion were adjusted as required by adding a few drops of concentrated HCl or NaOH solution. The pH of the dispersions was monitored with a pH meter. The dispersions were then homogenised together with 5 mL of the oil using an IKA Ultra-Turrax T-18 basic homogeniser with a 10 mm dispersing tool operating at 6,000 to 12,000 rpm for two minutes.
The conductivity of the emulsions immediately after preparation was measured using a digital Conductivity Meter Hanna, model Pri o 5. A measurable conductivity indicated formation of an oil-in-water emulsion, whilst no measurable conductivity indicated formation of a water-in-oil emulsion.
The emulsion type was determined by the 'drop, test'.
-This involved observing whether a drop of the emulsion dispersed quickly when added to either pure water or to the corresponding pure oil. Rapid dispersion indicated that the continuous phase of the emulsion was the same as the diluent (either water or oil) .
The emulsion droplets were also observed by optical microscopy. A small, dilute sample of the emulsion was put on a microscope slide and viewed with a microscope fitted with a camera. This technique was used to estimate the mean droplet particle size.
Example 5
DMA-MMA diblock (17.5 K) /PS latex emulsification
The emulsion formed from equal volumes of n-dodecane and 2 wt.% of the latex dispersion at pH 8 was a white oil- in-water emulsion which showed no signs of coalescence. Reducing the pH of the dispersion to pH 7 led to limited coalescence. Further lowering of the pH led to increased coalescence and at pH 1.9 practically no emulsion was observed. In all cases an oil-in-water (O/W) emulsion was formed initially at neutral pH (see Table 4) .
Table- 4. Emulsification tests for diblock copolymer- stabilised polystyrene latexes
Figure imgf000040_0001
Note 1: D = n-dodecane, AA = n-amyl acetate, H = n- hexadecane
Conditions: 5 mL latex (2 wt.%) + 5 mL oil @ 12,000 rpm and 20 °C.
#: Insufficient emulsion.
Using n-hexadecane and n-amyl acetate as the oil phases no emulsion formation was observed at pH 2 but at pH 7 stable emulsions were observed. The n-hexadecane emulsion was of the oil-in-water type whereas when the oil phase was n-amyl acetate a water-in-oil emulsion was observed. In all cases the pH-responsive character of the latex particles led to demulsification at low pH.
Example 5
DMA5Q-Sty macromonomer (8.2 K) /PS latex emulsification
The emulsion formed from equal volumes of n-hexadecane and 2 wt.% of the latex dispersion at pH 8.3 was a white oil-in-water emulsion. On reducing the pH of the dispersion to pH 2, no emulsion formation was observed (see Tables 4 and 5) . Again, the pH-responsive character of the latex particles was observed. More stable emulsions were formed if emulsification was carried out using a lower speed of the homogeniser (6,000 rpm).
Table 5. Emulsification tests for macromonomer-stabilised
Figure imgf000041_0001
Note 1. H = Ω-hexadecane, D = n-dodecane Conditions: 5 mL latex (2 wt.%) + 5 mL oil @ 6,000 rpm and 20°C.
Example 6 (Comparative Example) PEGMA (2 K) /PS latex emulsification
The emulsion formed from equal volumes of n-hexadecane and 1 wt.% of the latex dispersion at pHs ranging from 1.9 to 9.2 (see Table 6) was invariably a white oil-in- water emulsion. Using n-amyl acetate as the oil phase at both low pH (4.2) and high pH (9.5) led to the formation of a white water-in-oil emulsion. As expected, as the particles did not contain any responsive polymers, no pH- responsive character was observed and stable emulsions were formed at both low and high pH.
Table 6. Emulsification tests for PEGMA-stabilised polystyrene latexes
Figure imgf000042_0001
Note 1. H = n-hexadecane, AA = n-amyl acetate
Conditions: 5 mL (1 wt.%) latex + 5 mL oil @ 12,000 rpm and 20°C.
Example 7 DEA and DPA microgel latex emulsification
DEA microgel latex prepared using ACVA initiator (ACVA-
DEA) .
The emulsion formed from equal volumes of n-hexadecane and 1 wt.% of the latex dispersion at pH 8 was a white oil-in-water emulsion that showed no signs of coalescence. Reducing the pH of the aqueous' phase of the emulsion to pH 5 led to limited coalescence. Further lowering of the pH led to increased coalescence and at pH 2 practically no emulsion was observed.
Example 8
PEG2000MA/DEA microgel latex (PEGMA/DEA) The emulsion formed from equal volumes of n-hexadecane and 1 wt.% of the latex dispersion at pH 2 was very unstable (see Table 7). At pH 6.7 a stable oil-in-water emulsion with a small amount of oil separation was formed. However, at pH 10.0 a less stable emulsion is formed.
Table 7. Emulsification tests for microgel latexes
Figure imgf000043_0001
Figure imgf000044_0001
Note 1. H = n-hexadecane
Conditions: 5 mL latex (1 wt.%) + 5 mL oil @ 6,000 rpm and 20°C. a. Sodium dodecyl sulfate was used as a surfactant stabiliser during synthesis, but was removed after cleaning, hence only carboxylic groups derived from the
ACVA initiator are responsible for the colloidal stability.
# = Insufficient emulsion.
Example 9
PEG∑OQQMA/DPA microgel latex (PEGMA/DPA)
The emulsion formed from equal volumes of n-hexadecane and 1 wt.% of the latex dispersion at pH 2.0 was very stable and of the oil-in-water type. On increasing the pH to 5.5 an oil-in-water emulsion was still formed. At pH 10 an unstable water-in-oil emulsion was apparently formed, as judged by the drop test and. conductivity measurements .
Table 8 shows the droplet sizes for a number of different emulsions
Table 8. Droplet size range for selected emulsions.
Figure imgf000045_0001
Example 10
Surface tension vs. pH curves for selected latexes.
Surface tensiometry. Surface tension vs. pH curves were constructed using a Kruss K10 instrument. The solution pH was adjusted by adding either HCl or NaOH. The. surface tension of pure water (72 ± 1 mN m"1) was checked periodically during these measurements. Figure 3 shows the surface tension vs . pH behaviour of five selected polystyrene dispersions. Charge-stabilised polystyrene latex synthesised in the absence of any stabiliser (comparative example) shows no pH-responsive behaviour and its surface tension is similar to the pure water (72 mN/m) over the whole pH range studied. The surface tension of the PEGMA/PS latex (comparative example) is lower than pure water (around 60 mN/m) but is not pH-dependent . On the other hand, the three polystyrene latexes prepared with responsive polymers
(either the diblock DMAa0-MMA2o stabilisers or the DMA50-
Sty macromonomer) all show similar pH-responsive behaviour, i.e. high surface tension (low surface activity) at ' acidic pH and low surface tension (high surface activity) at alkaline pH. This suggests that the latter three latexes adsorb at the air/water interface at high pH. This pH-modulated surface activity was fully reversible and the adsorption/desorption of the latex particles at the air/water interface is believed to reflect their behaviour at the oil/water interface in the emulsions. These data generally indicate that the pH- responsive emulsifier behaviour of the polystyrene latexes is associated with the character of the steric stabiliser on the outside of the latex particles.
Example 11
Synthesis of sterically-stabilised polystyrene latex
Sterically-stabilised polystyrene latex particles were prepared by dispersion polymerisation using a poly[2-
(dimethylamino) ethylmethacrylate-block-methyl methacrylate] diblock copolymer as described in Example
1. Styrene (10.0 ml), azobisisobutyronitrile (AIBN) (100 mg) and the PDMA-PMMA diblock copolymer stabiliser (1.0 g, 10 wt.% based on styrene) were dissolved in 100 ml of a stirred, deoxygenated 70:30 v/v methanol/water mixture at 60 °C. Styrene polymerisation proceeded under nitrogen for 16 h at 60 °C. A stable milky-white polystyrene latex was obtained with a solids content of around 9.2 w/v%, indicating almost complete conversion of the styrene to polystyrene.
Serum replacement (ultrafiltration) as described in Example 2 was used to purify the latex particles. The weight-average particle diameter of the latex particles was determined to be 162 ± 20 nm by disc centrifuge photosedimentometry (Brookhaven BI-DCP instrument) . Scanning electron microscopy studies of the dried latex particles also indicated particle diameters in the range 150-180 nm. A 1H NMR spectrum (CDC13) of the dissolved polystyrene latex enabled the signals due to the DMA and
MMA residues of the stabiliser to be identified at δ 4.2 and δ 3.6, respectively. Comparison of these integrated peaks with those due to the polystyrene indicated a stabiliser content of around 8% by mass.
Example 12
Preparation of emulsions and effect of pH on emulsion stability
All water used was first passed through an Elga reverse osmosis unit and then a Milli-Q reagent water system, n- Dodecane was passed twice through chromatographic alumina to remove polar impurities. Aqueous solutions of analytical grade HCl and NaOH were used to adjust the pH of the latex dispersions.
A 2 wt.% stock solution of an aqueous dispersion of the latex according to Example 11 was prepared. The pH of known volumes (2 mL) of this dispersion was adjusted as required by adding a few drops of concentrated acid or base solution. The pH of the dispersions was monitored using a pH electrode. The dispersions were then homogenised together with 2 mL of n-dodecane using a Janke and Kunkel Ultra-Turrax homogeniser with a 10 mm head operating at 11 000 rpm for two minutes.
The emulsion type was determined by' observing whether a drop of the emulsion dispersed readily when added to either water or n-dodecane. All emulsions were equilibrated at 25°C in a thermostatted water bath.
The volume-weighted droplet size distributions of some of the emulsions formed were measured by light scattering using a Malvern Mastersizer 2000. The emulsion samples analysed were diluted in water at the pH of the original water phase. The distributions were characterised by the mean diameter and the median diameter (the diameter below which 50 % of the drops were sized) .
The emulsion drops were also observed by optical microscopy. A small, dilute sample of the emulsion was added to a haemocytometer cell (Weber Scientific) and viewed with a microscope fitted with a camera.
The emulsion formed from equal volumes of n-dodecane and 2 wt.% of the latex dispersion at its natural pH (ea. pH 8) was a white oil-in-water emulsion which showed no signs of coalescence. The median oil drop diameter was about 58 microns. Emulsions formed at low pH (2 to 3) were white oil-in-water emulsions which rapidly began to cream and coalesce after homogenisation of the liquids was halted, whilst at a pH between 7 and 5.5 the emulsions creamed. The pH of the aqueous phase which had separated from an emulsion originally formed at about pH 3 was adjusted to about pH 8 and the phases rehomogenised for one minute. A white oil-in-water emulsion which showed no evidence of coalescence over 24 hours was obtained, demonstrating that breaking of the emulsion by lowering the pH was reversible. After rehomogenisation, the volume weighted average diameter of the oil droplets was 61.0 microns and the median diameter was 56.0 microns. Thus the mean particle diameter was essentially unchanged compared to the original emulsion.
Example 13
The effect of varying the nature of the oil phase on the performance of the pH-responsive latex emulsifiers.
Five representative oils were chosen and their physical properties are summarized in Table 9.
Each of the oils listed in Table 9 was purchased from Aldrich and was used as received. The PDMA-PMMA diblock copolymer was prepared by group transfer polymerization according to the general protocol described by Baines et al Macromolecules, 1996, 29, 3416. Its block composition was confirmed to be approximately 80 mol % by 1H NMR spectroscopy. Gel permeation chromatography analysis indicated an Mn of 38,400 and a Mw/Mn of 1.14 vs. poly (methyl methacrylate) standards.
Latex Syntheses
The PDMA-PMMA diblock copolymer was used to prepare sterically-stabilized polystyrene latex via dispersion polymerization in a 7:3 methanol/water mixture using AIBN initiator as described previously. Purification was achieved using ultrafiltration with periodic replacement of the serum: surface tensiometry was used to confirm that the final latex was not contaminated with non- adsorbed block copolymer stabilizer. 1H NMR analysis of the resulting latex dissolved in CDC13 indicated a PDMA- PMMA stabilizer content of approximately 7 ± 1 wt. %. Scanning electron microscopy studies of the latex particles confirmed their spherical morphology and indicated a particle diameter range of 100-250 nm. This is consistent with both dynamic light scattering and disk centrifuge photosedimentometry studies.
1-Pyrenylmethyl methacrylate was prepared by the reaction of 1-pyrenemethanol (1.0 g) with excess methacryloyl chloride (0.494 g) in dry THF (25 g) for 5 h at 0 °C in the presence of triethylamine (0.87 g) and hydroquinone inhibitor (1 mg) . The resulting reaction was filtered to remove the amine salt and 10 wt. % Na2C03 aqueous solution was added to neutralize the excess methacryloyl chloride. The 1-pyrenylmethyl methacrylate was extracted with dichloromethane and dried with anhydrous Na2S04. This solution was filtered and the dichloromethane was removed under vacuum. 1H NMR spectroscopy confirmed the compound to be 1-pyrenylmethyl methacrylate and the yield (based on 1-pyrenemethanol) was calculated to be almost 100 %. Pyrene-labelled PS latex was synthesized under the same conditions as the PS latex described above using 1- pyrenylmethyl methacrylate as a comonomer (1.0 wt. % based on styrene) . The PDMA-PMMA stabilizer content of the pyrene-labelled PS latex was 6 ± 1 wt . % as judged by ■""H NMR studies of the dissolved latex in CDC13. Scanning electron microscopy was used to investigate the morphology and size distribution' of the pyrene-labelled PS latex. Emulsion Synthesis
Stock . solutions of the latexes at the desired solids content were prepared by dilution. The solution pH of 5 L .aliquots of the diluted .latexes was adjusted as required by adding a few drops of concentrated HCl or NaOH solution, using a pH meter to monitor the solution pH. The latex dispersions were then homogenized at 20°C with 5 mL of each of the five oils for two minutes using an IKA Ultra-Turrax T-18 homogenizer with a 10 mm dispersing tool operating at 12,000 rpm.
Emulsion stabilities after standing for 24 h at room temperature (20-25°C) were assessed by visual observation. In some cases a more accurate emulsion stability assessment was obtained using graduated vessels by monitoring the movement of the oil-emulsion and emulsion- water interfaces with time.
The four PS latexes used in this Example are summarized in Table 10. The first entry, SDS-PS, is simply a surfactant-stabilized PS latex, whereas the other three examples are sterically-stabilized latexes. A PDMA-PMMA diblock copolymer was used to prepare the DM7-PS latex and also the pyrene-labelled DM6-py-PS latex used for the confocal laser microscopy experiments (here the number within the sample code indicates the PDMA-PMMA stabilizer content of each latex by mass) . The DM2-PS latex was obtained simply by adjusting the purification protocol used to obtain the.DM7-PS latex: redispersion in methanol
(rather than water) led to desorption of most of the
- physically-adsorbed PDMA-PMMA chains from the latex surface and hence a much lower stabilizer content of 2 wt . % . The physicochemical properties of the five oils examined in this work are summarized in Table 9. These oils were selected because they were inexpensive, relatively involatile, had reasonably similar densities and, most importantly, allowed systematic variation of the oil polarity.
Various oil-in-water and water-in-oil emulsions were prepared using a pH-responsive sterically-stabilised polystyrene latex (DM7-PS) . A polydisperse n-dodecane- in-water emulsion was obtained at pH 8.2; these n- dodecane droplets are mainly spherical and disappear on adjusting the solution pH to below pH 3 due to coalescence, since the protonated particulate emulsifier no longer has any affinity for the oil phase. A water- in-1-undecanol emulsion is rather unstable and the droplets are non-spherical, suggesting that partial coalescence has already occurred prior to visual inspection. Isopropyl myristate-in-water emulsions appear to be relatively insensitive to variation of the solution pH. However, Mastersizer data (see Table 11) suggests that mean droplet diameters of around 60 μm are obtained at pH 2.6, compared to approximately 40 μm droplets at pH 8.4. Emulsions were also obtained using methyl myristate as the oil phase. The conductivity data
(see Table 11) confirm that a methyl myristate-in-water emulsion is obtained at pH 2.6, but an inverted water-in- ethyl myristate emulsion is obtained at pH 8.3. This phase inversion is shown schematically in Figure 2 .and proceeds without any macroscopic demulsification. Cursory inspection suggests that -bigger droplets - are obtained at pH 8.2 than at pH 2.6: the Mastersizer data confirms this effect since the mean droplet diameter at low pH is 50 μm, whereas at high pH it is approximately 140 μm (see Table 11) . Similar pH-induced catastrophic phase inversion behavior was observed, again without concomitant demulsification, using cineole instead of methyl myristate. Thus the type of emulsion that is formed and its behavior in response to changes in the solution pH appears to depend critically on the polarity of the oil phase.
The PDMA-PMMA stabilizer content of the original sterically-stabilized PS latex (DM7-PS) used in this work was 7 wt. % as judged by 1H NMR spectroscopy. However, it was discovered that if this latex was redispersed in methanol (rather than water) during purification most of the stabilizer was removed from the latex surface. This is because most of the stabilizer is merely physically adsorbed rather than chemically grafted; since methanol is a good solvent for both blocks (PDMA and PMMA) significant copolymer desorption occurs. The final stabilizer content of the methanol-treated latex was only 2 wt. %. This lower stabilizer content has a profound effect on the latex's performance as a particulate emulsifier, see Table- 12. Water-in-n-dodecane emulsions are formed at pH 9.2, with demulsification occurring at low pH. With cineole, there is no change in emulsion type, but emulsions prepared using the PS latex that contained 2 wt. % stabilizer were much less stable, had bigger mean droplet diameters and had higher polydispersities than those prepared using the original PS latex (7 wt. % stabilizer content) . Thus it is clear that the surface concentration of the stabilizer chains is important in determining the wettability of the latex particles.
Table 13 summarizes the results obtained by systematically reducing the latex concentration from 2.00 % to 0.125 % for two oils. For n-dodecane-in-water emulsions prepared at around pH 8.2, there is a clear trend of increasing droplet size and polydispersity at lower latex concentrations, with a concomitant reduction in long-term emulsion stability. For water-in-methyl myristate emulsions at approximately the same pH, very poor emulsions were obtained at or below latex concentrations of 0.25 %. A similar, though less certain, trend was observed for methyl myristate-in-water emulsions formed at low pH.
In view of the catastrophic phase inversion observed for the methyl myristate-in-water emulsions on varying the solution pH, this system was studied in more detail. All previous emulsion formulations had involved equal volumes of the oil and aqueous phases, but in this series of experiments the oil volume fraction was systematically varied from 20 to 80 % .(see Table 14) . It was found that catastrophic phase inversion only occurred at a volume fraction of 50 % methyl myristate. Lower volume fractions gave only methyl myristate-in-water emulsions at both pH 2-3 and pH 8-9. Similarly, higher volume fractions produced solely water-in-methyl myristate emulsions, regardless of the solution pH. Moreover, the best long- term emulsion stabilities were also obtained at 50 % methyl myristate.
The latex particles are spherical, with a mean latex diameter of around 130 nm and a relatively narrow particle size distribution. The pyrene content of this latex was estimated to be approximately 1 %, as judged by 1H NMR spectroscopy.
The results indicate that the polarity of the oil phase has a profound effect on. the emulsifier performance of sterically-stabilized polystyrene latex. Low polarity oils such as n-dodecane lead to pH-responsive oil-in- water emulsions, whereas relatively polar oils such as 1- undecanol lead to pH-responsive water-in-oil emulsions. In both cases lowering the solution pH leads to rapid demulsification. However, using oils of intermediate polarity (such as methyl myristate or cineole) can lead to catastrophic phase inversion as the solution pH is lowered: oil-in-water emulsions formed at pH 8 can become water-in-oil emulsions at pH 2-3, with no demulsification being observed. However, this inversion only occurs within a narrow volume fraction range (around 0.50 with respect to the oil phase) . Moreover, the surface concentration of the steric stabilizer is also important in determining the nature of the emulsion, as well as its pH-responsive behavior.
Table 9. Summary of the physicochemical properties of the five oils evaluated in Example 13.
Figure imgf000055_0001
Polarities calculated from experimental values of the oil-air and oil-water surface tensions.
Table 10. Stabilizer type, stabilizer content and particle size of the four polystyrene latexes used as particulate emulsifiers in this study.
Figure imgf000055_0002
Figure imgf000056_0001
a) As judged by 1H NMR spectroscopy. b) As determined using dynamic light scattering at pH 6 except for DM2-PS, which was determined at pH 2.2.
Table 11. Characterization data obtained for the emulsions prepared by adding 2 wt. % aqueous polystyrene latex (PDMA-PMMA stabilizer content = 7 wt . %; DM7-PS) to each of the five oils in turn. Equal volumes of oil and latex dispersion (at either pH 2-3 or 8-9) were used and homogenisation was carried out at 12,000 rpm for 2 min. at 20 °C.
Figure imgf000056_0002
1. As determined by visual inspection.
2. As estimated using optical microscopy.
3. As measured using a Malvern Mastersizer instrument.
Table 12. Comparison of the pH-responsive behavior of 50 % emulsions prepared using a non-polar oil (n- dodecane) and a polar oil (cineole) with a 1.0 wt. % sterically-stabilized polystyrene latex containing either 2 wt. % or 7 wt. % PDMA-PMMA stabilizer, respectively.
Figure imgf000057_0001
1. As determined by visual inspection. 2. As estimated using optical microscopy.
3. As measured using a Malvern Mastersizer instrument.
Table 13. Effect of varying the latex concentration on the properties of 50 % emulsions - prepared with either a non-polar oil (n-dodecane) or a polar oil (methyl myristate) using the PDMA-PMMA-stabilized polystyrene latex containing 7 wt . % stabilizer (DM7-PS) .
Figure imgf000057_0002
1. As determined by visual inspection.
2. As estimated using optical microscopy.
3. As measured using a Malvern Mastersizer instrument.
Table 14. Effect of varying the methyl myristate/water volume composition on the properties of the emulsions obtained using 2 wt. % of a PDMA-PMMA stabilized polystyrene latex (DM7-PS) .
Figure imgf000058_0001
1. As determined by visual inspection. 2. As measured using a Malvern Mastersizer instrument.
Example 14
Seeded emulsion copolymerization of core/shell latex particles and their uses as pH-responsive particulate emulsifiers.
In this Example seeded emulsion copolymerization was used to produce PS/P (DMA-stat-EGDMA) core/shell latex particles for use as pH-responsive . particulate emulsifiers for oil-in-water emulsions. Emulsion polymerization offers a number of advantages (i) unlike dispersion polymerizations, emulsion polymerizations are conducted in purely aqueous media, which is environmentally benign; (ii) free radical polymerization chemistry is facile compared to GTP chemistry (which was required to produce the diblock polymer stabilizer) ; (iii) in principle, a high surface concentration of pH- responsive polymer can be achieved; (iv) a cross-linked pH-responsive shell may be more robust than a merely physically adsorbed diblock copolymer stabilizer.
Styrene (S) , DMA and EGDMA (Aldrich) were treated with basic alumina in order to remove inhibitor, and stored at
-20 °C before use. Polyoxyethylene sorbitan monooleate
(Tween 80) , ethanol and n-dodecane were used as received.
■ 2, 2' -Azobis (2-amidinopropane) hydrochloride (AIBA) was used after recrystalization. Doubly-distilled de-ionized water was used in all the polymerizations.
Synthesis of PS/P (D A-stat-EGDMA) particles. Seeded emulsion copolymerizations of DMA and EGDMA were performed in the presence of PS seed particles in batch mode at 60 °C (Table 15) . The synthetic procedure was as follows: PS latex (0.893 g; solid content 9.6 wt . %) was added to a solution of Tween 80 (40 mg) , DMA and EGDMA in doubly-distilled water (total water volume, 43 L) at room temperature, and the system was stirred at 250 rpm for 18 h for PS seed particles to be swollen with DMA and EGDMA. The polymerization was started at 60 °C by injecting an aqueous solution of AIBA solution (0.18 g AIBA in 7 ml water) to this stirred system and allowed to proceed for 24 h.
Table i5. Recipes for production of PS/P (DMA-stat-EGDMA). composite latex particles by seeded emulsion copolymerization. Total -shell content of composite particles
Ingredients
1D t% 2ΩvΛ%
PS emulsion5-' 0) 9.34 9.34
Tween 80 (9) 0.04 0.04
DMA (g> 0.095 0.212
EGDMA* (mg) 5 11
AIBA (g> 0.1798 0.1798
Water (g) 44.7 44.7
* 60"C, s h, j, 100 rpm (a magnetic stir bar)
* Solid content, 9.56 wt.%; PS seed particles, 0.833 g « EGDMA content Is 5wt.% bases on .omonom«r
Characterization of PS/P(DMA-stat-EGDMA) particles.
Scanning electron microscopy (SEM) studies were made using a Leo Stereoscan 420 instrument. FTIR spectroscopy studies were carried out on samples dispersed in KBr disks using a Nicolet Magna-IR Series II spectrometer. Hydrodynamic particle diameters were measured by dynamic light scattering using a Malvern 4700 instrument.
Emulsion preparation. Emulsions of different volumes of n-dodecane and aqueous latex dispersion containing 1 wt. % of particles were prepared using an Ultra TURRAXR IKA T18 basic (IKAR Works, Inc.) operating at 12,000 rpm for 2 min at 25 °C at either pH 3 or pH 9. The emulsion type was determined via conductivity measurements and using the drop test.
Characterization of the emulsions. The emulsion droplets were observed by optical microscopy (James Swift MP3502, Prior Scientific Instruments Ltd.). A Malvern Mastersizer S instrument was used to determine the mean particle diameter of the droplets. The latex superstructures surrounding the emulsion droplets were observed by SEM after critical point drying (CPD) . CPD was performed with a Polaron E3000 critical point dryer using ethanol. as an intermediate fluid and carbon dioxide as a transitional fluid. Latex characterization. For the PS seed latex particles, core-shell PS/P (DMA-stat-EGDMA) latex particles with shell loadings of 10 and 20 wt. %, fairly uniform submicron-sized particles were obtained, with a mean particle diameter of around 150-160 nm. However, the polydispersities were such that it was not possible to confirm that the two core-shell latexes were actually larger than the original PS seed latex. The EGDMA cross- linker content of the shell was 5 wt. %; its addition was essential to prevent the formation of water-soluble PDMA. In initial attempts at seeded emulsion syntheses, coagulation always occurred prior to copolymerization whenever the PS seed latex, DMA, EGDMA and water were mixed together, regardless of the order of addition. This colloidal instability was due to the solution pH being close to the isoelectric point of the PS seed latex, which was around pH 8. In order to prevent this coagulation, more Tween 80 was added to the seeded emulsion copolymerization formulation. This refinement allowed the synthesis of stable composite particles with hydrodynamic diameters (Dz) of 164 nm (polydispersity = 0.055) and 213 nm (0.14) being obtained at pH 6 for the 10 wt. % and 20 wt. % shell contents, respectively. The Dz values for the composite particles were both larger than that of the original PS seed particles (155 nm) and the higher shell mass loading led to larger particles, as expected. Thus these DLS results indicated that the PS seed particles were coated with a cross-linked, hydrated P (DMA-stat-EGDMA) shell. Moreover, the Dz values for the 10 wt. % shell latex at . pH 3 and 9 were determined to be 305 and 230 nm, respectively. Thus the P (DMA-sta -EGDMA) shell was highly swollen and expanded at pH 3 due to the high degree of protonation of the cross-linked DMA residues (the pKa of DMA homopolymer is around pH 7.0- 7.5). However, deprotonation occurred at pH 8 and collapse of the shell layer occurs.
FT-IR studies confirmed that composite particles were produced since an ester carbonyl band at 1736 cm-1 assigned to the DMA residues was absent in the PS seed latex but present in the purified 10 and 20 wt. % ^ore- shell' -particles. Moreover, the relative band intensity was -higher for the 20 % shell latex than the 10 % shell latex, as expected.
Characterization of emulsions. Using PS/P (DMA-stat- EGDMA) latex particles as a particulate emulsifier, n- dodecane-in-water emulsions were obtained after homogenization of 50/50 and 60/40 mixtures of latex and n-dodecane. For example, a polydisperse n-dodecane-in- water emulsion was obtained at pH 8.4 using 20 wt. % shell composite particles after homogenization of a 50/50 mixture of latex and n-dodecane. The n-dodecane droplets are mainly spherical and the mean droplet diameter of 63 μm obtained from Mastersizer data was in good agreement with the optical microscopy images. On the other hand, no emulsions were obtained at pH 3 because the protonated, cationic PDMA shell is too hydrophilic to wet the surface of the oil droplets. These results indicate that PS/P (DMA-stat-EGDMA) latex particles can act as an effective pH-responsive particulate emulsifier. When homogenization of a 40/60 mixture of the latex and n- dodecane or a 50/50 mixture of PS seed latex and n- ■ dodecane was conducted, inverted water-in-n-dodecane emulsions were obtained at pH 9.
In Example 14 PS/P (DMA-stat-EGDMA) core-shell latex particles were successfully prepared from a PS seed latex. These PS . and PS/P (DMA-stat-EGDMA) latexes were characterized in terms of their particle size, morphology and composition using dynamic light scattering, SEM and FT-IR spectroscopy, respectively. Using the PS/P (DMA- stat-EGDMA) latex particles as pH-sensitive particulate emulsifiers, polydisperse n-dodecane-in-water emulsions were prepared at pH 9. The emulsion type and mean droplet diameter were determined by conductivity measurements and optical microscopy. Critical point drying allowed the preservation of the latex superstructures surrounding the emulsion droplets, which could be observed by SEM. These emulsions were readily demulsified at pH 3, due to desorption of the latex particles from the oil/water interface. The advantage of these pH-responsive latexes is that their synthesis only involves emulsion polymerization, whereas the sterically-stabilised latexes require group transfer polymerization for the production of the steric stabilizer.
Example 15
This Example describes the production of Shell Cross- Linked (SCL) Micelles and their use as Stimulus- Responsive Particulate Emulsifiers
1. Synthesis of PE045-GMA18-DEA3o triblock copolymer by ATRP
The PE045-GMAi8-DEA3o triblock copolymer was synthesised using similar conditions to those described in S. Liu, J. V. M. Weaver, M. Save, S. P. Armes, Langmuir, 2002, 18, 8350. A block composition of PE05-GMA3o-DEA50 was targeted, but 1H NMR studies of the purified copolymer indicated a final block composition of PEO45-GMAι8-DEA30 suggesting either less than ideal blocking efficiencies or else some fractionation occurred during the purification step. The PE05-Br macro-initiator (4.000 g, 1.9 mmol) and GMA monomer (9.143 g, 57.1 mmol) were added to a reaction flask and were degassed under nitrogen purge for around 30 min. Methanol was degassed separately and 13 mL of this solvent was added to the monomer/initiator mixture via double-tipped needle, followed by a freeze-pump-thaw cycle. Cu(I)Cl (189 mg, 1.9 mmol) catalyst and 2, 2' -bipyridine (594 mg, 3.81- mmol) ligand were introduced into the reaction flask at room temperature to start the polymerisation. After the conversion of GMA had reached more than 95 % as judged by XH NMR,1 degassed DEA monomer (17.620 g, 95.2 mmol) diluted with degassed methanol (18 mL) was transferred to the reaction flask via double-tipped needle. After a further 12-15 h, the dark brown reaction solution was exposed to air and diluted with methanol; termination occurred rapidly, as indicated by the colour change from brown to green/blue due to the aerial oxidation of Cu(I) to Cu(II) . The copper catalyst was separated from the triblock copolymer solution by passing the methanolic solution through a silica gel column. After removal of the methanol via vacuum distillation, the copolymer was dried in a vacuum oven at room temperature to yield a white,' semi-crystalline solid. GPC analysis of the triblock copolymer using DMF eluent showed a symmetrical, unimodal GPC trace with no evidence for any residual PE05~Br macro-initiator [GPC set-up comprised three Polymer Laboratories PL gel 5 μm Mixed ΛB' columns and a refractive index detector; the DMF eluent (containing 10 mM LiBr) was pumped . at a flow rate of 1.0' mL min"1 and the column temperature was set at 70 °C] .
Calibration was achieved using a series of near- monodisperse poly (methyl methacrylate) standards and indicated an Mn of 18,300 and an Mw/Mn of 1.25 for this PE05-GMAi8-DEA3o triblock copolymer.
1.1 Preparation of the PEO45-GMAi8-DEA30 triblock copolymer micelles and shell cross-linked micelles
The PE045-GMAi8-DEA3o triblock copolymer was molecularly dissolved as a 2.0 wt. % solution at pH 2. The solution pH was slowly adjusted to pH 12 using dilute NaOH solution to form well-defined DEA-core micelles. Micellisation was confirmed using DLS, which gave an intensity-average micelle diameter of 26 nm. Shell cross-linking was achieved by adding specific quantities of divinyl sulfone (DVS) to the micellar solution at pH 12 and stirring at room temperature for around 5-6 h at 20 °C. The target degree of cross-linking was 50 % as given by y = 2 [DVS] /[GMA] x 100 %. The pH of the SCL micellar solutions was adjusted from pH 12 to approximately pH 9 after DVS cross-linking. Successful shell cross-linking was confirmed by both DLS studies and also using a Polymer Laboratories Particle Size
.Distribution Analyser; these sizing techniques indicated
SCL micelle diameters of 31 nm and 28 nm respectively at pH 3. Since the noncross-linked micelles and SCL micelles have comparable dimensions, this proved that no significant micellar fusion occurred during shell cross- linking.
1.2 Preparation of the SCL micelle-stabilised emulsions
• 5 mL aqueous solutions of the SCL micelles were taken from the 2 wt. % stock solution and the pH was adjusted as required using concentrated HCl or NaOH. The SCL micelle solutions were then homogenised at 20 °C using 5 mL of . 1-undecanol for two minutes using an IKA Ultra- Turrax T-18 homogenizer with a 10 mm dispersing tool operating at 12,000 rpm.
Emulsion stabilities were assessed using optical microscopy after standing for' at least 24 h at 20 °C. The emulsion type was determined by both conductivity measurements and also by dropping small quantities of the emulsion into both oil and water and observing either homogenisation (continuous phase is the same as the diluent) or droplet stability (dispersed phase is the same as the diluent) .
1.3 Characterisation of the PE045-GMA3o-DEA50 triblock copolymer, noncross-linked micelles and SCL micelles
All 1H NMR spectra were recorded on 1.0 w/v % copolymer solutions in D20 using a Bruker Avance DPX 300 MHz spectrometer. Dynamic light scattering (DLS) studies were performed on a Brookhaven Instruments Corp. BI-200SM goniometer equipped with a BI-9000AT digital correlator using a solid-state laser (125 mW, λ = 532 nm) at a fixed scattering angle of 90°. The intensity-average hydrodynamic diameter, <Aι> , and polydispersity ( 2/-T 2) were calculated for each micellar solution before and after cross-linking by cumulants analysis of the experimental correlation function (M. Save, J. V. M. Weaver, S. P. Armes, P. McKenna, Macromolecules, 2002, 35, 1152 and Chu, B. Laser Light Scattering; Academic Press: New York, 1974) .
The PEO45-GMAi8-DEA30 triblock copolymer dissolved molecularly in aqueous solution at low pH; on addition of
NaOH, micellisation occurred above pH 7-8, as judged by DLS' and 1H NMR. DLS studies indicated dimensions of around 2 nm below pH 7 (molecularly dissolved copolymer chains) and micelle diameters above pH 7 of around 26 n (aggregated copolymer chains) . 1H NMR spectra of the micelles' and SCL micelles as a function of pH are shown in Figure 4. These micelles comprised • DEA cores, GMA inner shells and PEO outer coronas.
1.4 Characterisation of the SCL micelle-stabilised emulsion
Conductivity Measurements . The conductivity of the emulsions immediately after preparation was measured using a digital conductivity meter (Hanna model Primo 5) . A high conductivity indicated an oil-in-water emulsion and a low (immeasurable) conductivity (< 1 μS cm-1) indicated a water-in-oil emulsion.
Optical Microscopy (OM) . A drop of the diluted emulsion was placed on a microscope slide and viewed using an optical microscope fitted with a digital camera (James Swift MP3502, Prior Scientific Instruments Ltd.). This technique was used to estimate the mean droplet particle diameter.
After emulsification, the emulsions were allowed to stand for 24 h. After this time, the emulsion type was determined by both drop test and conductivity measurements and emulsion size was determined by optical microscopy. The results are shown in Table 16.
Emulsion type determined via conductivity measurement and drop test.
Figure imgf000068_0001
Table 16. Summary of experimental data for a 50:50 1- undecanol-in-water emulsion prepared using 2 % SCL •micelles obtained from a PE045-GMAi8-DEA3o (target degree of cross-linking using DVS = 50 %) .
Optical microscopy studies confirm the presence of polydisperse SCL micelle-stabilised emulsions of around 20-80 μm diameter at pH 9.2: under these conditions the DEA cores are deprotonated and hence hydrophobic and are therefore capable of adsorbing onto the oil droplets. However, at pH 2.0, the emulsion size is dramatically reduced to around 10-20 μm. Moreover, the emulsion stability is dramatically reduced so that only 2 % of the emulsion phase remains. Thus almost complete demulsification of the 1-undecanol droplets occurs at low pH. Under these conditions the SCL micelles are significantly more hydrophilic since the DEA cores are protonated and no longer have any affinity for the oil phase. This leads to detachment of the SCL micelles from the oil droplets, producing rapid coalescence. The same observations were made regardless of whether the two emulsions at pH 9.2 and pH 2.0 were prepared separately or whether acid was added to the pH 9.2 emulsion to obtain pH 2.0. Thus although acid-induced demulsification is- not quite as complete as that demonstrated for sterically-stabilised latexes, Example 15 clearly shows that the SCL micelles act as a pH-responsive particulate emulsifier.
The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.
All of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.
Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) , may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
The invention is not restricted to the details of any foregoing embodiments . The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

Claims
1. Use of a particulate emulsifier comprising at least one polymer, in an oil-in water or water-in- oil emulsion, wherein the hydrophilic/hydrophobic balance of the polymer can be varied on application of a stimulus to break the emulsion, or to cause phase inversion.
2. Use of claim 1, wherein the breaking of the emulsion, or the phase inversion, is reversible.
3. Use of claim 1 or 2, wherein the particulate emulsifier comprises at least one ' responsive polymer, and wherein the stability of the emulsion is dependent upon the response of the responsive polymer to at least one environmental condition.
4. Use according to any one of the preceding claims, wherein the particulate emulsifier is a polymeric microgel, or has a core/shell latex structure.
5. Use of claim 3 or 4, wherein the responsive polymer responds to a variation of an external condition by a change in the contact angle of the surface of the particles of the . particulate emulsifier with an oil-water interface, measured into the water phase.
6. Use of any one of the claims 3 to 5, wherein the
■ responsive polymer responds to a variation of an external condition by a steric or conformational change, by a change in protonation, by a change in salvation, or by a change in hydration.
7. Use according to any one of the preceding claims, wherein application of a stimulus causes breaking of the emulsion.
8. Use according to any one of claims 1 to 6, wherein application of a stimulus causes phase inversion.
9. Use according to claim 5, wherein the change in contact angle is at least 10°
10. Use according to any one of the preceding claims, wherein the particles of the particulate emulsifier are formed essentially entirely from one or more responsive polymer (s).
11. Use according to claim 10, wherein one responsive polymer forms the particle core whilst another forms the particle shell.
12. Use according to any one of claims 3 to 9, wherein the responsive polymer (s) form a shell on an inert particle core, or wherein the responsive polymer (s) form a particle core are surrounded by a non-responsive shell.
13. Use according to any one of the preceding claims, wherein the particles of the particulate emulsifier are in the size range 1 x 10~9 to 1 x 10"5m.
14. Use according to any one of the preceding claims, wherein the stimulus comprises a change in temperature, a change in pH, a change in ionic strength, or any combination thereof.
15. Use according to claim 2, wherein the breaking, or phase inversion, of the emulsion is reversible by reversing an environmental change.
16. Use according to any one of the preceding claims, wherein the polymer has affinity for oil and water at pH values on one side of its pKa value.
17. Use according to any one of the preceding claims, wherein the polymer (s) exhibits inverse temperature solubility behaviour in aqueous solution
18. Use according to any one of the preceding claims, wherein the polymer exhibits variable hydrophilicity depending on pH and comprises at least one acidic or basic functional group on the polymer chain.
19. Use according to claim 18, wherein the polymer is responsive within the range of from pH 2 to pH 12.
20. Use according to claim 18 or 19, wherein the polymer is polyDMA, polyMEMA, polyDEA, polyDPA, poly2-VP, poly4-VP, polyTBA, polyAA, or polyMAA.
21. Use according to any one of the preceding claims, wherein the water solubility of the polymer can be changed by changing the ionic strength of an aqueous solution of the polymer.
22. Use according to claim 21, wherein the polymer is poly (ethylene oxide), polyDMA, or polyMEMA.
23-. Use according to claim 4, wherein the microgel comprises cross-linked polymer particles wherein at least some of the polymer chains forming the particles comprise a responsive polymer.
24. Use according to claim 23, wherein the polymer particles are stabilised in suspension by electrical double layer (charge or surfactant) stabilisation, or by steric (polymeric) stabilisation.
25. : Use according to claim 23 or 24, wherein the microgel is a charged stabilised microgel formed from cross-linked polyDEA.
26. Use according to claim 23 or 24, wherein the microgel comprises a cross-linked responsive polymer core that is sterically stabilised.
27. Use according to claim 26, wherein the steric stabilisation is provided by polymer chains that are different from those forming the microgel core.
28. Use according to claim 26 or 27, wherein a steric stabilising layer also comprises a responsive polymer, or wherein a steric stabilising layer comprises a non-resporisive polymer.
29. Use according to claim 28, wherein the responsive polymer comprises . a poly (meth) acrylate' or poly (meth) acrylamide .
30. Use according to claim 28, wherein the non- responsive polymer comprises poly(N- vinypyrrolidone) .
31. Use according to any one of claims 23 to 30, wherein the microgel comprises a charge-stabilised polyDEA microgel, a microgel comprising a polyDEA microgel core stabilised by a polyDMA steric stabilising layer, a microgel comprising a polyDEA core stabilised by a chemically grafted PEG20ooMA layer, or a microgel comprising a polyDPA core stabilised by a chemically grafted PEG2oooMA layer.
32. Use according to claim 4, wherein the particulate emulsifier has a core/shell latex structure and comprises a sterically-stabilised polymer latex wherein the steric stabiliser comprises a responsive polymer.
33. Use according to claim 32, wherein the particulate emulsifier is substantially insoluble in either phase of the emulsion.
34. Use according to claim 32, or 33, wherein the latex is formed by emulsion polymerisation or by dispersion polymerisation.
35. Use according to any one of claims 32 to 34, wherein the latex core is formed from a polymer of styrene or a derivative thereof, an acrylate or methacrylate, a diene, chloroprene, vinyl chloride, vinyl acetate, acrylonitrile, acrylamide or ethylene.
36. Use according to any one of claims 32 to 35, wherein the steric stabiliser of the polymer latex comprises an amphiphilic block copolymer.
37. Use according to claim 36, wherein the block copolymer comprises one block which does not have affinity for the continuous phase of the emulsion and absorbs onto the latex particle surface to form an anchor and another block which extends into the dispersion medium to . form a steric barrier against flocculation or coagulation and which comprises a responsive polymer.
38. Use according to claim 37, wherein the anchor block comprises a hydrophobic alkyl methacrylate and the stabilising block comprises a tertiary amine substituted methacrylate.
39. Use according to any one of claims 32 to 35, wherein the polymer latex steric stabiliser comprises a statistical and/or graft copolymer.
40. Use according to claim 4, wherein the particulate emulsifier has a core/shell latex structure and comprises • a sterically-stabilised polymer latex wherein stabilisation is provided by chemically grafting a macromonomer onto the outer surface of the latex particles.
41. Use according to claim 40, wherein the macromonomer comprises a responsive polymer and a polymerisable end group that can be chemically incorporated into the polymer latex as the latex particles are synthesised.
42. Use according to claim 41, wherein the macromonomer comprises a poly (meth) acrylate wherein the polymerisable group is a styrene residue.
4-3. Use according to any one of claims 1 to 3, wherein the particulate emulsifier has a • core/shell structure comprising an inorganic core with a responsive polymer on the outer surface forming a sterically-stabilising shell.
44. Use according to claim 43, wherein the core comprises a silica , alumina, Fe203, BaS04, CaS04 or CaC03 particle.
45. Use according to claim 43 or 44, wherein the responsive polymer shell comprises poly (meth) acrylate or poly (meth) acrylamide .
46. Use according to any one of claims 1 to 3, wherein the particulate emulsifier has a core/shell structure comprising a responsive polymer shell polymerised around a polymeric particle core.
47. Use according to claim 46, wherein the core comprises a polymer of styrene or a derivative thereof, an alkylmethacrylate, an alkyl acrylate, vinyl chloride, ethylene, or vinyl acetate.
48. Use according to claim 46 or 47., wherein the responsive shell comprises a poly (meth) acrylate or poly (meth) acrylamide .
49. Use according to any one of claims 1 to 3, wherein the ■ particulate emulsifier has a core/shell structure comprising shell cross-linked micelles.
50. Use according to claim 49, wherein the micelles comprise a responsive polymer core and/or shell.
51. Use according to claim 49 or 50, wherein the micelles comprise a block copolymer.
52. Use according to claim 51, wherein the block copolymer comprises polyDMA, polyDEA, polyDPA, polyMEMA or poly (propylene oxide)..
53. Use of any one of the preceding claims, wherein the emulsion is an oil-in-water emulsion.
54. Use according to any one of the preceding claims, wherein the droplet size of the emulsion is in the range of from 0.3 to lOOμm.
55. Use according to any one of the preceding claims, wherein the emulsion comprises an additional component selected from food additives, flavourings, agrochemicals, pharmacologically active compounds, cosmetic ingredients, or fragrances.
56. Use according to any one of the preceding claims, substantially as described in Examples 1 to 12.
57. Use according to any one of the preceding claims substantially as described in Examples 13 and 14.
58. Use according to any one of the preceding claims substantially as hereinbefore described.
59. Use of a particulate emulsifier comprising at least one responsive polymer in the production of an emulsion, wherein the stability of the emulsion is dependent on at least one .environmental^ condition.
60. Use of claim 59, wherein the particulate emulsifier has any one of the features of claims 1, 3 to 6, 9 to 14, and 16 to 52.
61. Use of claim 59 or 60, wherein the emulsion is as claimed in any one of claims 53 to 55.
62. Use of a particulate emulsifier comprising a sterically-stabilised polymer latex for stabilising an oil-in-water emulsion.
63. An oil-in-water or water-in-oil emulsion ■ ■ comprising at least one particulate emulsifier comprising a polymer wherein the
- hydrophilic/hydrophobic balance of the polymer can be varied on application of a stimulus to break the emulsion, or to cause phase inversion.
64. An emulsion according to claim 63, wherein the particulate emulsifier has any one of the features of claims 1, 3 to 6, 9 to 14, and 16 to 52.
65. An emulsion according to claim 63 to 64, as claimed in any one of claims 53 to 55.
66. An emulsion according to any one of claims 63 to 65, substantially as described in Examples 1 to 12.
67. An emulsion according to any one of claims 63 to 65, substantially as described in Examples 13' and 14.
68. An oil-in-water or water-in-oil emulsion comprising at least one particulate emulsifier substantially as hereinbefore described.
69. An oil-in-water or water-in-oil emulsion comprising at least one particulate emulsifier comprising a polymer, wherein the stability of the emulsion is dependent on at least one environmental condition.
70. An emulsion .according to claim 69, wherein the particulate emulsifier has any one of the features of claims 1, 3 to 6, 9 to 14, and 16 to 52.
71. An emulsion according to claim 69 or 70, as claimed in any one of claims 53 to 55.
72. An emulsion according to any one of claims 69 to 71, substantially as described in Examples 1 to 12.
73. An emulsion according to any one of claims 69 to 71, substantially as described in Examples 13 and 14.
74. An emulsion according to any one of claims 63 to 74, for use in foods, agrochemicals, cosmetics, personal/home care product formulations, or pharmaceutical formulations.
75. A method for stabilising an oil-in-water or water- in-oil emulsion . wherein there is used a particulate emulsifier comprising a polymer wherein the hydrophilic/hydrophobic balance of the polymer can be varied by application of a stimulus.
76. A method according ,to claim 75, wherein the particulate emulsifier has any one of the features of claims 1, 3 to 6, 9 to 14, and 16 to 52.
77. A method according to claim 75 or 76, wherein the. emulsion is as claimed in any one of claims 53 to 55.
78. A method for the preparation of an oil-in-water or water-in-oil emulsion, wherein there is used a particulate emulsifier comprising a responsive polymer wherein the stability of the emulsion is dependent on at least one environmental condition.
79. A method according to claim 78, wherein the particulate emulsifier has any one of the features of claims 1, 3 to 6, 9 to 14, and 16 to 52.
80. A method according to claim 78 or 79 wherein the emulsion is as claimed in any one of claims 53 to 55.
81. A method of breaking an emulsion comprising a particulate emulsifier, the particulate emulsifier comprising at least one polymer, the method comprising applying a stimulus to vary the hydrophilic/hydrophobic balance of the polymer to an extent sufficient to break the emulsion.
82. A method of breaking an emulsion comprising a particulate emulsifier, the particulate emulsifier comprising at least one polymer, the method comprising varying at least one environmental condition to an extent sufficient to break the emulsion.
83. A method according to claim 81 or 82, which comprises varying the temperature, pH, or ionic strength of the emulsion to an extent sufficient to break the emulsion.
84. A method of causing phase inversion of an emulsion comprising a particulate emulsifier, the particulate emulsifier comprising at least one polymer, the method comprising applying a stimulus to vary the hydrophilic/hydrophobic balance of the polymer to an extent sufficient to cause phase inversion.
■85. A method of causing phase inversion of an emulsion comprising a particulate emulsifier, the particulate emulsifier comprising at least one polymer, the method comprising varying at least one environmental condition to an extent sufficient to cause phase inversion.
86. A method according to claim 84 or 85, which comprises varying the temperature, pH, or ionic strength of the emulsion to an extent sufficient to cause phase inversion.
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