WO2011001036A1

WO2011001036A1 - Liquid-repellent material

Info

Publication number: WO2011001036A1
Application number: PCT/FI2010/050575
Authority: WO
Inventors: Hua Jin; Marjo PÄÄKKÖ; Olli Ikkala; Robin H. A. Ras
Original assignee: Aalto-Korkeakoulusäätiö
Priority date: 2009-07-02
Filing date: 2010-07-02
Publication date: 2011-01-06
Also published as: EP2449001A1; FI122230B; EP2449001A4; FI20095752A0; FI20095752A

Abstract

The present invention relates to surfaces with extremely repellency for liquids. The present invention provides an aerogel coated with at least one type of surface modifier, wherein the aerogel is superamphiphobic. The invention further provides a method for manufacturing said aerogel. The invention also provides a use of an aerogel in applications.

Description

LIQUID-REPELLENT MATERIAL

FIELD OF THE INVENTION

The present invention relates to surfaces with extreme repellency for liquids as well as to superamphiphobic aerogels that combine superhydrophobic and superoleophobic properties. More specifically the invention relates to a superamphiphobic aerogel. The present invention further relates to a method for manufacturing said aerogel. The present invention also relates to the use of said aerogel.

BACKGROUND OF THE INVENTION Surfaces that have extremely low affinity or extremely high repellency for water are superhydrophobic or super water repellent surfaces. They are known in the prior art and there exist many natural and artificial surfaces with superhydrophobicity (see e.g. Quere, Annu. Rev. Mater. Res. 38:71, 2008). Hydrophobicity of a material is determined by the contact angle of a water droplet on the surface. Several plants and animals incorporate superhydrophobic surfaces having water contact angle (CA) in excess of 150° thus providing materials scientists exciting models for functional biomimetic surfaces (Xia et al., Adv. Mater. 20: 2842, 2008). Classic examples are the leaves of Lotus-plant, the non-fogging compound eyes of mosquitoes, and the floating and locomotion of water striders on water surfaces (Xia et al., Adv. Mater. 20:2842, 2008; Quere, Annu. Rev. Mater. Res. 38:71, 2008; Bush et al., Annu. Rev. Fluid Mech. 38:339, 2006; Shi et al., Adv. Mater. 19:2257, 2007). Superhydrophobic coatings are disclosed in the previous patent literature, for example WO 2004/113456.

By contrast, extremely oil-repellent materials with contact angle (CA) in excess of 150° for oils, i.e., superoleophobic materials, are extremely rare and considerably more challenging to construct as the surface tension for oils is only a fraction of that of water. Feng and Jiang describe some principles (Adv. Mater. 2006, 18, 3063). The prior art discloses a few preparation methods for superoleophobic surfaces, based on oxidized aluminum surfaces, carbon nanotubes, lithographically patterned surfaces, electrospinning, and nanoparticles, that incorporate surface modifications (Shibuichi et al., J. Coll. Int. Sci. 208:287, 1987; Li et al., Angew. Chem. Int. Ed. 40: 1743, 2001; Xie et al., Adv. Mater. 16:302 2004; Yabu et al. Langmuir, 21 :3235, 2004; Tuteja et al., Science 318: 1618, 2007; WO 2009/009185). Most dirt is of an oily nature, and therefore it sticks easily on most surfaces, even on a superhydrophobic material. To have a material which is repellent for a large variety of dirt, it would need to be superamphiphobic, i.e. at the same time superhydrophobic and superoleophobic. The combination of superhydrophobicity and superoleophobicity is also termed as superlyophobicity or superomniphobicity. Such materials have low wettability for oils and water, are dirt repellent, self-cleaning and may also have reduced hydrodynamic drag. US patent application 2005/0181195 and international patent publication WO 2006/116424 disclose superamphiphobic surfaces. Said patent publications disclose fiber structures with desired wetting properties. However, there remain problems in large scale production and better concepts are called for. US patent application 2006/0110537 discloses an anti-fingerprint coating construction consisting of nano-composite material, which is hydrophobic, oleophobic or superamphiphobic.

Aerogel is a low-density and highly porous solid state material derived from a solvent swollen gel, i.e. percolative networks within a solvent medium, in which the liquid solvent phase has been replaced by air or gas without damaging the solid phase leaving a framework structure of substantially the same shape as the gel and without reducing the volume, or with only slightly reduced volume. This results in an extremely low density solid with remarkable properties. The aerogel porosities can vary widely, but they can be even 95-98%. In one preparation method, aerogels can be produced by extracting the liquid component of a solvent swollen gel, such as a hydrogel, through supercritical drying. The liquid is brought in a supercritical state and slowly drawn off without causing the solid matrix in the gel to collapse from capillary action. The first aerogels were produced from silica gels. Silica aerogels have a lattice structure consisting of amorphous silica (silicon dioxide, SiO₂). Liu et al. (Journal of Non-Crystalline Solids 354:4927-4931, 2008) have made superhydrophobic silica aerogels. US patent application 2004/0171700 discloses superhydrophobic silica aerogels treated with fluorine containing compounds. Carbon aerogels and alumina aerogels, chalcogels represent other forms of aerogels. In another preparation method, cellulose-based porous aerogels have been produced from aqueous gels by direct water removal by freeze-drying (Paakkό et al. Soft Matter 4:2192, 2008), which is an alternative to supercritical drying and reduces costs related to the production of aerogels. Patent applications DE 102006049179 and US 2008/0220333 as well as scientific articles by Gavillon and Budtova (Biomacromolecules 9(l) :269-277, 2008) and Jin et al. (Colloids Surf A 240:63-67, 2004) relate to other forms of cellulose aerogels in which the aerogel is made from solutions containing molecularly dissolved cellulose chains.

Aerogels have been used as thermal insulation and catalysts and catalyst supports, where their porosity and surface area make them especially useful. There are many instances where aerogels could be used to a greater extent. However, the known aerogels have disadvantages. Mechanical brittleness is also typical for most aerogels, i.e. they break into pieces, even when small stresses are applied. The prior art discloses that native nanocellulose aerogels with suppressed brittleness can be prepared (Paakkό et al. Soft Matter 4:2192, 2008). However, they are superamphiphilic, as they readily absorb water and oil and are thus superabsorbent.

Accordingly, there is a demand for facile concepts for superoleophobic, superamphiphobic, and dirt-repellent materials, and for aerogels with improved wetting properties. None of the prior methods disclose or anticipate that superoleophobicity or superamphiphobicity can be achieved from surface modified aerogels as a route for facile industrially applicable materials.

SUMMARY OF THE INVENTION

An object of the present invention is thus to provide a novel and inventive material and method therein so as to solve the problems presented by the prior art. The present invention relates to an aerogel coated with at least one type of surface modifier, wherein the aerogel is superamphiphobic. More specifically the aerogel comprises cellulosic material or silica, wherein the aerogel is superamphiphobic and gas-permeable.

The present invention also relates to a method for manufacturing an aerogel, wherein the method comprises steps of selecting material for preparing an aerogel from cellulosic material or from a metal oxide, such as silica, forming said material into an aerogel and treating the aerogel with a surface modifier to obtain a superamhiphobic aerogel. The present invention also relates to the use of said aerogel in anti-fouling of surfaces, filters, membranes, actuators, in packaging materials, in anti-fingerprint surfaces, in self-cleaning and dirt-repellent surfaces, as coatings for miniaturized sensors or other devices, in biochips, in floating devices such as superfast swimsuits, in oil tankers to prevent oil leakage, as thermal insulator in clothing, cooking ware, traffic, airplanes, boats and buildings, as weight support, as a material with low permittivity, as a selective membrane, as air filter, as gas-permeable carrier and in gas extraction from liquids.

Superhydrophobic aerogels have been made previously, mainly using silica aerogels. The present inventors surprisingly found out that superamphiphobic, gas permeable aerogels coated with a surface modifier could be produced. The aerogels of the present invention are the first aerogels that are superoleophobic or superamphiphobic and thus differ from the prior art. Especially, the superamphiphobic aerogel made from cellulose is the first one made from a biomaterial.

Aerogels are solids with a bicontinuous structure of which one of the phases is a gas such as air. Because the air or gas phase is continuous, the aerogels are highly porous, and the pores extend through the aerogel from one side to the other side. Because the aerogels mostly consist of air or gas, they have very low weight and low density. An additional potential benefit is that the continuous air phase stabilizes the Cassie-Baxter state of wetting. The aerogel of the present invention is an extremely light weight, highly porous material. Furthermore, it has large buoyancy i.e. large upward force when immersed in oil and water or their combinations. The aerogel also forms a plastron i.e. a thin layer of air when immersed in oil and water or their combinations.

The present inventors also surprisingly found out that the superamphiphobic, gas permeable aerogel coated with a surface modifier supports considerable weight not only on water surface but on oils.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 depicts SEM images of the native nanocellulose aerogel with robust network structuring at several length scales. The scale bars in the Figures IA and IB are 500 nm and 10 μm, respectively. Figure 1C shows a nanocellulose aerogel sheet of 2 cm in diameter and 0.5 mm in thickness. Nanocellulose aerogel sheets are flexible, which is very uncommon in relation to most aerogels.

Figure 2 depicts superamphiphobicity and load carrying capacity on liquid surfaces for native nanocellulose aerogel (2 cm in diameter) coated using (Tridecafluoro-1, 1,2,2- tetrahydrooctyl)trichlorosilane. Contact angles for paraffin oil (153°) and water (160°), respectively, are presented in center part of Figure 2, and show superoleophobicity and superhydrophobicity. The extreme repellency for oil and water is demonstrated by inserting said aerogel on oil or water surfaces, and demonstrating that the aerogels do not become wetted and do not sink by loading them by inserted weights (for example metal washers), even when the aerogels float several millimeters below the free liquid surfaces (see also Fig. 8). Side view photograph of an aerogel carrying the maximum weight as floating on paraffin oil and water, respectively, is shown in lower part of Figure 2. Contrast illumination allows visualization of the meniscus. The extreme liquid repellency manifests in the curvature of the liquids. The scale bars in the right are in mm.

Figure 3 illustrates the load carrying capacity on oil and water for the (Tridecafluoro- l,l,2,2-tetrahydrooctyl)trichlorosilane modified native nanocellulose aerogel (diameter

2 cm). The experimental data for paraffin oil (cubes) and water (diamonds) fit to a model calculating the upward force from the buoyancy and surface tension (line). The model takes into account the surface tension force around the perimeter of the aerogel disc, and also the buoyancy force, which equals the weight of the volume of the liquid replaced by the aerogel and the air.

Figure 4A illustrates dirt repellency for the (Tridecafluoro-1, 1,2,2- tetrahydrooctyl)trichlorosilane modified native nanocellulose aerogel. A drop of methylene green solution on unmodified native nanocellulose aerogel spreads rapidly. Figure 4B depicts that washing of non-fluorinated aerogel in water for 20 h does not remove the colour, but instead the aerogel disintegrates. Figure 4C depicts superamphiphobic (Tridecafluoro-ljl^^-tetrahydrooctyOtrichlorosilane modified native nanocellulose aerogel with a round drop of methylene green solution before washing. Figure 4D depicts that the methylene green can be easily washed away from the superamphiphobic aerogel demonstrating the dirt-repellent behaviour. Figure 5A depicts that unmodified native nanocellulose aerogel swells and disintegrates in water. Figure 5B depicts that superamphiphobic (Tridecafluoro- l,l,2,2-tetrahydrooctyl)trichlorosilane modified native nanocellulose aerogel kept in water overnight under rotation is stable.

Figure 6 depicts bottle-in-bottle setup for chemical vapour deposition (CVD) in one embodiment of surface modification of aerogels.

Figure 7 demonstrates gas permeability for the (Tridecafluoro-1, 1,2,2- tetrahydrooctyl)trichlorosilane modified native nanocellulose aerogel. Figure 7A depicts that a piece of pH-indicator paper was embedded between two superamphiphobic aerogel sheets and subsequently exposed to HCI vapour. The pH- indicator rapidly changed colour (one aerogel sheet was removed for clarity) showing that HCI vapour rapidly passed through the aerogel. Figure 7B depicts the original pH-indicator paper. Figure 8 depicts a setup to measure the load bearing of the aerogels on liquid (oil or water) surfaces. The weight of the metal washers is supported by the aerogel. It is notable that the washers have depressed the water surface to such large extent that the complete aerogel and all the washers are located below the free liquid surface.

Figure 9 demonstrates that superamphiphobic aerogels can carry devices floating on liquid surfaces. A primitive device was constructed by using a light emitting diode (LED) connected to a battery and emits red light. The total weight of the device is 3059.4 mg and it is sandwiched between two sheets of (Tridecafluoro-1, 1,2,2- tetrahydrooctyl)trichlorosilane modified native nanocellulose aerogel with dimensions 50 mm x 50 mm x 1 mm that allow floating on water. Figure 10 depicts that (Tridecafluoro-1, 1, 2, 2-tetrahydrooctyl)trichlorosilane modified native nanocellulose aerogel has metallic appearance due to the plastron on the aerogel surface immersed in paraffin oil (Figure 10A) and in water (Figure 10B). Light reflects efficiently at the air-liquid interface of the plastron. Figure 1OC depicts that the sample in air has a mat appearance because it only reflects light diffusively. Figure 11 depicts images of a water droplet (5 μl) bouncing on the superamphiphobic (Tridecafluoro-ljl^^-tetrahydrooctyOtrichlorosilane modified native nanocellulose aerogel. Each image was taken with an interval of 0.016 seconds. Such bouncing effect observed for superhydrophobic materials exemplifies their dirt- repellent nature. Figure 12 depicts a SEM image of the silica aerogel. The scale bar is 100 nm.

Figure 13A depicts water contact angle measured on silica aerogel, the contact angle is 161°. Figure 13B shows a 15 μl water droplet dropped on fluorinated silica aerogel surface with a tilt angle of 3.8° and its bouncing off from the surface in Figure 13C. The time interval between image in Figure 13B and Figure 13C was 0.02s. Figure 13D shows paraffin oil contact angle of 156° on fluorinated silica aerogel surface. Figure 13E shows a paraffin oil dropped on a tilted silica aerogel with tilt angle of 11.3°. The oil drop rolled off from the silica aerogel in Figure 13F. The time interval between Figure 13E and Figure 13F was 0.04s. Figure 14 depicts plastrons on the fluorinated silica aerogel when immersed in water (Figure 14A) and oil (Figure 14B).

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an aerogel, characterized in that the aerogel comprises a highly porous network composed of cellulosic material or metal oxides in air or gas, wherein the said aerogel is superamphiphobic due to at least one type of surface modifier, and the aerogel is permeable to gases due to its porosity. Examples of metal oxides include silica (=silicon dioxide), titanium dioxide, aluminium oxide, chromium oxide, vanadium oxide, zirconium oxide, iron oxide, magnesium oxide, lead oxide, nickel oxide, barium oxide, and mixed oxides incorporating two or more metal components. In the preferred embodiment, the aerogel comprises of nanocellulose whose method for manufacturing is facile and easy to scale-up in industry. The method can be used for manufacturing several types of aerogels. The surface modifier can be added onto the aerogel network using a multitude of methods using solution- or gas-based chemistries and different interactions between the surface modifiers and the aerogels, such as chemical reactivity, hydrogen bonding, coordination bonding, ionic bonding, pi-stacking, or combinations thereof. In the preferred embodiment, the surface modifiers are reacted with the aerogel using gas phase chemical vapour deposition which does not require organic solvents during the synthesis procedure, which is environmentally benign. In the most preferred embodiment, the surface modifiers with fluorinated chains and silane end groups are chemical vapour deposited with nanocellulose aerogels.

It has been surprisingly found that the aerogel of the present invention has a very low surface energy and that a liquid drop on the aerogel displays a very high contact angle.

Said superamphiphobic aerogels have many unexpected properties. The present inventors report for the first time aerogels with superamphiphobic properties and demonstrate their application for floating and load bearing on both oil and water. The inventors of the present invention demonstrate that aerogels treated with a surface modifier can become superoleophobic, superhydrophobic, and gas permeable membranes, and surprisingly support considerable weight not only on a water surface but even on oils with low surface tension. Such properties are valid also for oil and water mixtures, which is relevant for many technical applications. In other words the material is superamphiphobic i.e. at the same time oil and water repellent. Especially the inventors provide a flexible nanocellulose aerogel with superamphiphobic properties.

Superamphiphobic surfaces are appealing for e.g. anti-fouling, since purely superhydrophobic surfaces are easily contaminated by oily substances in practical applications, which in turn will impair the liquid repellency. No concepts have been previously shown for biomimetic floating and load bearing on oily liquids based on superoleophobicity. Still this is interesting for e.g. filtering, microfluidics, sensing, actuation, devices, and next-generation biomimetic microrobotics and autonomous devices sensing pollution on water of other chemical environments.

An advantage of the material of the present invention is that it is of extremely light weight, highly porous material, i.e. aerogel. The gas or vapour can go through the aerogel, but liquid not. The material has large buoyancy, i.e. large upward force when immersed in water. Unless otherwise specified, the terms, which are used in the specification and claims are understood to have the same meaning as commonly used in the art to which they pertain. For the purposes of the present invention, the following terms are defined herein :

The term "aerogel" refers to highly porous solid formed from a solvent swollen network gel, in which the liquid is replaced with a gas. In the most preferred embodiments the aerogel consists of more than 90% or even 98% gas, or, but in the present invention in some applications a lower density suffices, such as 50%.

The term "hydrogel" refers to a gel in which the liquid phase is water.

The term "nanocellulose" refers to very refined cellulose. Therein, the interconnected aerogel network has been substantially liberated from the macroscopic cellulose fibers and have dimensions of ca. 5 nm - 100 nm in the perpendicular direction in comparison to the local direction of the network skeleton (see Figure 1) and whose length can vary widely, up to several μms long or longer. In the present invention nanocellulose is cleaved down to ca. 5 nm diameter. The benefit in this process is that it retains the original native crystalline structure of cellulose, leading to good mechanical properties. Cellulose aerogel can also be made by a method, wherein cellulose is completely dissolved down to the individual polymer chains (Gavillon and Budtova, Biomacromolecules 9(l) :269-277, 2008 and Jin et al., Colloids Surf A 240:63-67, 2004). In this case the native crystalline cellulose structure does not remain.

The "contact angle" or "CA" is the angle at which the liquid/vapour interface meets the solid interface. The contact angle is specific for a given system and is determined by the interactions across the three interfaces. When a drop of a liquid rests upon a surface, it will spread out over the surface to a degree based upon such factors as the surface tensions of the liquid and the substrate, the smoothness or roughness of the surface, etc. The quantification of hydrophobicity or oleophobicity can be expressed as the degree of contact angle of the drop of the liquid on the surface.

Wetting of liquid droplets on surfaces is defined quantitatively by Young's equation :

θ

The contact angle θ depends on the interracial tension γ between the solid surface (s), liquid droplet (I), and gas (g). For example, when the contact angle between the water droplet and surface is small, the surface is hydrophilic. When the contact angle is large, but smaller than 150°, the surface is hydrophobic. When the contact angle is greater than 150°, the surface is superhydrophobic. Similar classification is valid for oil droplets, however, the definitions are oleophilic, oleophobic, and superoleophobic. The prefix "lipo-" is a synonym for the prefix "oleo-". Young's equation above is applicable when the substrate surface is smooth. However, when the substrate surface is rough, then such roughness must be taken into account in determining the contact angle θ* by Wenzel's equation : cos θ* = r cos θ where r = true surface area/apparent surface area (r > 1) representing the roughness factor of the surface. Contact angle is increased.

For surfaces that are rough enough so that air does become trapped between the substrate surface and the liquid (thus, forming a composite interface), Cassie's equation is used. In Cassie's equation, the contact angle θ* is determined by cos <9* = -l + φ_s (cos <9 + 1) where φ_s = top surface area of the "fakir need les"/appa rent surface area (φ_s << 1). Contact angle is much increased.

Those of skill in the art will be familiar with various means to measure the contact angle of various liquids on surfaces, e.g., with an optical contact angle meter, etc. Other measurements of super-liquidphobicity include contact angle hysteresis, advancing/receding contact angle, and sliding angle, e.g., the degree of angle or tilt of a substrate for a liquid drop to slide or move about on the substrate. Again, those of skill in the art will be quite familiar with such concepts and the necessary measurements needed. The term "superhydrophobicity" or "super water repellency" refers to a characteristic of a material that is extremely water-repellent i.e. repels aqueous or water-based liquids and causes a liquid drop on their surface to have a high water contact angle (CA), typically 150° or greater. A liquid drop can comprise a water or water based or aqueous drop. Superhydrophobic materials such as the leaves of the lotus plant have surfaces that are extremely difficult to wet.

The term "superoleophobicity" or "superlyophobicity" or "super oil repellency" or "superlipophobicity" refers to a characteristic of a material that is extremely oil- repellent and causes an oil drop or oil based drop on their surface to have a high contact angle (CA), typically in excess of 150°. Superoleophobic surfaces with contact angle of 150° or greater for oils are extremely rare and considerably more challenging to construct as the surface tension for oils is only a fraction of that of water.

The term "amphiphobicity" or "lyophobicity" or "omniphobicity" refers to a characteristic of a material that is at the same time hydrophobic and oleophobic and causes a liquid drop on their surface to have a contact angle (CA) typically greater than 90°.

The term "superamphiphobicity" or "superlyophobicity" or "superomniphobicity" refers to a characteristic of a material that is at the same time extremely superhydrophobic and superoleophobic and causes a liquid drop on their surface to have a high contact angle (CA), typically 150° or greater. In addition, also materials having a contact angle of 140° or greater are occasionally referred to as superamphiphobic materials [Sheen et al. Journal of Polymer Science: Part B: Polymer Physics, Vol. 46, 1984-1990 (2008)]. Superamphiphopbic materials have low wettability, are dirt repellent, self- cleaning and have reduced hydrodynamic drag. The term "plastron" refers to a thin layer of air which forms when super-repellent surfaces are immersed in water or oil. Plastron also refers to a gas cell to supply oxygen.

The term "self-cleaning" means that on superhydrophobic and superoleophobic surfaces a water droplet rolls along the inclined surfaces and collects on its way dirt, such as particles and greasy substances.

The term "surface modifier" means a surface-active agent or molecule capable of binding on the surface of the aerogel framework to modify its surface energy. They may vary widely, depending on the process and materials. A surface modifier molecule, intrinsically consists of two parts, i.e. the head and the tail, that are covalently connected. The tail yields a low surface energy. Low surface energy can be obtained with e.g. alkanes having several branches, thus containing several low energy -CH₃ groups but most preferably with fluorinated or semifluorinated chains. A head part facilitates the bonding to the aerogel network by chemical bonding or physical bonding, such as acid-base, ionic bonding, coordination bonding, hydrogen bonding, pi-stacking, or their combinations. For example, the aerogel framework can first be chemically modified to have anionic groups, such as carboxylates, sulphates, sulphonates, or phosphates and the like. In this case, the surface modifier can have cationic head groups, such as quaternary ammonium, pyridinium and the like to facilitate binding on the surface. The aerogel framework can be modified to have said cationic or basic chemical groups and the surface modifiers the matching anionic or acidic chemical groups. The surface modifier can be bound with hydrogen bonds and several matching hydrogen bonds, even by segments of DNA, and coordination chemistry, as well known in supramolecular chemistry. For example perfluorobutanesulfonic acid would bind to nanocellulose aerogel, once the nanocellulose would be modified to have basic amine groups. Certain higher molecular weight polymeric surface modifiers, such as fluorine-containing block copolymers, could bind taken the binding polymeric block is selected judiciously. Such a binding block could be the protein denoted as cellulose binding domain. A preferred embodiment deals with silanes with low surface energy tails. A general formula for the fluorinated silanes which can be used include

wherein R^a is a straight-chain or branched Qi_-24) fluorinated alkyl group, wherein the term "straight-chain or branched C_(I-24) alkyl group" includes preferably straight chain and branched fluorocarbons having 1 to 16, more preferably 1 to 12, more preferably 1 to 8 carbon atoms and most preferred 1 to 4 carbon atoms, such as methyl, ethyl, n- propyl, isopropyl, n-butyl and isobutyl groups.

R¹ is a lower alkyl group, such as a straight chain and branched fluorocarbons having 1 to 6 carbon atoms, preferably methyl, ethyl, propyl and isopropyl groups.

X¹ is a hydrolysable group, such as a halogen, such as fluoro or chloro, or an alkoxy group such as a straight chain or branched hydrocarbonoxy having 1 to 6 carbon atoms and n is 0 or 1,

X may represent the same or different groups.

Application of the surface modifier may comprise of a monolayer containing only one type of surface modifier or a mixed monolayer. The amount of surface modifier is a full monolayer, the reaction is self-terminating because only one layer of molecules can react with the aerogel surface. The full monolayer is needed to shield the underlying cellulose surface from the liquid, and to maximize the surface density of surface modifier leading the low surface energy. A mixed monolayer means that the monolayer contains two different kinds of surface modifier molecules. The mixed monolayer is also called a binary monolayer (Fadeev and McCarthy, Langmuir 25(21) :7238-7243, 1999). First, a monolayer of a bulky surface modifier is made followed by the filling of the remaining cavities with a smaller sized surface modifier.

An object of the present invention is to provide an aerogel, which is coated with at least one type of surface modifier characterized in that the aerogel is superamphiphobic. The aerogel of the invention is superamphiphobic and thus water and oil repellent due to at least one type of surface modifier but still gas-permeable.

In a preferred embodiment the aerogel comprises a cellulose network which has been substantially refined so that the smallest cellulose dimension perpendicular to the local network skeleton direction is less than 500 nm, preferably less than 100 nm. In a preferred embodiment the aerogel comprises cellulose, preferably cellulose fines, most preferably nanocellulose. Other naturally occurring polysaccharides or sugar polymers, such as chitosan and chitin can be used.

In one embodiment the aerogel comprises a metal oxide. Examples of metal oxides include silica (=silicon dioxide), titanium dioxide, aluminium oxide, chromium oxide, vanadium oxide, zirconium oxide, iron oxide, magnesium oxide, lead oxide, nickel oxide, barium oxide, and mixed oxides incorporating two or more metal components.

The cellulose aerogel of the present invention is flexible.

The aerogel can be of any size or shape. The aerogel can also be chemically pre- modified to facilitate interaction with a surface modifier.

The aerogel of the present invention has a defined porosity and a liquid drop or liquid on the aerogel displays a defined contact angle.

In a preferred embodiment of the invention the aerogel of the present invention has a defined porosity of at least 50%, preferably at least 70%, preferably at least 80%, preferably at least 90%, more preferably at least 95%, such as 98%.

The aerogel of the present invention is a highly porous material with density of typically from 0.002 to 1 g/cm³, preferably 0.01 g/cm³. For comparison the density of air is 0.0013 g/cm³.

In an embodiment of the invention a liquid drop comprising paraffin oil, engine oil, silicon oil, organic solvents such as alkanes, aromatic compounds and their derivatives, or water or their mixtures on the aerogel displays a defined contact angle of at least 140°, preferably at least 150°, more preferably at least 160°, more preferably at least 170°. Also water/oil mixtures, a water based liquid, or an aqueous liquid are included. In a preferred embodiment of the invention a paraffin oil liquid drop on the aerogel displays a defined contact angle of at least 140°, preferably at least 150°, more preferably at least 160°, more preferably at least 170°. An example is that when a mineral oil droplet is applied on the (tridecafluoro-1, 1,2,2- tetrahydrooctyl)trichlorosilane (FTCS) nanocellulose aerogel surface, the contact angle is 158°. A water droplet on the surface of FTCS-nanocellulose aerogel i.e. nanocellulose aerogel treated with FTCS gives a static contact angle of 160° (See Table 1). In a preferred embodiment the cellulosic material is from plant cells, wood, non-wood material or recycled fibers, but is not restricted to these. Wood can be from softwood tree such as spruce, pine, fir, larch, douglas-fir or hemlock, or from hardwood tree such as birch, aspen, poplar, alder, eucalyptus or acacia, or from mixture of softwoods and hardwoods. Non-wood material can be from for example plant substances such as grasses, leaves, seeds, straw, bark, hulls, fruits or vegetables, agricultural residues, algae, fungi or of bacterial origin.

The aerogel of the present invention is coated with at least one type of surface modifier. In an embodiment of the present invention a surface modifier contains one part which yields a low surface energy, such as fluoroalkanes, and another part which binds to the aerogel surface, such as a silane. In a preferred embodiment the surface modifier contains a monolayer of a surface modifier. The surface modifier may comprise of a monolayer containing only one type of surface modifier or a mixed monolayer. The surface modifier may contain fluoro- atoms. The use of a second type of surface modifier in a binary monolayer has an effect on the contact angle (Langmuir 1999, 15, 7238-7243). Examples of the compounds which are capable of use in the present invention as surface modifiers are listed below. Such listed examples are only for illustrative purposes and should not be taken as limiting to the invention. Particularly preferred examples of silanes are fluorosilanes, more preferably (tridecafluoro-1, 1,2,2- tetrahydrooctyl)trichlorosilane (FTCS). Other suitable silanes include but are not restricted to trichloromethylsilane (TCMS), trichloroethylsilane, trichloro(n- propyl)silane, trimethoxymethylsilane, triethoxymethylsilane, (3-phenylpropyl)- methyldichlorosilane (PMDS), benzyltrichlorosilane, methylbenzyl-trichlorosilane, trifluoromethylbenzyltrichlorosilane, methyltriethoxysilane, (3-phenylpropyl)- methyldimethoxysilane, (3-phenylpropyl)-methyldiethoxysilane, tris(trimethylsiloxy) chlorosilane (Tris-TMSCI), tris(trimethylsiloxy)silylethyldimethylchlorosilane and bis(trimethylsiloxy)methylsilylethyldimethylchlorosilane.

The present invention also relates to a method for manufacturing an aerogel which is coated with at least one type of surface modifier, wherein the method comprises steps of selecting material for preparing an aerogel from cellulosic material or a metal oxide, forming said material into an aerogel and treating the aerogel with a surface modifier to obtain a superamphiphobic aerogel. Examples of metal oxides include silica (=silicon dioxide), titanium dioxide, aluminium oxide, chromium oxide, vanadium oxide, zirconium oxide, iron oxide, magnesium oxide, lead oxide, nickel oxide, barium oxide, and mixed oxides incorporating two or more metal components. The treatment with a surface modifier can be carried out at any process step.

In a preferred embodiment of the invention the method for manufacturing the aerogel comprises steps of preparing a suspension comprising cellulosic material, subjecting the suspension to enzymatic and/or mechanical disintegration to obtain nanocellulose gel, forming said nanocellulose gel to obtain a superamphiphobic nanocellulose aerogel.

In an embodiment of the invention the surface modifier is provided by chemical vapour deposition or liquid phase deposition.

In a preferred embodiment of the invention the disintegration of the fiber suspension is carried out with a friction grinder or fluidizer such as microfluidizer, macrofluidizer or fluidizer-type homogenizer to obtain nanocellulose gel. Preferably, nanocellulose is obtained by cleaving cellulosic material into networks with lateral dimensions of ca. 5 nm. In another preferred embodiment the cellulose is dissolved completely to the individual polymer chains. The surface modifier can be reacted with the aerogel by bringing the surface modifier solution in contact with the aerogel. Chemical vapour deposition (CVD) does not require solvents i.e. it is thus more environmentally benign. If the solvent is used in the method the removal of the solvent from the aerogel may result in capillary forces which can lead to deformation or even collapse of the aerogel. Comparisons of CVD and liquid phase deposition have shown that the contact angle of CVD treated surfaces is a little higher, probably due to a better packing of surface modifier (higher surface modifier density) in CVD. Both CVD and liquid phase deposition lead to similar wettability properties. Liquid phase deposition is also called solution phase deposition or solution phase reaction. The present invention also relates to the use of the present aerogel in anti-fouling of surfaces, filters, and actuators, and membranes, in packaging materials, in anti- fingerprint surfaces, in self-cleaning and dirt-repellent surfaces, as coatings for miniaturized sensors and other devices, in biochips. The present aerogel can be used in floating devices such as superfast swimsuits and in oil tankers to prevent oil leakage. The applications of the present aerogel include the use as thermal insulator for example in clothing, cooking ware, traffic, airplanes, boats and buildings. The aerogel can be used as a selective membrane; liquids such as water cannot go through the membrane but vapours and gases can. The aerogel can be used as an air filter to remove solid particles from air, as weight support, as gas-permeable carrier and in gas extraction from liquids.

The present inventors demonstrate that flexible, nanocellulose aerogels treated with a surface modifier, such as fluorosilane are superoleophobic, superhydrophobic, and gas permeable membranes, support considerable weight not only on a water surface but even on oils with low surface tension. The weight support is achieved by surface tension acting at different length scales: at the macroscopic scale along the perimeter of the carrier, and at the microscopic scale by preventing soaking of the aerogel thus ensuring buoyancy. In addition, the superoleophobicity leads to the first demonstration of a thin layer of air at the aerogel surface when immersed in a nonaqueous medium, mimicking the plastron used by some insects and spiders for underwater-respiration.

When some weight load is added to the aerogel of the present invention, while floating on a liquid like water or oil, the aerogel depresses the liquid surface, but does not sink. This demonstrates superoleophobicity and superhydrophobicity. Aerogel of the present invention provides coating to materials, which would otherwise sink without such a coating.

Another property of the superamphiphobic aerogel is the plastron when immersed in oil or water liquid. A plastron is a thin layer of air which shields the aerogel from the liquid. In other words there is a gas cell to supply oxygen. Certain aquatic organisms like insects or spiders also have a plastron in water, and they use it for breathing underwater. Therefore the aerogel of the present invention has biomimetic properties. The present inventors report the first observation of a plastron in a non-aqueous liquid. Obviously the plastron is present in water and in oil because the aerogel has both oil- and water-repellent properties.

The aerogel carrier mimics the water strider by following common features but surprisingly extends to concepts from pure water to oils and mixtures of oils and water: (a) load carrier on oil and water liquid surfaces, (b) superoleophobicity, (c) structures ranging from the nanoscale to the micronscale, (d) plastrons in oil and water liquids, i.e. thin layer of air at the surface of the immersed aerogel (Fig. 10B) and (e) flexibility. The flexibility of the water strider legs and of the aerogel is beneficial for the supporting ability by adapting their shape and thus preventing early piercing the liquid surface. Importantly, the aerogel has additional attractive features including (a) larger supporting force by combining buoyancy and surface tension, (b) cargo weight allowed up to 99,6% of maximum supporting force due to ultra light weight of aerogel, (c) gas permeability (Fig. 7A) and (d) balance without further assembly. A single water strider leg cannot carry a load on top of water, because the leg would rotate dropping the load in the water. Therefore, to keep balance, the water strider and its robotic counterparts need multiple legs assembled to a rigid body. The advantage of the aerogel, compared to water strider legs, is that it keeps itself in balance without any additional assembly steps.

The present invention opens up a new platform for carriers or for coatings which have large load-bearing capability on various organic liquids including oil-polluted water, and are at the same time foul-resistant and gas-permeable membranes, applicable e.g. as coatings for miniaturized robots or future environmental gas sensors floating on practical liquids.

Application areas of the aerogel of the present invention include, but are not restricted to use in anti-fouling of surfaces, filters, actuators, and membranes, in packaging materials, in anti-fingerprint surfaces, in self-cleaning and dirt-repellent surfaces, in biochips, as thermal insulator in clothing, cooking ware, traffic, airplanes, boats and buildings, as weight support, as gas-permeable carrier, in oil repellent structures, in composites and conductors, as coating to materials which would normally sink to provide weight support, as material with low permittivity. The present aerogel can be used in anti-fouling of surfaces in boats instead of antifouling paints. The growth of micro-organics is prevented. The aerogel can be also used in flow resistance in boats and other objects.

The aerogel of the present invention can be used while obtaining fresh water from the sea water. The plastron is useful for gas extraction from liquids, for example for immersed fuel cells. Reduced hydrodynamic drag and buoyancy of the present aerogel make it useful in superfast swimsuits or other floating devices. The present aerogel can be utilized in oil tankers having a double wall with air in between to prevent oil leakage in case one wall would break.

Also applications in the forest industry can utilize the aerogel of the present invention. The invention is now discussed in more detail using the following non-limiting examples. Example 1

Materials and Methods

Preparation of the nanocellulose hydrogel The pulp used in refining to prepare a nanocellulose hydrogel was a commercial never- dried ECF-bleached birch kraft pulp from UPM-Kymmene Oyj, Finland. The pulp suspension was diluted to 3 % consistency and cellulose nanofibrils were disintegrated using an ultra-fine friction grinder (Masuko Supermass colloider®, model MKZA 10-15J). The method of preparation is not critical as related results are obtained using microfluidization to cleave the large cellulose fibers to nanocellulose. The grinder consists of lower rotating and upper stationary SiC grinding stones (gap 100 μm). During grinding the power consumption was kept at levels 3.2 - 3.8 kW. Pulp suspension was recirculated in the grinder five times. The solids content of the nanocellulose gel was 1.3%.

Preparation of the nanocellulose aerogel

In order to promote dispersion, the aqueous hydrogel was magnetically stirred for one day. The mould for the aerogel was a press-to-seal silicone isolator (Grace Bio-Labs Inc.) on a glass slide. Aerogels with various sizes and thicknesses were prepared, for example a disc with diameter 20 mm and thickness 0.5 mm, and a square of 50 mm x 50 mm and thickness 1.0 mm. In principle any aerogel size and shape can be made. In one embodiment, the mould was filled with the aqueous gel and transferred in a vacuum oven for vacuum drying at room temperature. At first, due to evaporation, the aqueous gel cools down and freezes typically within a few minutes. The gel freezes because the evaporating water molecules consume heat of evaporation. Once the sample was frozen, water was removed by sublimation. When the pressure reached 3xlO^"2 mbar, the aerogel was ready. The time for reaching this pressure depends on the volume of the gel and also on the number of samples in the vacuum oven. For example for one sample with diameter 20 mm and thickness 5 mm, the drying time is approximately 2 hours. More samples or larger volume of gel require more time. Other procedures for making the aerogel are described in Paakkό et al., Soft Matter 4, 2492 (2008). The silica aerogel

The silica aerogel was purchased from Airglass (Airglass AB, Staffanstorp, Sweden; www.airglass.se).

Surface modification of an aerogel by chemical vapour deposition (CVD) The aerogel was placed in a 30 ml glass bottle. 200 μl (Tridecafluoro-1, 1,2,2- tetrahydrooctyl)trichlorosilane (FTCS) (97%, ABCR) was inserted in a 2 ml glass bottle. This 2 ml glass bottle was placed in the above mentioned 30 ml bottle (see Fig. 6 for the "bottle-in-bottle" setup). This "bottle-in-bottle" setup is designed to avoid direct contact between aerogel and liquid FTCS. Finally, the 30 ml bottle was sealed with a cap and placed in an oven at 70°C for 2 h. To remove unreacted silanes, the aerogel was kept in a vacuum oven until the vacuum level reached 3xlO^"2 mbar or less. Various fluorosilanes were tested (Table 1).

Table 1. Water contact angles of nanocellulose aerogel coated by chemical vapour deposition (CVD) with various fluorosilane compounds.

Compound Water contact angle

(Tridecafluoro-1, l,2,2-tetrahydrooctyl)trichlorosilane (FTCS) 160

(Bis(tridecafluoro-1, 1,2,2- 138° tetrahydrooctyl)dimethylsiloxy)methylchlorosilane

(Tridecafluoro-ljl^^-tetrahydrooctyOdimethylchlorosilane 133°

(Heptadecafluoro-ljl^^-tetrahydrodecyOdimethylchlorosilane 126°

Surface modification of an aerogel in solvent phase

200 μl (Tridecafluoro-1, 1, 2, 2-tetrahydrooctyl)trichlorosilane (FTCS) was dissolved in 2 ml dry toluene and mixed for 1 h. A piece of nanocellulose aerogel was immersed in the FTCS solution The solution penetrates in the aerogel completely, without disintegration of the aerogel. After 1 h, the aerogel was taken out of the solution and placed in dry toluene to wash away the unreacted FTCS. After 15 minutes, the aerogel was washed a second time by placing in a beaker of fresh dry toluene. Next, the aerogel was taken out of the toluene and placed in the hood and subsequently in the vacuum oven to evaporate the remaining toluene. This lead to high water and oil contact angle. The method of applying the surface modifier is not critical and both gas and liquid phase chemistries can be used. Example 2

Scanning electron microscope (SEM) images of a nanocellulose aerogel

The nanocellulose aerogel is a highly porous material with density of 0.01 g/cm³ and porosity of 98%. SEM images showed a highly entangled network of nanoscopic fibrils, with hierarchical porous structures from the nano to micro scale in nanocellulose aerogel (Fig . IA and ID) . The pore distribution was 37% and 57% in 2-

10 nm and 10-50 nm respectively. The untreated nanocellulose aerogel was superamphiphilic; it absorbed water and mineral oil in less than 0.064 seconds and is thus a superabsorbent. This is due to the combination of amphiphilic properties of cellulose and large surface area caused by large porosity. SEM analysis was carried out with JEOL JSM-7500F Scanning Electron Microscope.

Example 3

Surface modification of an aerogel by chemical vapour deposition (CVD)

After chemical vapour deposition (CVD) by (Tridecafluoro-1, 1,2,2- tetrahydrooctyl)trichlorosilane (FTCS), nanocellulose aerogel became superoleophobic and superhydrophobic: A 5 μl mineral oil droplet was applied on the FTCS-nanocellulose aerogel surface, and the contact angle was 158°. A water droplet ( 10 μl) on the surface of FTCS-nanocellulose aerogel gave a static contact angle of 160°. Fig. 11 shows images of a water droplet (5 μl) bouncing on the superamphiphobic aerogel. Each image was taken with an interval of 0.016 seconds. Such bouncing effect observed for superamphiphobic materials exemplifies their dirt- repellent nature.

Example 4 Load bearing capability of an aerogel

The aerogel is a network composed of nanosized cellulose nanofibrils and their micronsized aggregates leading to hierarchies (Fig. 1) fluorinated using (tridecafluoro- l,l,2,2-tetrahydrooctyl)trichlorosilane (FTCS) by chemical vapour deposition (CVD). The aerogel was flexible and superamphiphobic with a CA of 153° and 158° for paraffin oil and mineral oil, and 160° for water (Fig. 2). Even though the aerogel is highly porous (porosity 98%), the super-repellency prevents water and oil to enter the pores. The load bearing capability of the aerogel on oil and water were inspected (Fig. 2). On oil, an aerogel with a mass of 3.0 mg and diameter 19 mm could bear a maximum load of 960 mg, and made a dimple of 4.3 mm depth without sinking. Correspondingly, on water the aerogel could carry a maximum load of 1658 mg with a dimple of 4.6 mm. The data could be fitted by a model comprising buoyancy and surface tension along the perimeter of the disc (Fig. 3). The surface tension acts on the aerogel carrier at different length scales: a macroscopic surface tension along the perimeter of the disc, and a microscopic surface tension around each fibril preventing the liquid from penetrating the aerogel, and thus maintaining the buoyancy.

Example 5

Aerogel stability and dirt-repelling properties

A non-fluorinated cellulose aerogel (Fig. 5A) and fluorinated superamphiphobic aerogel (Fig . 5A) were kept in water overnight, for several hours under rotating . The non-fluorinated aerogel absorbed water and swelled, and when it was gently agitated by rotation, it fell apart into many pieces. On the other hand the superamphiphobic aerogel stayed floating on the water. In other words, it did not swell and the aerogel did not change in shape nor got disintegrated. The superamphiphobic properties tremendously improved the aerogel stability in water. The dirt-repelling properties of the cellulose aerogel were demonstrated by using ink, i.e. an aqueous solution of methylene green. When an ink droplet was placed on non- fluorinated aerogel (Fig. 4A), the droplet became rapidly absorbed, making the aerogel strongly coloured. Rinsing with water after 1 min could not remove the ink. Even when the sample was immersed in water for 20 h, followed by rinsing, it remained coloured and in addition aerogel was desintegrated into gelly clods (Fig. 4B). The dye molecules were strongly adsorbed on the native cellulose surface. In contrast, when the ink was placed on the superamphiphobic aerogel, it formed a round droplet, and did not wet the surface (Fig. 4c). The methylene green droplet was easily washed away from the superamphiphobic aerogel (Fig. 4d), which clearly showed that the FTCS-treated cellulose aerogel had self-cleaning, dirt- repelling properties. Example 6 Plastron

The presence of the plastron was seen from the metallic appearance when viewed under a grazing angle. There was a metallic appearance due to the plastron on a superamphiphobic cellulose aerogel in paraffin oil (Fig. 10A) and water (Fig. 10B). Light reflected efficiently at the air-liquid interface of the plastron. The aerogel in air had a mat appearance and reflected light only diffusely (Fig. 10C).

Example 7 Contact angles on different materials

The contact angles of water and oil droplets on different materials were measured: the nanocellulose aerogel of the present invention, silica aerogel, fines made from pulp, and filter paper.

Table 2. Contact angles on different materials.

Fines and filter paper are forms of cellulose. Fines had a broad size distribution from about 20 nm to several micron. Filter paper contains structures from the micron to tens of micron scale. Fines allows to make a superoleophobic or superamphiphobic surface. Filter paper allows to make a superhydrophobic surface and an oleophobic surface, but not a superoleophobic or superamphiphobic surface. The experiment showed that nanoscopic structures are essential for achieving superoleophobicity or superamphiphobicity.

Example 8

Superamphiphobic silica aerogel Silica aerogel is an ultralightweight and highly porous solid material with nanoscopic features (Fig. 12). The fluorinated silica aerogel was superamphiphobic, with a water contact angle of 161° (Fig. 13Aa) and a mineral oil contact angle of 156° (Fig. 13D). The silica aerogel had self-cleaning properties as water and oil droplets were easily removed from the surface by tilting the sample (Fig. 13B and 13C) for water; Fig 13E and 13F for oil). The plastron, i.e. the thin layer of air on the surface of an immersed liquid-repellent sample, was present on the fluorinated silica aerogel immersed in water (Fig. 14A) and in oil (Fig. 14B), as could be observed from the mirror-like appearance. This silica aerogel sample showed that the superamphiphobic effect observed for fluorinated cellulose aerogels is applicable for fluorinated aerogels in general and can be extended to a wide range of materials, as long as they are fluorinated and have a very open porous nanostructure.

REFERENCES:

Bush et al., Annu. Rev. Fluid Mech. 38:339, 2006

Fadeev and McCarthy, Langmuir 25(21):7238-7243, 1999

Feng and Jiang, Adv. Mater. 18:3063, 2006

Gavillon and Budtova, Biomacromolecules 9(l) :269-277, 2008

Jin et al., Colloids Surf A 240:63-67, 2004

Li et al., Angew. Chem. Int. Ed. 40: 1743, 2001

Liu et al. Journal of Non-Crystalline Solids 354:4927-4931, 2008

Paakkό et al., Soft Matter 4:2192, 2008

Quere, Annu. Rev. Mater. Res. 38:71, 2008

Sheen et al., Journal of Polymer Science: Part B: Polymer Physics, Vol. 46, 1984-1990, 2008

Shi et al., Adv. Mater. 19:2257, 2007

Shibuichi et al., J. Coll. Int. Sci. 208:287, 1987

Tuteja et al., Science 318: 1618, 2007

Xia et al., Adv. Mater. 20:2842, 2008

Xie et al., Adv. Mater. 16:302 2004

Yabu et al., Langmuir, 21 :3235, 2004

DE 102006049179, WO 2004/113456, WO 2006/116424, WO 2009/009185

USSN 2004/0171700, USSN 2005/0181195, USSN 2006/0110537, USSN 2008/0220333

Claims

1. An aerogel coated with at least one type of surface modifier, characterized in that the aerogel is superamphiphobic.

2. The aerogel according to claim 1, characterized in that the aerogel comprises cellulose.

3. The aerogel according to any of the preceding claims, characterized in that the aerogel comprises a cellulose network which has been refined so that the smallest cellulose dimension perpendicular to the local network skeleton direction is less than 500 nm.

4. The aerogel according to any of the preceding claims, characterized in that the aerogel comprises a cellulose network which has been refined so that the smallest cellulose dimension perpendicular to the local network skeleton direction is less than 100 nm.

5. The aerogel according to claim 1, characterized in that the aerogel comprises a metal oxide, such as silica.

6. The aerogel according to any of the preceding claims, characterized in that a liquid drop comprising paraffin oil, engine oil, silicon oil, organic solvents such as alkanes, aromatic compounds and their derivatives, or water or their mixtures on the aerogel displays a defined contact angle of at least 140°.

7. The aerogel according to any of the preceding claims, characterized in that a liquid drop comprising paraffin oil, engine oil, silicon oil, organic solvents such as alkanes, aromatic compounds and their derivatives, or water or their mixtures on the aerogel displays a defined contact angle of at least 150°.

8. The aerogel according to any of the preceding claims, characterized in that a liquid drop comprising paraffin oil, engine oil, silicon oil, organic solvents such as alkanes, aromatic compounds and their derivatives, or water or their mixtures on the aerogel displays a defined contact angle of at least 160°.

9. The aerogel according to any of the preceding claims, characterized in that a liquid drop comprising paraffin oil, engine oil, silicon oil, organic solvents such as alkanes, aromatic compounds and their derivatives, or water or their mixtures on the aerogel displays a defined contact angle of at least 170°.

10. The aerogel according to any of the preceding claims, characterized in that a paraffin oil liquid drop on the aerogel displays a defined contact angle of at least 140°.

11. The aerogel according to any of the preceding claims, characterized in that a paraffin oil liquid drop on the aerogel displays a defined contact angle of at least 150°.

12. The aerogel according to any of the preceding claims, characterized in that a paraffin oil liquid drop on the aerogel displays a defined contact angle of at least 160°.

13. The aerogel according to any of the preceding claims, characterized in that a paraffin oil liquid drop on the aerogel displays a defined contact angle of at least 170°.

14. The aerogel according to any of the preceding claims, characterized in that the surface modifier is a compound that contains at least one part, which provides a low surface energy and at least one part, which binds to the aerogel surface.

15. The aerogel according to any of the preceding claims, characterized in that the surface modifier contains a silane group.

16. The aerogel according to any of the preceding claims, characterized in that the surface modifier contains a silane group and a fluorinated group.

17. The aerogel according to any of the preceding claims, characterized in that the surface modifier comprises (tridecafluoro-l,l,2,2-tetrahydrooctyl)- trichlorosilane.

18. The aerogel according to any of the preceding claims, characterized in that the aerogel has a defined porosity of at least 50%.

19. The aerogel according to any of the preceding claims, characterized in that the aerogel has a defined porosity of at least 70%.

20. The aerogel according to any of the preceding claims, characterized in that the aerogel has a defined porosity of at least 80%.

21. The aerogel according to any of the preceding claims, characterized in that the aerogel has a defined porosity of at least 90%.

22. The aerogel according to any of the preceding claims, characterized in that the aerogel has a defined porosity of at least 95%.

23. A method for manufacturing an aerogel, characterized in that the method comprises steps of

selecting material for preparing an aerogel from cellulosic material, or from a metal oxide, such as silica;

- forming said material into an aerogel; and

treating the aerogel with a surface modifier ;

to obtain a superamphiphobic aerogel.

24. The method according to claim 23, characterized in that the method comprises steps of

- preparing a suspension comprising cellulosic material;

subjecting the suspension to enzymatic and/or mechanical disintegration to obtain nanocellulose gel, or to complete dissolution to obtain a cellulose solution;

forming said nanocellulose gel into an aerogel; and

- treating the aerogel with a surface modifier;

to obtain a superamphiphobic nanocellulose aerogel.

25. The method according to claim 23 or 24, characterized in that the aerogel is treated with the surface modifier by a gas phase chemical vapour deposition or a liquid phase deposition.

26. The method according to claims 23 to 25, characterized in that the surface modifier is silane, preferably fluorosilane, more preferably (tridecafluoro- l,l,2,2-tetrahydrooctyl)trichlorosilane.

27. Use of an aerogel according to any of the preceding claims in anti-fouling of surfaces, filters, membranes, actuators, in packaging materials, in anti- fingerprint surfaces, in self-cleaning and dirt-repellent surfaces, as coatings for miniaturized sensors, in biochips, in floating devices such as superfast swimsuits, in oil tankers to prevent oil leakage, as thermal insulator in clothing, cooking ware, traffic, airplanes, boats and buildings, as weight support, as a selective membrane, as air filter, as low-permittivity material, as gas- permeable carrier and in gas extraction from liquids.