WO2021170981A1

WO2021170981A1 - Ionic liquid surface coatings

Info

Publication number: WO2021170981A1
Application number: PCT/GB2021/050427
Authority: WO
Inventors: Mark Gilmore; Ross Savage; Steven Bell; Peter Nockemann; Callum Robinson
Original assignee: Kilwaughter Minerals Limited
Priority date: 2020-02-25
Filing date: 2021-02-19
Publication date: 2021-09-02
Also published as: EP4110745A1; GB202002665D0; GB2592383A

Abstract

The present invention relates to a water repellent material comprising a substrate and an ionic liquid based coating, as well as methods of forming such water repellent materials. In addition, the present invention relates to liquid dispersions comprising ionic liquids for use in forming water repellent coatings.

Description

IONIC LIQUID SURFACE COATINGS

Field of the Invention

Background of the Invention

Materials commonly used in construction, such as metals, concrete, clay, wood, stone and polymeric based materials, often come into contact with corrosive substances, for example acid rain, which can cause physical and structural damage to these materials, leading to the need for replacement or repair.

Acid rain is formed when air pollutants, such as nitrogen oxide, sulphur dioxide and sulphur trioxide react with water within the atmosphere, resulting in the formation of strong acids such as nitric acid, sulphurous acid and sulphuric acid. The acids formed then precipitate to earth as rain or snow, thereby contacting buildings and/or infrastructure. Acid rain is known to cause weathering of stone by dissolving calcium-based components therein. In addition, acid rain may corrode metals, such as bronze, copper, nickel, zinc and certain types of steel. Further still, acid rain can reduce the adhesion of painted surface coatings, causing peeling.

Water is also known to cause structural damage to at least some of the above mentioned materials. For example, porous materials, such as bricks and mortar, can undergo severe structural damage as a result of the freeze-thaw cycles of water contained within the pores of the material. As water expands during freezing, the brick or mortar may be fractured. Alternatively, sections of the material may break away due to the expanding volume of the freezing water.

In addition, as many of the materials used in construction are porous, water may penetrate the outer surfaces of buildings and/or infrastructure leading to damp. Typical sources of moisture which may penetrate through construction materials include rainwater, groundwater, plumbing, construction water, condensation and both the internal humidity of the building as well as the humidity of the surrounding environment. Extended periods of damp can lead to the physical or chemical deterioration of the internal and/or external structure of the building, for example the deterioration of plaster or masonry as well as timber decay. In addition, continued moisture on the surface of or throughout construction materials can enable microbial growth on the inner and/or outer surfaces of buildings. Where microbial growth occurs on the internal structure of the building, this can lead to adverse health effects for inhabitants.

Furthermore, where microbial growth occurs on the internal or external surfaces of buildings, biodeterioration of construction materials can occur through chemical and mechanical processes. Microbes are known to excrete organic and/or inorganic acids as a by-product of the type of metabolic process it undergoes. These acids can then solubilise part of the materials upon which the microbes grow (for example the acid produced can dissolve minerals present in stone). In addition, growth of microbes on the surface of construction materials can lead to damage through mechanical biodegradation. With particular respect to the external surfaces of buildings and infrastructure, it is known that air pollution (containing compounds such as nitrogen dioxide (NO₂) and sulphur dioxide (SO₂)) can act as a further source of nutrients, accelerating the growth of microbes and therefore the rate at which deterioration occurs.

Further, it is understood that structures which retain water/moisture within or on their external surfaces transmit heat faster compared to buildings/infrastructure having dry external surfaces, thereby increasing the required energy consumption for residents within these structures.

A further issue can arise when metal surfaces, such as copper, cast iron and galvanised steel react with oxygen within water to form metal oxides (for example, producing rust on iron, tarnish on silver, and verdigris on copper or brass). Over time, the continued formation of metal oxides results in the creation of pits and/or cracks within the metal surface, weakening the metal structure and often resulting in structural failure. In addition, minerals present within water can be deposited on the inner surface of metal plumbing, wherein these minerals can also corrode the metal surface. Pinhole corrosion in metal pipework can lead to small amounts of water leaking from the pipe.

Due to the potential corrosion of structural materials, it is common practice to protect the material surface by applying a water repellent coating. Known water repellent coatings for materials such as concrete are based on silanes and siloxanes, or similar materials such as sodium silicate, silicone resin solution, silane/siloxane, silane/siloxane with an acrylic topcoat, alkylalkoxysilane, two component acrylics, silicone in turpentine, siloxane acrylic, thixotropic cream (based on octyltriethoxysilane), water based solutions of alkylalkoxysilane, and acrylic latex (such as discussed in “The Effectiveness of Silane and Siloxane Treatments on the Superhydrophobicity and lcephobicity of Concrete surfaces", Sunil M. Rao, The University of Wisconsin-Milwaukee, 2013). Such coatings can also be used to form a waterproof surface on masonry, limestone and wood. Alternatively, sheet- applied membranes, such as urethane-based membranes or synthetic rubbers, such as neoprene and hypalon, may be used to provide a waterproof coating layer.

Natural hydrophobic materials, such as waxes, for example beeswax and lanolin (as discussed in “Comprehensive view of chemistry, manufacturing & applications of lanolin extracted from wool pretreatment’ Sengupta et al. American Journal of Engineering Research, 2014, volume 3, issue 7, pages 33 to 43), may have properties such as water resistance, self-cleaning, and environmental resistance to chemical and biological degradation, and corrosion.

Therefore, there has been significant interest in the formation of artificial hydrophobic surfaces, which could provide the same useful and multifunctional properties as their natural counterparts.

Typically, artificial waterproof coatings are formed from a water repellent material dispersed with a volatile organic compound (VOC) solvent. Where the substrate is a porous material, such as concrete, the water repellent solution may also flow into the pores of the substrate. After removal of the solvent, the water repellent material remains on the surface of the substrate.

US 8,632,856 discloses a method of forming a water repellent material by use of a coating material comprising microparticles of a partially or fully fluorinated polymer and a binder of a partially fluorinated hexafluoropropylene copolymer, which are soluble in one or more of butyl acetate, ethyl acetate, methanol, dimethylacetaminde, dimethylformamide, dimethylsulfoxide, acetone, methyl ethyl ketone, sulfolane or tetrahydrofuran. The coating material is applied to at least a portion of a substrate, wherein the microparticles are added to the binder solution prior to applying to the substrate, or after applying of the binder solution to the substrate. The coated surface is subsequently heated so as to bond the microparticles to the binder, however, the heating temperature must be below that which would cause the water contact angle of the coating to fall below 80°. A further example is provided by WO 2018/122428, which discloses an ionogel-based omniophobic coating composition comprising an ionic liquid embedded in a crosslinked polymeric ionic liquid, which is linked to a modified substrate surface, and in which the ionic liquid and crosslinked polymeric ionic liquid are not covalently bonded. The ionic liquid is a compound of formula A_aB_b, wherein A is an organic cation comprising at least one omniophobic group and B is an anion comprising at least one charged atom selected from the group consisting of B-, P-, N-, C-, S-, O-, M- and combinations thereof. Coated materials are produced by: i) functionalising at least part of a surface of a substrate; ii) forming a mixture of a) an ionic crosslinking liquid, particularly of the formula SsQq-X-QqS, an organic solvent system (e.g. acetone, acetonitrile, tetrahydrofuran, dimethylsulfoxide, dimethylformamide and/or dichloromethane), an ionic liquid of formula A_aB_b, or a mixture thereof, and optionally, a monomeric ionic liquid, particularly of formula O_xB_b; iii) at least partially coating the functionalised substrate of step i) with the mixture prepared in step ii); iv) polymerising and crosslinking the coated surface of step iii); v) removing the solvent system used in step ii); and vi) coating the surface of the substrate obtained in step iii) with an ionic liquid as a lubricant, particularly an ionic liquid of formula A_aB_b.

Although water repellent coatings formed using volatile organic compounds result in materials demonstrating adequate water repellent performance, such methods are less desirable due to the required use of VOCs.

Volatile organic compounds are defined by the Environmental Protection Agency (EPA) as any compound of carbon, excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates and ammonium carbonate, which participates in atmospheric photochemical reactions, except those designated by the EPA as having negligible photochemical reactivity. In general, VOCs are any organic compounds having an initial boiling point less than or equal to 250 °C measured at a standard pressure of 101.3 kPa, and having fifteen or less carbon atoms. VOCs are considered to be damaging to both the environment (for example, causing tropospheric photochemical ozone formation, stratospheric ozone depletion, and the global greenhouse effect) and to human health (for example causing respiratory problems and damage to the liver, kidney and central nervous system, in addition some VOCs are suspected carcinogenics).

Accordingly, there is a need to provide effective water repellent compositions which are less toxic, as well as being more environmentally friendly.

Water-based water repellent compositions have been developed which have the advantage of minimising the organic solvents required. However, many of the conventional water-based compositions require the use of surfactants in order to help disperse the hydrophobic coating composition in water. Typical surfactants which may be used in water-based water repellent compositions include dimethlyhexynol, ethoxylated dinonyl phenol, an ethoxylated octylphenol, a branched ethoxylated alcohol, a linear ethoxylated alcohol, or a silicone surfactant. However, the surfactant can remain within the coatings formed, thereby reducing its water repelling effect. In addition, it has been found that many water-based water repellent materials are not suitably durable under working conditions.

Thus, there remains a need for a water repellent coating composition which is environmentally friendly and/or durable in use. In particular, there remains a need for a water repellent coating composition which can be formed using less toxic VOCs or in the absence of VOCs.

In addition, there remains a need for a cost effective artificial water repellent coating, which is preferably self-cleaning and resistant to chemical and biological degradation and/or corrosion. In particular, a water repellent coating which prevents or reduces the corrosive effect of aqueous based solvents on commonly used construction materials.

Further still, it would be of benefit to provide an alternative water repellent coating which can reduce the permeability of aqueous based solvents within porous construction materials, in order to reduce the occurrence of damp in buildings and infrastructure.

As discussed above, damp may occur in buildings which are not sufficiently impervious to water, resulting in the growth of mould on interior surfaces, causing adverse health effects to inhabitants. For example, inhaling mould fragments or spores can inflame the airways, causing nasal congestion, wheezing, chest tightness, coughing and throat irritation. Prolonged exposure to high levels of indoor dampness can reduce lung function and cause chronic health problems such as asthma. In addition, it is well known that pathogenic microbes can pose a significant threat to human health, and a variety of solutions have been developed to counter this threat. A particular area of concern is the microbial contamination of surfaces and the potential for the spread of disease and infection by contact with such contaminated surfaces. Effective methods are necessary to reduce microbial contamination of susceptible surfaces, for example in domestic and healthcare environments.

Typically, disinfecting measures kill fungi and/or bacteria that are present on surfaces at the time that they are applied, but tend to do so effectively only at the time of application. One reason for this is that the majority of disinfecting agents, once dried through evaporation, provide no protection against future infection of the surface. In addition, general cleaning, such as wiping a surface with a cloth, can remove many known disinfecting agents. Such surfaces can easily suffer recontamination, requiring frequent reapplication of the disinfectant. In some cases, is known to treat contaminated surfaces with disinfectant solutions containing relatively high concentrations in order to obtain broad spectrum disinfection. However, high concentrations of disinfectants are hazardous if brought into contact with food, and may also cause skin and eye irritation.

Thus, in addition to the properties discussed above, it would also be advantageous to produce a water repellent coating which, by keeping the surface dry, helps to provide an antimicrobial effect to alleviate or prevent the growth of fungi and/or bacteria on the surface of a substrate for extended periods of time, without requiring the use of toxic or hazardous chemicals or concentrations of chemicals which could considered to be toxic or hazardous.

Detailed Description of the Invention

The present invention is based at least in part on the surprising discovery that ionic liquid based coatings, wherein the ionic liquid is at least partially cross-linked, and additionally chemically bonded to a substrate, provide highly effective water repellent materials.

In a first embodiment, the present invention relates to a water repellent material, comprising a substrate and an ionic liquid based coating formed from an ionic liquid as shown in formula (i):

Formula (i) the ionic liquid being at least partially cross-linked, and additionally chemically bonded to the substrate, as shown in formula (ii) below:

Formula (ii) wherein, [X]⁺ is selected from nitrogen, sulphur or phosphorous;

R is a C₁ to C₁₂ alkyl group;

R¹ to R³ are each independently selected from a C₁ to C₁₈ straight chain or branched alkyl group, optionally substituted by one to three C₁ to C₁₆ straight chain or branched alkyl groups and/or one or more halogen groups; or R¹ to R³ are combined with [X]⁺ to form a heterocyclic group;

Y is divalent linking group selected from an aliphatic divalent linking group containing 1 to 10 carbon atoms or an aromatic divalent linking group; and

[Z]- is an anionic species.

The term “ionic liquid” as used herein refers to a liquid that is capable of being produced by melting a salt, and when so produced consists solely of ions. An ionic liquid may be formed from a homogeneous substance comprising one species of cation and one species of anion, or it can be composed of more than one species of cation and/or more than one species of anion. Thus, an ionic liquid may be composed of more than one species of cation and one species of anion. An ionic liquid may further be composed of one species of cation, and one or more species of anion. Still further, an ionic liquid may be composed of more than one species of cation and more than one species of anion. In a preferred embodiment, the ionic liquids of the present invention consist of one species of cation and one species of anion.

Ionic liquids generally exhibit a set of appealing physicochemical characteristics that typically include extremely low vapour pressure, large liquid range, non-degradability, non- flammability, good thermal stability and low toxicity. Together with the possibility of designing the properties of the ionic liquid by judicious choice of its constituent ions, together with the multiple combinations of ions that can result in low-melting salts, ionic liquids have been proposed for a broad range of applications.

In a preferred embodiment of the present invention, R may be selected from a C₁ to C₆ alkyl group. More preferably R is a methyl group or an ethyl group, and most preferably R is an ethyl group.

In one embodiment the crosslinking bond may be formed through a condensation reaction between OR groups of adjacent ionic liquid compounds. In a preferred embodiment, at least one OR group is a polymerisible group. It has been found that by at least partially crosslinking adjacent ionic liquids the mechanical properties of the water repellent coating can be improved. Accordingly, the durability of the resulting water repellent coating may be increased and the required time period before a further coating layer needs to be applied to the substrate surface is increased.

In addition, it is considered that at least partially crosslinking adjacent ionic liquids can improve the thermal stability of the coating layer. Accordingly, such water repellent materials would be suitable for use in, for example medical equipment, wherein such equipment is commonly heated to high temperatures before use for sterilisation purposes.

In some embodiments, the crosslinking bond between adjacent ionic liquids is formed using a crosslinking agent. The term “crosslinking agent" as used herein refers to an organic molecule having at least two polymerisable functional groups, which enable the formation of a three-dimensional network. In a particularly preferred embodiment, the crosslinking agent is selected a silicon alkoxide or an alkyl silicate, such as tetraethyl orthosilicate or tetramethyl orthosilicate.

Where the crosslinking agent is selected from tetraethyl orthosilicate or tetramethyl orthosilicate, it is possible for the non-bonding functional groups ( i.e . non-bonding methoxy or ethoxy groups) to be subsequently hydrolysed, thereby providing additional hydroxyl groups to which further ionic liquid groups may bond.

The person of skill in the art would be aware that the extent of crosslinking between adjacent ionic liquid compounds, once the ionic liquid dispersion is coated on the surface of a substrate, may be controlled by the amount of crosslinking agent present along with the temperature and pH of the dispersion. Accordingly, it would be within the common general knowledge of the skilled person to select an appropriate concentration of the crosslinking agent along with suitable reaction conditions in order to achieve the desired effect.

In some embodiments, at least one of R¹ to R³ is independently selected from a C₁ to C₁₈ straight chain or branched alkyl group, more preferably, a C₂ to C₁₄ straight chain or branched alkyl group, and most preferably a C₅ to C₈ straight chain or branched alkyl group. In some embodiments, at least one of R¹ to R³ is a methyl group.

In some embodiments, at least one of R¹ to R³ is independently selected from a C₁ to C₁₈ straight chain or branched alkyl group substituted with one or more halogen groups, preferably, a C₂ to C₁₄ straight chain or branched alkyl group substituted with one or more halogen groups, and most preferably a C₅ to C₈ straight chain or branched alkyl group substituted with one or more halogen groups. Preferably, the halogen group is selected from fluorine.

In an alternative embodiment, R¹ to R³ combine with [X]⁺ to form a heterocyclic group, wherein [X]⁺ is selected from nitrogen, sulphur or phosphorous. Preferably, [X]⁺ is nitrogen.

The heterocyclic group formed may be selected from pyridine, pyridazine, pyrimidine, pyrazine, pyrazole, imidazole, triazole, quinoline and isoquinoline. In a preferred embodiment, the heterocyclic group formed is selected from:

wherein: R^a, R^b, R^c, R^d, R^e, R^f, R^g, and R^h are each independently selected from hydrogen or a C₁ to C₁₈ straight chain or branched alkyl group, a C₁ to C₁₈ fluorinated alkyl group or a halogen. In preferred embodiments, one or more of R^a, R^b, R^c, R^d, R^e, R^f, R⁹, and R^h is selected from fluorine.

In some embodiments, Y is selected from a C₁ to C₁₀ straight chain or branched alkanediyl, substituted alkanediyl, dialkanylether or dialkanylketone, preferably Y is selected from C₁ to C₈ straight chain or branched groups as defined above, more preferably C₂ to C₅.

Preferably, Y is selected from -(CH₂-CH₂)-, (CH₂-CH₂-CH₂)-,-(CH₂-CH₂-CH₂-CH₂)-, -(CH₂- CH₂-CH₂-CH₂-CH₂)-, -(CH₂-CH₂-CH₂-CH₂-CH₂-CH₂)-, -(CH₂-CH₂-O-CH₂-CH₂)- and - (CH₂-CH₂-O-CH₂-CH₂-CH₂)-. Alternatively, Y may be selected from an aromatic hydrocarbon polymer, formed from polystyrene, parylene, polybutylene terephthalate, polycarbonate, polyether ketone, polysulfone, poly(1,4-phenylene), poly(1,4-phenylene-ethylene), poly(1,3-phenylene- methylene), and poly(p-phenylene vinylidene). Preferably, Y is selected from a functionalised styrene polymer such as para-vinyl toluene, α-methylstyrene, t-butyl styrene, and chlorostyrene polystyrene. More preferably, Y is a chloromethyl functionalised polystyrene (commonly referred to as Merrifield resin).

Merrifield Resin

The anion [Z]- may be selected from halides, pseudohalides, sulphates, sulfonates, phosphates, borates, carboxylates, nitrates, amides and/or imides.

By way of example, [Z]- may be: a) a halide anion selected from: F-, Cl-, Br-, l-; b) a sulphate anion selected from: [SO₄]^2-, [HSO₄]- and [R⁴SO₄]- c) a sulfonate anion selected from: [A¹SO₂O]-; d) a phosphate anion selected from: [H₂PO₄]-, [HPO₄]^2-, [PO₄]^3-, [A²OPO₃]^2-, [(A²O)₂PO₂]-; e) a carboxylate anion selected from: [A²CO₂]- or [HCO₂]-; f) a nitrate anion, [NO₃]-; g) a triflate anion, [CF₃SO₃]-; h) a silicate anion selected from: [SiO₃]^2-, [SiO₄]^4-; i) an amide anion selected from: [A¹ ₃N]^_; j) an imide anion selected from: [N(FSO₂)₂]-, and [N(Tf)₂]- and/or k) dianions or trianions, such as [CO₃]^2-, [C₂O₄]^2-, and [C₆H₅O₇]^3-. wherein: A¹ and A² are independently selected from the group consisting of C₁-C₁₆ alkyl, C₆ aryl, C₁-C₁₀ alkyl(C₆)aryl, and C₆ aryl(C₁-C₁₀)alkyl each of which may be substituted by one or more groups selected from: fluoro, chloro, bromo, iodo, C₁ to C₆ alkoxy, C₂ to C₁₂ alkoxyalkoxy, C₃ to C₆ cycloalkyl, C₆ to C₁₀ aryl, C₇ to C₁₀ alkaryl, C₇ to C₁₀ aralkyl, -CN, - OH, -SH, -NO₂, -CO₂R^x, -OC(O)R^x, -C(O)R^x, -C(S)R^x, -CS₂R^x, -SC(S)R^x, -S(O)( C₁ to C₆)alkyl, -S(O)O(C₁ to C₆)alkyl, -OS(O)(C₁ to C₆)alkyl, -S(C₁ to C₆)alkyl, -S-S(C₁ to C₆ alkyl), -NR^xC(O)NR^yR^z, -NR^xC(O)OR^y, -OC(O)NR^yR^z, -NR^xC(S)OR^y, -OC(S)NR^yR^z, - NR^xC(S)SR^y, -SC(S)NR^yR^z, -NR^xC(S)NR^yR^z, -C(O)NR^yR^z, -C(S)NR^yR^z, -NR^yR^z, or a heterocyclic group, wherein R^x, R^y and R^z are independently selected from hydrogen or C₁ to C₆ alkyl; and wherein: R⁴ is selected from a C₁ to C₁₆ straight chain or branched alkyl group.

In one preferred embodiment, [Z]- comprises a halide anion selected from: [F]-, [Cl]-, [Br]- , or [I]-.

In a further preferred embodiment, [Z]- comprises a sulphate anion selected from hydrogen sulphate (HSO₄-) or [(C₁ to C₁₂)SO₄)]-.

In a further embodiment, [Z]- comprises a sulfonate anion selected from trifluoromethanesulfonate [CF₃SO₃]- or [(C₁ to C₁₆)SO₃]-

In a further embodiment, [Z]- comprises an amide anion selected from dicyanamide [C₂N₃]-

In a further preferred embodiment, [Z]- comprises an imide anion selected from bis(fluorosulfonyl) imide [N(FSO₂)₂]-, and bis(trifluoromethylsulfonyl)imide ([N(Tf)₂]-).

In a further preferred embodiment, [Z]- comprises a carboxylate anion selected from [HCO₂]- or [A²CO₂]-, wherein A² is as defined above. Further examples of anions in this category include: [MeCO₂]-, [EtCO₂]-, [CH₂(OH)CO₂]-, [CH₃CH(OH)CH₂CO₂]-, 2-ethyl hexanoate ([CH₃(CH₂)₃CH(C₂H₅)CO₂]-), [(C₁ to C₁₆)CO₂]- and [PhCO₂]-.

In a further embodiment of the invention, [Z]- may comprise a fluorinated anion selected from: [BF₄]-, [CF₃BF₃]-, [CF₃CF₂BF₃]-, [PF₆]-, [CF₃PF5]-, [CF₃CF₂PF₅]-, [(CF₃CF₂)₂PF₄]-; and [(CF₃CF₂)₃PF₃]-. In a particularly preferred embodiment, [Z]- is selected from [F]-, [Cl]-, [Br]-, [I]-, [BF₄]-, [PF₆]- , 2-ethyl hexanoate ([CH₃(CH₂)₃CH(C₂H₅)CO₂]-), [(C₁ to C₁₆)CO₂]-, [(C₁ to C₁₆)SO₃], dicyanamide [C₂N₃]-, bis(fluorosulfonyl) imide [N(FSO₂)₂]-, trifluoromethanesulfonate [CF₃SO₃]- and bis(trifluoromethylsulfonyl)imide ([N(Tf)₂]-)- Suitable substrates include those to which an ionic liquid as defined above may be chemically bonded. For example, the substrate may be selected from glass, silica, metal, ceramic, mineral, plastic, polymer, fabric, fibre, wood, stone, clay, cement, natural hydraulic lime or concrete.

Preferably, the substrate may be selected from a construction material, such as brick, clay, mortar, concrete, metal, wood, magnesium oxide wallboard, render and tiles.

Alternatively, the substrate may be selected from a metal, such as gold, platinum, nickel, palladium, aluminium, chromium, copper, silver, lead, steel and galvanised steel. For example, the substrate may be a metal surface forming outer surface of a ship or motor vehicle, or a surface of a pipe.

The substrate may also be selected from a mineral, such as a hydrotalcite having the general formula [M²⁺ _1-XM³⁺ _x(OH)₂]^x+ (A^n-)_{x/n m}H₂O, wherein A- is selected from anions such as CO₃ ^2-, OH-, Cl-, or SO₄ ^2-.

Where the substrate is a natural or synthetic polymer, suitable polymers include rubber, phenolic resin, styrene-butidiene, polyisocyanurate, polyepoxides, polyester, for example polyethylene terephthalate, polybutylene terephthalate and others; polyvinyl chloride; polyvinylidene fluoride; polytetrafluoroethylene; polycarbonate; polyamide; aromatic polyamide; polyimide; poly(meth)acrylate; polystyrene; polyethylene; ethylene/vinyl acetate copolymer; polyurethane, and polycarbonate.

It will also be appreciated that, in principle, the substrate may be in the form of a medical device, equipment, or tubing, for example a glove, a mask, a garment, a bed sheet, a wound dressing, a prosthetic, an implant, a catheter, a syringe, a thermometer, forceps, retractors, scissors, a kidney dish, a scalpel or a surgical mesh.

In a further embodiment, wherein a water repellent and antimicrobial environment is required, such as in a healthcare environment, the substrate may be in the form of a wall, door, handle, railings, bed frame, furniture, cubical curtains or surgical drapes. It will be appreciated that substrates which comprise surface hydroxyl groups, which can form a chemical bond with cationic group of an ionic liquid as described above, are particularly preferred.

In a second aspect, there is provided a liquid dispersion for forming a water repellent surface, comprising a liquid medium and an ionic liquid as shown in formula (i) below:

Formula (i) wherein:

R may be selected from a C₁ to C₁₂ alkyl group or hydrogen ; and

[X]⁺, R₁ to R₃, Y, and [Z]- are as defined above.

In order to bond to the surface of the substrate, the ionic liquid of formula (i) must comprise at least one silanol group which is able to bond to a hydroxyl group present on the surface of the substrate, for example through a condensation reaction. In some embodiments, at least one OR group is a hydrolysable group such as an alkoxy group. Where at least one OR group comprises a hydrolysable group, the ionic liquid may be hydrolysed by any method known in the art either before or after the ionic liquid dispersion is added to the surface of a substrate in order to form the required silanol functionality.

Preferably, two R groups are selected from a C₁ to C₆ alkyl group, more preferably R is a methyl group or an ethyl group, most preferably R is an ethyl group.

The liquid medium may be selected from a polar or non-polar solvent. In particularly preferred embodiments, the liquid medium is selected from a polar solvent such as water, ethyl acetate or acetone, or an alcohol such as methanol, ethanol, propanol, isopropanol, or 2-butoxyethanol, or a combination thereof.

In a preferred embodiment, the liquid medium is selected from a solution of water, preferably distilled water, and an alcohol. In a particularly preferred embodiment, the liquid medium has a volume ratio of alcohol to water of between 70:30 and 99: 1 , more preferably the volume ratio of alcohol to water is 80:20 to 97:3, such as 95:5. Preferably, the alcohol is ethanol.

The ionic liquid may be at least partially soluble within the liquid medium, and in some embodiment may dissolve entirely within the liquid medium. In a particular embodiment, the ionic liquid and selected liquid medium may form an emulsion.

The concentration of ionic liquid in the liquid medium may be from 0.005 to 5.0 M, preferably from 0.01 to 1.0M, more preferably from 0.05 to 0.3M, and most preferably from 0.075 to 0.15 M.

The liquid dispersion may further comprise a crosslinking agent as defined above. In some embodiments, the molar ratio of crosslinking agent to ionic liquid is from 1 :0.5 to 1:25, preferably 1 :1 to 1:15, more preferably 1 :1 to 1:10.

In a third aspect, there is described a method of forming a water repellent material, comprising the steps of: i) providing an ionic liquid containing liquid dispersion as defined above; ii) providing a substrate, as defined above; iii) applying a coating layer of the ionic liquid containing liquid dispersion to at least a portion of the substrate; and iv) allowing the coating layer to at least partially cure; wherein the pH of the liquid dispersion is adjusted to a suitable pH such as to initiate crosslinking and enable bonding of the liquid dispersion to the substrate.

A coating layer of the ionic liquid containing liquid dispersion may be applied to the surface of the substrate using suitable known methods in the art. At least a portion of the substrate may be coated with the ionic liquid containing dispersion. Alternatively, the entire surface of the substrate may be contacted with the ionic liquid containing liquid dispersion.

In some embodiments, a single layer of the ionic liquid containing liquid dispersion may be applied to the substrate; thereafter the coating layer is at least partially cured. Preferably, the coating layer is fully cured. In an alternative embodiment of the present invention, multiple layers of the ionic liquid containing liquid dispersion are applied to the substrate, wherein the previous coating layer may be at least partially cured or fully cured before a subsequent coating layer is applied. It is considered that the application of multiple coating layers of the water repellent material enhances the overall durability of the coating layer. The corrosive effect of, for example acid rain, may, in time, remove an outer surface layer of the ionic liquid coating. However, where multiple coating layers are present, the required time period before a further coating layer needs to be applied to the substrate surface is increased.

The application of multiple layers of ionic liquid containing liquid dispersion onto the substrate surface allows the thickness of the coating layer, and therefore the durability of the coating layer, to be controlled depending on the specific use required.

In some embodiments, the thickness of the resulting water repellent material on the surface of the substrate is between 1 μm and 5 mm, preferably between 5 μm and 1 mm, more preferably between 10 μm and 0.1 mm.

The ionic liquid containing liquid dispersion may be applied to the surface of the substrate using standard processes known in this field, such as dipping, spin-coating, rolling, spraying and/or brushing.

In a preferred embodiment, the pH of the liquid dispersion is adjusted to less than or equal to 7.5, preferably the pH of the liquid dispersion is adjusted to less than 7, more preferably the pH of the liquid dispersion is adjusted to between 4 and 5. The pH of the liquid dispersion may be altered through the addition of an acid, preferably the acid is selected from acetic or formic acid. Under neutral conditions, the silanol functional groups of the ionic liquid react slowly with the substrate surface. However, it is noted that the reaction rate of hydrolysis (if required) and condensation increases under acidic conditions, for example when using an acid catalysts. The reaction rate of hydrolysis and condensation can increase by increasing the strength and/or concentration of the acid catalyst used.

The liquid dispersion may further comprise a catalyst in order to initiate crosslinking between RO-Si groups of adjacent ionic liquid groups. Preferably, the catalyst is a transition metal catalyst, for example containing tin. Suitable catalysts include organotin catalysts, such as dibutyltin dilaurate. Alternatively, the catalyst may be added after a coating of the ionic liquid containing liquid dispersion has been applied to the substrate material.

Before coating the surface of the substrate with a layer of the ionic liquid containing liquid dispersion, the liquid dispersion may be first mixed or agitated for between 30 seconds and 24 hours before the solution is applied to the substrate, to ensure a homogeneous dispersion of the ionic liquid, crosslinking agent, and optionally the catalyst. Mixing or agitating may be performed by any known method in the art.

The method may further comprise the step of removing surface impurities from the substrate before coating the substrate with the ionic liquid containing liquid dispersion. The removal of non-bonding contaminants, such as sodium, potassium and calcium, from the surface of the substrate can increase the number of ionic liquids which may bond to the surface of the substrate and improve the stability of the bonds formed. Surface impurities may be reduced, for example, by immersion of the substrate in 5% hydrochloric acid for 4 hours, and subsequently washing the substrate with deionized water. The substrate may then be immersed in deionized water overnight followed by drying. Alternatively, oxides with high isoelectric points can adsorb carbon dioxide, forming carbonates. The carbonates formed can be removed from the substrate using a high temperature vacuum bake.

In some embodiments, the method further comprises the step of pre-treating the substrate before coating the substrate with the ionic liquid containing liquid dispersion, so as to increase the number of surface hydroxyl groups present. The pre-treating step therefore increases the number of reactive sites on the surface of the substrate to which the above mentioned ionic liquids may bond. Preferably, the pre-treatment consists of contacting the substrate with an acid or base bath. More preferably, the pre-treatment consists of contacting the substrate with a base bath comprising a sodium hydroxide solution.

By way of example, where the substrate is glass, the pre-treatment step may comprise contacting the substrate with 10-20% HCI in deionised water at approximately 25 °C for 24 hours. Alternatively, the pre-treatment step may comprise contacting a glass substrate with a piranha solution (3 parts concentrated H₂SO₄ to 1 part 30% H₂O₂) at 100 °C for 10 min. Other methods of increasing the surface hydroxyl groups of a glass substrate will be well known to the skilled person.

By way of further example, where the substrate is masonry, the pre-treatment step may comprise contacting the substrate with a 10-20 % sodium hypochlorite solution at a temperature from 5 to 30°C. Following the step of contacting the substrate with the sodium hypochlorite solution the substrate is allowed to dry for approximately one hour. Alternatively, the pre-treatment step may comprise contacting the masonry substrate with a quaternary ammonium salt solution, preferably an anti-bacterial quaternary ammonium salt solution, such as tetramethylammonium hydroxide and tetrabutylammonium hydroxide at a temperature of from 5 to 30°C. Following the step of contacting the substrate with the quaternary ammonium salt the substrate is allowed to dry for approximately one hour. Following the step of coating of the ionic liquid containing liquid dispersion on the surface of the substrate, the ionic liquid coating layer is at least partially cured, thereby forming a covalent bond with substrate with concomitant loss of water.

In some embodiments, the ionic liquid coating may be allowed to cure at room temperature (approximately 25°C), wherein the curing time may be between 1 minute and 7 days, preferably between 10 minutes and 5 days, more preferably between 1 hour and 2 days. The person of skill in the art would be aware that in embodiments wherein the pH of the liquid dispersion is reduced, the required curing time may also be reduced.

In some embodiments, heat may be applied in order to reduce the curing time of the coating layer, for example the substrate coated with the ionic liquid containing liquid dispersion may be heated to a temperature of between 25 and 150 °C, preferably between 50 and 100 °C, more preferably between 75 and 90 °C.

Alternatively, the ionic liquid containing liquid dispersion coating layer may be cured using an ultrasound treatment.

Preferably, before or during the curing step the ionic liquid coated substrate is dried so as to remove the liquid medium through evaporation. Preferably, at least 50% by volume of the liquid medium is evaporated from the ionic liquid containing liquid dispersion coating layer, preferably at least 60% by volume, more preferably at least 75% by volume, still more preferably at least 85% by volume, most preferably at least 95% by volume.

As a further alternative, the ionic liquid containing liquid dispersion coating layer may be cured by controlling the pH of the coating layer, for example an acid, such as acetic acid or formic acid may be added to the coating composition in order to reduce the curing time as discussed above. Preferably, any remaining water and/or acid following hydrolysis and/or the curing step is at least substantially removed through evaporation. Preferably, at least 50% by volume of the water and/or acid is evaporated from the water repellent coating, preferably at least 60% by volume, more preferably at least 75% by volume, still more preferably at least 85% by volume, most preferably at least 95% by volume.

According to a fourth aspect, there is described the use of an ionic liquid as an additive for forming a water repellent surface, wherein the ionic liquid is at least partially crosslinked, and additionally chemically bonded to a substrate via the cationic group, the ionic liquid being selected from formula (i):

Formula (i) wherein R may be selected from a C₁ to C₁₂ alkyl group or hydrogen, as defined above; and

R¹, R², R³, [X]⁺, and Y are as defined above.

Preferably, the ionic liquid may be in the form of a dry powder or a liquid.

In some embodiments, the ionic liquid additive may further comprise a liquid medium so as to form a liquid coating composition, for example the liquid coating composition may be a paint composition.

In some embodiments, the ionic liquid may be chemically bonded to a support in particulate or powder form so as to form a supported ionic liquid. These supported ionic liquids may then be used to form a coating composition for forming a water repellent surface. For example, the supported ionic liquid (particles/powder) may be incorporated into a rendering formulation which would then be applied to a substrate and cured. Suitable support materials include glass, silica, metal, ceramic, mineral, plastic, polymer, fabric, fibre, wood, stone, clay, cement, natural hydraulic lime or concrete.

Alternatively, the support may be selected from a metal, such as gold, platinum, nickel, palladium, aluminium, chromium, copper, silver, lead, steel and galvanised steel.

As a further alternative, the support material may be selected from a mineral, such as a hydrotalcite having the general formula [M²⁺ _1-xM³⁺ _x(OH)₂]^x+ (A^n-)_{x/n m}H₂O, wherein A- is selected from anions such as CO₃ ^2-, OH-, Cl-, or SO₄ ²

Where the support is a natural or synthetic polymer, suitable polymers include rubber, phenolic resin, styrene-butidiene, polyisocyanurate, polyepoxides, polyester, for example polyethylene terephthalate, polybutylene terephthalate and others; polyvinyl chloride; polyvinylidene fluoride; polytetrafluoroethylene; polycarbonate; polyamide; aromatic polyamide; polyimide; poly(meth)acrylate; polystyrene; polyethylene; ethylene/vinyl acetate copolymer; polyurethane, and polycarbonate.

In embodiments where the ionic liquid additive or coating composition is in the form of a solid material, the additive or coating composition may further comprise a liquid medium to form of a wet paste composition.

Where the additive is in the form of a liquid coating composition or paste, the composition preferably comprises a polar or non-polar solvent. In a preferred embodiment the composition comprises a polar solvent such as water, ethyl acetate, acetone or an alcohol, such as methanol, ethanol, propanol, isopropanol, or 2-butoxyethanol, or a combination thereof.

The concentration of the above disclosed ionic liquid in the liquid coating composition may be between 0.005 and 5.0 M, preferably between 0.05 and 0.3M, more preferably between 0.075 and 0.15 M.

The liquid coating composition or wet paste may further comprise a crosslinking agent. The crosslinking agent may be selected from a silicon alkoxide or an alkyl silicate, such as tetraethyl orthosilicate ortetramethyl orthosilicate. In preferred embodiments, the molar ratio of crosslinking agent to ionic liquid is from 1 :0.5 to 1:25, preferably 1 :1 to 1:15, more preferably 1 :1 to 1:10.

In a fifth aspect, the present invention relates to the use of an ionic liquid based coating as defined above as a water repellent coating.

In a sixth aspect, the present invention relates to the use of an ionic liquid based coating as defined above as an antimicrobial coating, in addition to its water repellent properties.

The antimicrobial activity of certain ionic liquids was originally reported by Pernak et al. (Przemysl Chemiczny, 2000, 79, 150-153; Green Chemistry, 2003, 5, 52-56). After several studies investigating clinically relevant pathogens in planktonic mode, it has also been found that ionic liquids can fight pathogens in the form of biofilms (Carson et al., Green Chemistry, 2009, 11, 492-497). The biological activity of an ionic liquid is dependent on the ionic liquid structure, along with the physical and chemical characteristics of the ionic liquid. For example, it has been demonstrated that longer alkyl chain lengths provide increased ionic liquid cytotoxicity (Ecotoxicology and Environmental Safety 83 (2012) 102-107). The most suitable ionic liquid for a particular application is therefore highly dependent on the structure of ionic liquid (Hough et al., New Journal of Chemistry, 2007, 31 , 1429-1436). The use of antimicrobial ionic liquids in the formation of antimicrobial surface-coating films has been disclosed in WO 2009/125222.

As used herein, the term antimicrobial refers to the ability of an ionic liquid to treat or control (e.g. reduce, prevent, inhibit, break down, or eliminate) microbial growth or survival at any concentration.

In particular, the above-mentioned ionic liquids may show efficient antimicrobial activity against a variety of Gram-positive bacteria, including methicillin resistant Staphylococcus aureus , methicillin sensitive Staphylococcus aureus , Staphylococcus epidermidis , and Enterococcus faecalis. In some cases, antimicrobial activity is also observed from some Gram-negative bacteria, including Pseudomonas aeruginosa , Burkholderia cepacia complex, Klebsiella aerogenes, and Proteus mirabilis. The ionic liquid may also retard the formation of biofilms in some cases.

In a seventh aspect, the present invention relates to the use of an ionic liquid based coating as defined above as an anti-static coating.

Aspects of the present inventions will now be described by way of example, with reference to the accompanying Figures, in which:

Figure 1 shows a water droplet on the surface of a render comprising no extra coating (left); a commercial fluoropolymer coating which was subsequently oven cured for 30 minutes (middle), and a coating in accordance with the present invention (right).

Examples

Method of forming a water repellent material

Example 1 - Method of forming water repellent materials according to the present invention through an ionic liquid tethering process

Acetic acid was added to a 95%/5% by volume ethanol: distilled water solution until the pH of the solution was adjusted to pH 4.5. An ionic liquid, as defined below, was then added to the acidified solution to form a 0.1 M ionic liquid solution. The ionic liquid solution was subsequently stirred for 5 minutes so as to ensure a uniform dispersion of the ionic liquid within acidified solution. A surface coating of the ionic liquid solution was then applied to a substrate surface.

Example 2 Method of forming water repellent materials according to the present invention through the formation of ionogels

An ionic liquid solution was formed containing tetramethoxysilane (TMOS), formic acid (FA) along with an ionic liquid as defined below, wherein the molar ratio of TMOS, FA, and the ionic liquid within the solution was 1.0 : 7.8 : 0.5, respectively. A surface coating of the ionic liquid solution was then applied to the surface of a substrate, which was subsequently allowed to cure for 24 hours at room temperature.

Analysis of the water resistance of the water repellent materials formed

Fifteen water repellent materials were formed according to Example 1 , wherein the ionic liquids used to form the water repellent coatings are shown in the Table 1 below:

Table 1

The effectiveness of the water-repellent coatings was assessed based on the contact angle of water on the materials formed. Methods of measuring the contact angle of a water droplet on the surface of a substrate are well known to the skilled person, for example through the use of the ISO standard, ISO 19403-1:2017. For comparison, the contact angle of the substrate without a water repellent coating and a substrate simply coated with tetraethyl orthosilicate (TEOS) were also measured. The ionic liquid coating layer was allowed to cure for 24 hours at room temperature before measuring the contact angle of water on the sample surface, unless otherwise stated. The results of the analysis are illustrated in Table 2. Table 2

Table 2 clearly illustrates a significant increase in the contact angle of water on the ionic liquid coated substrate compared to the substrate coated with TEOS (control), signifying an improved water repellent effect on the ionic liquid coated substrates. In particular, the contact angle of Scraped K1 -sandstone is 60.82°, however when this substrate is coated with Si modified didecylmethylammonium chloride ([NMe(dec)₂]CI Si mod), the contact angle of water is significantly increased to 121.42°. Similarly, the contact angle of smooth K1-white (render) is 50.19°, however, when this substrate is coated with Si modified didecylmethylammonium chloride ([NMe(dec)₂]CI Si mod), the contact angle is increased to 75.12°.

The water repellent effect of the above ionic liquid coatings is shown in Figure 1 , which illustrates a water droplet on the surface of a render, wherein the left-hand image illustrates the control render with no extra coating, the middle image illustrates a commercial fluoropolymer coating for render, which was subsequently oven cured for 30 minutes, and the right-hand image illustrates a coating formulation containing [P₈₈₈]CI Si mod, produced following Example 1 above and using a 30 minute oven cure. After 30 seconds the image was captured showing that the control had wetted considerably. In contrast, the [P₈₈₈]CI Si mod coating portion caused the water droplet to bead and the effect was similar to the commercial fluoropolymer coating.

CIELAB colour space is used to give quantifiable numbers to the colour of an object or material. Three values are recorded L* (lightness) from black (0) to white (100), a* from green (-) to red and b* from blue (-) to yellow (+). ΔE is used to calculate the change in colour from two sets of L*a*b* measurements with a smaller ΔE value indicating a smaller change in colour between the two samples. This technique is useful in quantifying the effect weathering has on the change in colour of painted surfaces.

In order to assess the water repellent effect of the above ionic liquid based coating layers, CIELAB colour space analysis of two samples were reviewed, wherein the first sample consisted of a cementitious render panel painted with a commercial resin paint and a second sample consisted of a cementitious render panel painted with a silicon resin paint containing 0.35% [P₈₈₈]CI Si mod additive. The render panels were painted (2 coats) with the chosen paint and allowed to dry at room temperature for 7 days. L*A*B* values were recorded initially after the paint had cured indoors, to determine the colour properties of the painted panels. The panels were then subjected to 500 hours of continuous cycling of water spray, condensation formation (40 °C) and UV light exposure (50 °C) using a QUV accelerated weathering tester to recreate the conditions of outdoor weathering on the samples. Upon removal of the samples from the QUV weathering apparatus L*A*B* values were once more collected for the panels and a ΔE value was determined comparing the samples pre and post weathering.

The results of this analysis are shown in Table 3.

Table 3:

The silicon resin paint with [P₈₈₈]CI Si mod additive had a ΔE = 0.6 versus a ΔE = 1.1 for the commercial silicon resin paint, suggesting that the addition of the ionic liquid coating layer improved the durability of the coating.

Claims

1. A water repellent material, comprising a substrate and an ionic liquid based coating formed from an ionic liquid as shown in formula (i):

Formula (ii) wherein, [X]⁺ is selected from nitrogen, sulphur or phosphorous;

R is a C₁ to C₁₂ alkyl group;

R¹ to R³ are each independently selected from a C₁ to C₁₈ straight chain or branched alkyl group, optionally substituted by one to three C₁ to C₁₆ straight chain or branched alkyl groups and/or one or more halogen groups; or R¹ to R³ are combined with [X]⁺ to form a heterocyclic group; Y is divalent linking group selected from a aliphatic divalent linking group containing 1 to 10 carbon atoms or an aromatic divalent linking group; and [Z]- is an anion.

2. A water repellent material according to claim 1 , wherein R is selected from a C₁ to C₆ alkyl group, preferably R is a methyl or an ethyl group.

3. A water repellent material according to claim 1 or claim 2, wherein the crosslinking bond is formed through a condensation reaction between OR groups of adjacent ionic liquid compounds.

4. A water repellent material according to claim 1 or 2, wherein the crosslinking bond is formed using a crosslinking agent, preferably the crosslinking agent is selected from a silicon alkoxide or an alkyl silicate, more preferably the crosslinking agent selected from tetraethyl orthosilicate or tetramethyl orthosilicate.

5. A water repellent material according to any preceding claim, wherein at least one of R¹ to R³ is independently selected from a C₁ to C₁₈ straight chain or branched alkyl group, preferably a C₂ to C₁₄ straight chain or branched alkyl group, more preferably at least one of R¹ to R³ is a methyl group.

6. A water repellent material according to any one of claims 1 to 4, wherein at least one of R¹ to R³ is independently selected from a C₁ to C₁₈ straight chain or branched alkyl group substituted with one or more halogen groups, preferably, a C₂ to C₁₄ straight chain or branched alkyl group substituted with one or more halogen groups, and wherein the halogen group is preferably selected from fluorine.

7. A water repellent material according to any one of claims 1 to 4, wherein R¹ to R³ are combined with [X]⁺ to form a heterocyclic group, preferably [X]⁺ is nitrogen.

8. A water repellent material according to claim 7, wherein the heterocyclic group is selected from pyridine, pyridazine, pyrimidine, pyrazine, pyrazole, imidazole, triazole, quinoline and isoquinoline, preferably the heterocyclic group is selected from:

wherein: R^a, R^b, R^c, R^d, R^e, R^f, R^g, and R^h are each independently selected from hydrogen or a C₁ to C₁₈ straight chain or branched alkyl group, a C₁ to C₁₈ fluorinated alkyl group, or a halogen.

9. A water repellent material according to any preceding claim, wherein Y is selected from a C₁ to C₁₀ straight chain or branched alkanediyl, substituted alkanediyl, dialkanylether or dialkanylketone, preferably a C₁ to C₈ straight chain or branched alkanediyl, substituted alkanediyl, dialkanylether or dialkanylketone, more preferably a C₂ to C₅ straight chain or branched alkanediyl, substituted alkanediyl, dialkanylether or dialkanylketone_.

10. A water repellent material according to claim 9, wherein Y is selected from -(CH₂-CH₂)- , (CH₂-CH₂-CH₂)-,-(CH₂-CH₂-CH₂-CH₂)-, -(CH₂-CH₂-CH₂-CH₂-CH₂)-, -(CH₂-CH₂-CH₂- CH₂-CH₂-CH₂)-, -(CH₂-CH₂-O-CH₂-CH₂)- and -(CH₂-CH₂-O-CH₂-CH₂-CH₂)-.

11. A water repellent material according to any one of claims 1 to 8, wherein Y is selected from an aromatic hydrocarbon polymer, preferably Y is selected from polystyrene, parylene, polybutylene terephthalate, polycarbonate, polyether ketone, polysulfone, poly(1,4-phenylene), poly(1,4-phenylene-ethylene), poly(1,3-phenylene-methylene), and poly(p-phenylene vinylidene).

12. A water repellent material according to claim 11, wherein Y is selected from a functionalised styrene polymer, such as para-vinyl toluene, α-methylstyrene, t-butyl styrene, and chlorostyrene polystyrene, preferably Y is a choromethyl functionalised polystyrene (Merrifield resin).

13. A water repellent material according to any preceding claim, wherein [Z]- is an anion selected from the group comprising halides, pseudohalides, phosphates, sulphates, sulfonates, borates, carboxylates, amides, and imides.

14. A water repellent material according to claim 13, wherein [Z]- is selected from [F]-, [Cl]- , [Br]-, [I]-, [BF₄]-, [PFe]-, 2-ethyl hexanoate ([CH₃(CH₂)₃CH(C₂H₅)CO₂]-), [(C₁ to C₁₆)CO₂]^·, hydrogen sulphate (HSO₄- ), [(C₁ to C₁₂)SO₄)]-, [(C₁ to C₁₆)SO₃]-, dicyanamide [C₂N₃]-, bis(fluorosulfonyl) imide [N(FSO₂)₂]-, trifluoromethanesulfonate [CF₃SO₃]- and bis(trifluoromethylsulfonyl)imide ([N(Tf)₂]-).

15. A water repellent material according to any preceding claim, wherein the substrate is selected from the group comprising glass, silica, metal, ceramic, mineral, plastic, fabric, fibre, wood, stone, clay, cement, natural hydraulic lime, concrete and polymer materials.

16. A water repellent material according to claim 15, wherein the substrate comprises surface hydroxyl groups.

17. A water repellent material according to any one of claims 1 to 16, wherein the substrate is a construction material or a medical device.

18. A liquid dispersion for forming a water repellent coating, comprising a liquid medium and an ionic liquid as shown in formula (i) below:

Formula (i) wherein R is selected from a C₁ to C₁₂ alkyl group or hydrogen; and R¹, R², R³, [X]⁺, Y and [Z]-, are as defined in claims 1 to 14.

19. A liquid dispersion according to claim 18, wherein at least one OR group is selected from hydrolysable group, such as an alkoxy group.

20. A liquid dispersion according to claim 18 or 19, wherein the liquid medium is selected from a polar solvent, such as water, ethyl acetate or acetone, or an alcohol, such as methanol, ethanol, propanol, isopropanol, or 2-butoxyethanol, or a combination thereof.

21. A liquid dispersion according to claim 20, wherein the liquid medium is an alcohol/distilled water solution, preferably the liquid medium has a volume ratio of alcohol to water of between 70:30 and 99:1 , more preferably the liquid medium comprises a 95:5 volume ratio of alcohol/distilled water.

22. A liquid dispersion according to any one of claims 18 to 21 , wherein the concentration of the ionic liquid in the liquid medium is from 0.005 to 5.0 M, preferably from 0.01 to 1.0M, more preferably from 0.05 to 0.3M, most preferably from 0.075 to 0.15 M.

23. A liquid dispersion according to any one of claims 18 to 20, wherein the liquid dispersion further comprises a crosslinking agent, preferably a crosslinking agent as defined in claim 6.

24. A liquid dispersion according to claim 23, wherein the molar ratio of the crosslinking agent to ionic liquid is from 1 :0.5 to 1 :25, preferably from 1 :1 to 1:15, more preferably from 1:1 to 1 :10.

25. A method of forming a water repellent material, comprising the steps of: i) providing an ionic liquid containing liquid dispersion as defined in any one of claims 18 to 24; ii) providing a substrate as defined in any one of claims 15 to 17; iii) applying a coating layer of the ionic liquid containing liquid dispersion to at least a portion of the substrate; and iv) allowing the coating layer to at least partially cure; wherein the pH of the liquid dispersion is adjusted to a suitable pH such as to initiate cross-linking and enable bonding of the liquid dispersion to the substrate.

26. A method according to claim 25, wherein a coating layer of the ionic liquid containing liquid dispersion is applied to at least an entire surface of the substrate.

27. A method according to Claim 25 or 26, wherein multiple layers of the ionic liquid containing liquid dispersion are applied to the substrate and wherein the previous layer is partially or fully cured before a subsequently layer is applied to the substrate.

28. A method according to any one of claims 25 to 27, wherein the ionic liquid containing liquid dispersion is applied to at least a portion of the substrate by dipping, spin-coating, rolling, spraying or brushing.

29. A method according to any one of claims 25 to 28, wherein the thickness of the water repellent material on the surface of the substrate is between 1 μm and 5 mm, preferably between 5μm and 1 mm, more preferably between 10 μm and 0.1 mm.

30. A method according to any one of claims 25 to 29, wherein the ionic liquid containing liquid dispersion further comprises a crosslinking agent, preferably a crosslinking agent as defined in claim 6.

31. A method according to any one of claims 25 to 30, wherein the ionic liquid containing liquid dispersion further comprises a catalyst to initiate crosslinking between RO-Si groups of adjacent ionic liquid compounds.

32. A method according to any one of claims 25 to 31 , further comprising the step of adding a catalyst to the ionic liquid containing liquid dispersion after a coating of the ionic liquid containing liquid dispersion has been applied to the substrate, to initiate crosslinking between RO-Si groups of adjacent ionic liquid compounds.

33. A method according to claim 31 or 32, wherein the catalyst is a transition metal catalyst, for example a transition metal catalyst containing tin, preferably the catalyst is an organotin catalyst, more preferably the catalyst is dibutyltin dilaurate.

34. A method according to any one of claims 25 to 33, wherein the liquid dispersion comprises a liquid medium selected as defined in claim 20 or 21.

35. A method according to claim 34, wherein the concentration of the ionic liquid in the liquid dispersion is from 0.005 to 5.0 M, preferably from 0.01 to 1.0M, more preferably from 0.05 to 0.3M, most preferably from 0.075 to 0.15 M.

36. A method according to anyone of claims 25 to 35, wherein the pH of the liquid dispersion is adjusted through the addition of an acid, preferably acetic or formic acid.

37. A method according to any one of claims 25 to 36, wherein the pH of the solution is adjusted to less than or equal to 7.5, preferably less than 7, more preferably between 4 and 5.

38. A method according to any one of claims 25 to 37, wherein the liquid dispersion is mixed or agitated for between 30 seconds and 24 hours before the solution is applied to the substrate, preferably the liquid dispersion is mixed or agitated for between 30 seconds and 1 hour before the solution is applied to the substrate, preferably between 1 minute and 30 minutes, more preferably between 3 minutes and 10 minutes.

39. A method according to any one of claims 25 to 38, wherein the method further comprises the step of removing surface impurities from the substrate before applying the coating layer of the ionic liquid containing liquid dispersion.

40. A method according to claim 39, wherein the step of removing surface impurities from the substrate comprises immersing the substrate in an acid solution, such as a 5% hydrochloric acid solution or the step of removing surface impurities from the substrate comprises contacting the substrate with one or more oxide having a high isoelectric point.

41. A method according to any one of claims 25 to 40, wherein the method further comprises the step of pre-treating the substrate to increase the amount of surface hydroxyl groups, preferably the pre-treatment comprises contacting the substrate with an acid or base bath.

42. A method according to Claim 41 , wherein the pre-treatment comprises contacting the substrate with a base bath comprising a sodium hydroxide solution.

43. A method according to any one of claims 25 to 42, wherein the coating layer of ionic liquid containing liquid dispersion is cured at room temperature.

44. A method according to any one of claims 25 to 42, wherein the coating layer is cured at a temperature of between 25 and 150 °C, preferably between 50 and 100 °C, more preferably between 75 and 90 °C.

45. A method according to any one of claims 25 to 42, wherein the coating layer is cured by using an ultrasound treatment.

46. A method according to any one of claims 25 to 42, wherein the curing reaction is initiated by adding water to the coating layer to hydrolyse any hydrolysable groups present or by reducing the pH of the coating layer by adding an acid.

47. Use of an ionic liquid as an additive for forming a water repellent surface, wherein the ionic liquid is at least partially cross-linked, and additionally chemically bonded to a substrate via the cationic group, the ionic liquid being selected from formula (i):

Formula (i) wherein R is selected from a C₁ to C₁₂ alkyl group or hydrogen; and R¹, R², R³, [X]⁺, and Y, are as defined in claim 1 to 19.

48. Use of an ionic liquid according to Claim 47, wherein the ionic liquid is in the form of a dry powder.

49. Use of an ionic liquid according to claim 47, wherein the ionic liquid further comprises a liquid medium so as to form a liquid coating composition, preferably the coating composition is a paint composition.

50. Use of an ionic liquid according to claim 48, wherein the ionic liquid is chemically bonded to a support in particulate or powder form forming a supported ionic liquid.

51. Use of an ionic liquid according to Claim 50, wherein the support is selected from a material as defined in Claim 15 or 16.

52. Use of an ionic liquid according to claim 48, wherein the coating composition further comprises a liquid medium so as to form a wet paste composition.

53. Use of an ionic liquid based coating according to claim 1 as a water repellent coating.

54. Use of an ionic liquid based coating according to claim 53, wherein the water repellent coating is an antimicrobial coating.

55. Use of an ionic liquid based coating according to claim 53, wherein the water repellent coating is an anti-static coating.