Temperature stable hydrophilic and superhydrophilic coatings

Abstract

The present invention relates to a composition comprising (i) an aminosilane or a hydrolysed aminosilane, (ii) silica, and (iii) water; wherein the weight ratio of (i) aminosilane or hydrolysed aminosilane to (ii) silica is from about 1:1.5 to about 1:12; and wherein the weight 5 ratio of (i) aminosilane to (iii) water is at least about 1:3. Also provided is a hydrophilic or superhydrophilic coating formed from the compositions of the invention.

Description

[0001] Temperature stable hydrophilic and superhydrophilic coatings

[0002] Field of the invention

[0003] The present invention relates to temperature stable hydrophilic and superhydrophilic coatings. These may be useful for coating electric overhead conductors, and can reduce corona noise or discharge.

[0004] Background

[0005] Superhydrophilicity is defined as the extreme hydrophilic behaviour of a material or surface, characterized by a water contact angle (0) close to zero degrees. It is generally accepted that the first prerequisite for a surface to be superhydrophilic (superwetting) is that its apparent contact angle with water is less than 10°. The water contact angle is a measure of the wetting behaviour of a liquid on a solid surface. For superhydrophilic surfaces, the contact angle is so small that water spreads out uniformly across the surface, forming a thin and continuous film.

[0006] Superhydrophilic coatings can be used in various applications, including for example in selfcleaning coatings, antifogging coatings, antifouling coatings and heat exchangers.

[0007] Known superhydrophilic coatings have been found to be unsuitable for use at high temperatures. It would therefore be desired to create hydrophilic and superhydrophilic coatings that are stable at temperatures higher than ambient, e.g. up to about 100°C.

[0008] Summary

[0009] According to an aspect of the present invention there is provided a composition comprising (i) an aminosilane or a hydrolysed aminosilane, (ii) silica, and (iii) water; wherein the weight ratio of (i) aminosilane or hydrolysed aminosilane to (ii) silica is from about 1 :1.5 to about 1 : 12; and wherein the weight ratio of (i) aminosilane to (iii) water is at least about 1 :3.

[0010] In one aspect the composition is a composition for coating an overhead conductor.

[0011] The invention also provides a hydrophilic or superhydrophilic coating formed from the compositions described herein. Also provided herein is a hydrophilic or superhydrophilic coating comprising (i) aminomodified silica and (ii) silica; wherein the weight ratio of (i) amino-modified silica to (ii) silica is from about 1:1.5 to about 1:12.

[0012] In one aspect the invention provides a substrate comprising the coating described herein, and / or a substrate which has been treated with the composition described herein. In embodiments the substrate is an overhead conductor.

[0013] In one aspect the invention provides a method of forming a hydrophilic or superhydrophilic coating, or a method of coating a substrate, the method comprising applying the composition described herein to a substrate (e.g. an overhead conductor). The method may further comprise curing the composition.

[0014] In one aspect the invention provides the use of the coating composition and / or coated described herein, to reduce corona noise from an overhead conductor.

[0015] In one aspect the invention provides a method for reducing corona noise from an overhead conductor, the method comprising applying the composition described herein to the overhead conductor, and optionally allowing the composition to cure.

[0016] Detailed Description

[0017] Disclosed herein is a composition comprising (i) an aminosilane, (ii) silica, and (iii); wherein the dry weight ratio of (i) aminosilane to (ii) silica is from about 1:1.5 to about 1:12; and wherein the weight ratio of (i) aminosilane to (iii) water is at least about 1 :3.

[0018] The compositions described herein may be used to form a hydrophilic or superhydrophilic coating on a substrate (such as an overhead conductor), and / or to reduce corona noise from an overhead conductor.

[0019] Importantly, it has been found that the coatings formed by the compositions described herein are both hydrophilic or superhydrophilic (preferably superhydrophilic), and are stable at elevated temperatures. This means that the coatings retain their hydrophilic or superhydrophilic properties even when heated, e.g. to about 100°C. Such temperature stability can be critical in certain uses, for example for coatings applied to substrates which are exposed to elevated temperatures, such as overhead conductors and power lines. The coatings described herein have also been found to have a high abrasion resistance and are optically clear. The coating compositions can also be easily applied (e.g. with facile application methods such as a brush, spray or wipe), can be applied in a single layer, and undergo rapid curing at ambient temperatures. Accordingly, the coatings and compositions described herein are suitable for a wide range of industrial applications as outlined in this specification.

[0020] It has also been found that the coatings can mitigate the corona effect, which occurs when the electric field around a high-voltage conductor ionizes the surrounding air, creating a visible bluish glow. The corona effect can cause a range of undesirable effects such as power loss, audible noise, electromagnetic interference, ozone production and light emissions. By reducing the contact angle between the overhead conductor and water, the corona effect can be reduced. Thus, the compositions and hydrophilic and superhydrophilic coatings of the present invention are useful in reducing the corona effect.

[0021] Aminosilane

[0022] The compositions described herein comprise an aminosilane, which is a type of organosilicon compound that contains both amino groups and silane groups.

[0023] In embodiments the aminosilane is a primary, secondary or tertiary aminosilane (i.e. the amino functional group is a primary or secondary amine). In embodiments the aminosilane is a primary or secondary aminosilane. In embodiments the aminosilane is a primary aminosilane.

[0024] In embodiments the aminosilane comprises a single amino functional group. In other embodiments the aminosilane comprises two or more (e.g. two) amino functional groups. In embodiments the aminosilane is a diaminosilane.

[0025] The aminosilane used herein may have the formula Si(OR)a(R)b(X)c, wherein R is any suitable organic group, X contains an amino group, a is from 1 to 3, b is from 0 to 2, and c is from 1 to 3, with the proviso that a+b+c =4.

[0026] Preferably a is 2 or 3, and more preferably a is 3. Preferably b is 0 or 1 , and more preferably b is 0.

[0027] Preferably c is 1 or 2, and more preferably c is 1.

[0028] Preferably R is H or an alkyl group such as a Ci-e alkyl, and more preferably R is selected from H, methyl, ethyl or propyl, such as ethyl.

[0029] Preferably X is an amino-alkyl group (e.g. -NH2 or -Ci-6alkyl-NH2), such as -(CH2)d-NH2 wherein d is from 0 to 5. Preferably d is from 2 to 4, and more preferably d is 3.

[0030] In some embodiments, a is 2 or 3, b is 0 or 1 , c is 1 or 2, R is H or Ci-e alkyl, and X is -NH2 or -Ci-6alkyl-NH2. As above, a+b+c =4.

[0031] In some embodiments, a is 2 or 3, b is 0 or 1 , c is 1 or 2, R is H or Ci-e alkyl, and X is -(CH2)d-NH2 wherein d is from 0 to 5. As above, a+b+c =4.

[0032] In some embodiments, a is 3, b is 0, c is 1 , R is H or Ci-e alkyl, and X is -(CH2)d-NH2 wherein d is from 2 to 4.

[0033] In some embodiments, a is 3, b is 0, c is 1 , R is H, methyl, ethyl or propyl, and X is -(CH2)s- NH2.

[0034] Preferably, the aminosilane used in the present invention is (3-aminopropyl)triethoxysilane or (3-aminopropyl)trimethoxysilane, more preferably (3-aminopropyl)triethoxysilane.

[0035] The aminosilane may be at least partially hydrolysed before use, e.g. in the coating composition. For example the aminosilane may be at least partially hydrolysed before being combined with the silica and any other components of the coating composition. In embodiments the aminosilane is partially hydrolysed in the coating composition. Thus, references herein to the aminosilane include a (partially) hydrolysed aminosilane.

[0036] The partially hydrolysed aminosilane may be in the form of an aminosilane oligomer or polymer. For example, the hydrolysed amino silane may be an oligomer or polymer having the following formula: are as defined above, and n is at least 2 (e.g. from 2 to 100, such as from 2 to 50 or from 2 to 10).

[0037] In embodiments the hydrolysed amino silane may be an oligomer or polymer having the following formula: are as defined above.

[0038] Hydrolysis may be achieved using water. For example, the aminosilane may be mixed with water for from about 1 to about 24 hours, such as from about 6 to about 12 hours. Hydrolysis may be conducted at a temperature of from about 20°C to about 95°C, such as from about 50°C to about 90°C, such as from about 75°C to about 85°C.

[0039] In some embodiments, the hydrolysed aminosilane is distilled. Distillation can be performed to remove e.g. water and / or ethanol. This can prevent reverse reaction with the hydrolysed aminosilane, thereby improving the stability of the hydrolysed aminosilane.

[0040] In some embodiments, the composition comprises from about 0.5 to about 10 wt% aminosilane, such as from about 1 to about 8 wt% or from about 1 to about 5 wt%.

[0041] Silica

[0042] The compositions and coatings described herein comprise silica.

[0043] The silica may be in the form of a powder, colloid or a sol. The silica may be nanosilica. For example, the silica may have a particle size of from about 1 to about 100 nm, such as from about 5 to about 90 m, from about 6 to about 60 nm or from about 6 to about 40 nm. In some embodiments, the composition comprises from about 1 to about 12 wt% silica, such as from about 1 to about 10 wt% or from about 1 to about 8 wt%.

[0044] The weight ratio of (i) aminosilane to (ii) silica may range from about 1 :1.5 to about 1 :12, such as from about 1:2 to about 1 :10, such as from about 1:2 to about 1 :8, from about 1 :2.5 to about 1:6, or from about 1:3 to about 1:4. The weight ratio of (i) aminosilane to (ii) silica may alternatively range from about 1:1.5 to about 1:5, such as from about 1 :2 to about 1:4. The weight ratio specified herein is the dry weight ratio, i.e. excluding any solvents such as water.

[0045] Water and other solvents

[0046] In addition to an aminosilane and silica, the composition also comprises water. In some embodiments, the composition comprises from about 10 to about 99 wt% water, such as from about 50 to about 98 wt%, from about 60 to about 97 wt%, from about 80 to about 96 wt% or from about 90 to about 96 wt%.

[0047] The water is present such that the weight ratio of (i) aminosilane to (iii) water is at least about 1:3, such as at least about 1:5, at least about 1:10, at least about 1 :18 or at least about 1:20. The water may be present such that the weight ratio of (i) aminosilane to (iii) water is less than about 1 :100, such as less than about 1:50, less than about 1:40 or less than about 1:30.

[0048] In embodiments the weight ratio of (i) aminosilane to (iii) water is from about 1:3 to about 1 : 100, from about 1 :5 to about 1 :50, from about 1 : 10 to about 1 :40 or from about 1 :20 to about 1:30.

[0049] In embodiments the composition comprises less than about 5 wt% ethanol, such as less than about 1 wt%, or less than about 0.1 wt%.

[0050] The composition is generally substantially free from non-aqueous solvents, e.g. the composition may comprise less than about 5 wt% of any non-aqueous solvents, such as less than about 1 wt%, less than about 0.5 wt% or less than about 0.1 wt%. The composition may be entirely free from non-aqueous solvents.

[0051] Other (optional) components The compositions described herein may consist of or consist essentially of aminosilane, silica and water.

[0052] The compositions and coatings described herein may also further comprise other optional components or additives, including surfactants, plasticizers, binders and / or pigments. In embodiments these are the only additional components present in the compositions other than aminosilane, silica and water.

[0053] For example, the composition may further comprise a surfactant, optionally wherein the surfactant is a silicone surfactant, such as a trisiloxane surfactant or a polyether modified siloxane. A suitable example is a polyether modified heptamethyltrisiloxane. If present, the surfactant is generally present in the amount of 5 wt% or less of the composition, such as from about 1 to about 5 wt% of the composition.

[0054] For example, a plasticizer can be used to improve coating characteristics, such as coating flexibility and toughness. If present, the plasticizer can be present in the amount of 5 wt% or less of the coating composition, such as from about 1 to about 3 wt% or from about 1 to about 2 wt%. Suitable plasticisers include Diisodecyl phthalate (DIDP), Diisononyl phthalate (DINP), Dibutyl sebacate (DBS, and combinations thereof.

[0055] Optionally, the formulation may comprise pigments to alter the aesthetic of the coating. These may include both organic and inorganic pigments. Organic pigments may include carbon black, alizarin, phthalocyanine, quinacridone etc and inorganic pigments may include titania, cobalt blue, mica, calcium carbonate, iron oxide etc. If present, pigments may be present in the amount of 5 wt% or less of the coating composition, such as from about 2 to about 5 wt% or from about 2 to about 4 wt%.

[0056] The coatings and composition may further comprise a binder selected from an organofunctionalsilane, hydrolysed organic silane, polyacrylic acid or a derivative thereof, polyurethane or a derivative thereof, or a mixture thereof.

[0057] The organofunctionalsilane may have the following structure: [X-(CH2)e]aSi(Ri)f(OR2)gwhere X is an organic group, such as mercapto, amino, hydroxy or vinyl; e is from 1 to 5; a is 1 or 2; f is from 0 to 2; g is from 1 to 3, with the proviso that a+f+g = 4; Ri is selected from methyl or ethyl and R2 is selected from methyl, ethyl or propyl. If present, polyacrylic acid may have a molecular weight of from about 350 to about 5,000, such as from about 1,000 to about 2,000. Polyacrylic acid derivative includes but limited to acrylates, methacrylate, acrylic esters, acrylic polymers.

[0058] If present, polyurethane may have a molecular weight of from about 500 to about 10,000, such as from about 1,000 to about 5,000.

[0059] If present, any additional binder is typically present in the amount of from about 0.01 to about 40 wt% of the coating composition, such as from about 0.1 to about 20 wt%.

[0060] In some embodiments the composition is substantially free from photocatalyst, e.g. the composition comprises less than about 1 wt% photocatalyst, such as less than about 0.5 wt% photocatalyst. In some embodiments the composition is free from any photocatalyst.

[0061] Substrate

[0062] The coating composition can be applied to any substrate. Preferably, the substrate is a metal such as aluminium, or a metal alloy such as steel.

[0063] In embodiments, the substrate is a conductor, an overhead conductor, a high-voltage conductor or power line.

[0064] Suitable overhead conductors include aluminium conductor steel reinforced ("ACSR") cables, aluminium conductor steel supported ("ACSS") cables, aluminium conductor composite core ("ACCC") cables, all aluminium alloy conductor ("AAAC") cables, and composite cables. The wires in the conductors can have a variety of cross sectional shapes including round and trapezoidal.

[0065] One or more pre-treatment processes may be used to prepare a surface of the conductor or one or more conductive wires for the coating. For example, the conductor or one or more conductive wires may be subjected to chemical treatment, pressurised air cleaning, hot water treatment, steam cleaning, brush cleaning, heat treatment, sand blasting, ultrasound, deglaring, solvent wipe, plasma treatment and the like.

[0066] In other embodiments the substrate is glass. In embodiments the substrate is a heat exchanger.

[0067] In embodiments the substrate is a plastic, such as polycarbonate, polyvinylchloride (PVC), polyolefins such as polypropylene and polyethylene, polyurethanes and thermoplastic polyurethanes (TPUs), thermoplastic elastomers (TPEs), and ethylene-vinyl acetate (EVA). In embodiments the substrate comprises biomedical tubing.

[0068] Method of forming coating

[0069] The coating composition can be applied to the substrate using a simple application technigue, such as by brushing, spraying or wiping the composition onto the conductor. In embodiments the composition is applied by spraying, such as spray drying.

[0070] The coating composition may be applied as a single coat. Alternatively, multiple coats (e.g. 2 or 3, such as 2) can be applied. When multiple coats are applied, each coat may be cured before the next coat is applied.

[0071] After application of the composition to the substrate the coating is cured or allowed to cure. This may comprise allowing the composition to cure by moisture curing. In embodiments, the curing process occurs at ambient temperature, i.e. the substrate is not actively heated. In embodiments, the temperature is maintained at below about 100°C, preferably below about 90°C, more preferably below about 80°C.

[0072] The composition may be cured for any period of time, such as from about 10 minutes to about 48 hours, such as from about 1 to about 36 hours, such as about 1 to about 24 hours or about 2 to about 6 hours.

[0073] It will be apparent that whilst new overhead conductors which are coated with a coating which reguires thermal curing can be subjected to a thermal curing step as part of the manufacturing process, thermal curing raises considerable practical and economic problems if seeking to retrofit an existing overhead conductor in situ with a composition which cures to form a coating for the overhead conductor. Indeed, it will be appreciated that in many circumstances it will be impractical to attempt to retrofit a large overhead conductor network by seeking to cure the applied coatings at a temperature of from 150°C up to 300°C for a time period of, for example, 24 hours. It is therefore extremely useful that the coating compositions of the present invention can be cured at ambient temperature. Coating

[0074] As discussed above, the aminosilane is generally hydrolysed, after which some or all of the silanol groups may condense or crosslink to form siloxane groups. Hydrolysis of an organosilane (e.g. an aminosilane) may therefore proceed as follows:

[0075] SiR2(OR)2+ H2O SiR2(OH)2+ 2 R-OH

[0076] SiR2(OH)2— > organosilane polymer or oligomer + 2 H2O — > organically modified silica or

[0077] SiR(OR)3+ H2O SiR(OH)3+ 3 R-OH

[0078] SiR(OH)3— > organosilane polymer or oligomer + 2 H2O — > organically modified silica

[0079] After application, a similar condensation or crosslinking reaction can then take place with the silica which is part of the claimed composition (i.e. which is mixed with the partially hydrolysed aminosilane) and the substrate. During this reaction bonds may be formed between the silica, the aminosilane and the substrate. Thus, the final coating on the substrate may comprise a matrix comprising amino-modified silica.

[0080] In one embodiment, the present invention is directed to a coating comprising silica (e.g. nanosilica) and amino-modified silica.

[0081] In one embodiment, the present invention is directed to a substrate (preferably an overhead conductor) comprising the coating described herein which comprises silica (e.g. nanosilica) and amino-modified silica.

[0082] The weight ratio of amino-modified silica to silica in the coating may be the same as the weight ratio ranges disclosed herein in relation to the aminosilane and silica starting materials. That is, the weight ratio of (i) amino-modified silica to (ii) silica in the coating may range from about 1:1.5 to about 1:12, such as from about 1:2 to about 1:10, such as from about 1 :2 to about 1 :8, from about 1 :2.5 to about 1 :6, or from about 1 :3 to about 1 :4. The weight ratio of (i) amino-modified silica to (ii) silica in the coating may alternatively range from about 1:1.5 to about 1:5, such as from about 1 :2 to about 1:4. In some embodiments, the mole ratio of (i) amino-modified silica to (ii) silica in the coating may range from about 1 :5 to about 1 :50, such as from about 1:5 to about 1:40, from about 1:5 to about 1:30 or from about 1 :5 to about 1 :15.

[0083] The final coating may have a thickness of less than about 1000 nm, such as less than about 750 nm, less than about 500 nm, less than about 300 nm or less than about 200 nm. The final coating may have a thickness of at least about 1 nm, at least about 2 nm, at least about 3 nm or at least about 5 nm. For example, the thickness of the coating may range from about 1 nm to about 500 nm, such as from about 2 nm to about 300 nm, or from about 5 nm to about 200 nm.

[0084] As discussed herein, the coating may be applied in multiple layers (e.g. 2, 3 or 4 layers). In this case, each layer may have the thickness of the coating described above, or this may be the total thickness of all the layers.

[0085] In embodiments (e.g. where the coating is applied as multiple layers), the total thickness of the coating (i.e. the total thickness of all the layers of the coating) may be up to about 10 pm, up to about 5 pm, up to about 3 pm, up to about 2 pm, up to about 1 pm, up to about 800 nm, up to about 500 nm or up to about 300 nm. For example, the total thickness of the coating may range from about 3 nm to about 10 pm, from about 5 nm to about 5 pm, from about 10 nm to about 1 pm, or from about 15 nm to about 500 nm.

[0086] Water contact angle

[0087] The water contact angle is a fundamental measure that characterizes the wetting properties of a material's surface. It is the angle formed between a water droplet and the solid surface at the point of contact. This angle provides insights into how a material interacts with water - whether it repels or attracts it. A high water contact angle (greater than 90 degrees) indicates hydrophobic behaviour, where water tends to bead up and roll off the surface. Conversely, a low water contact angle (less than 90 degrees) signifies hydrophilic behaviour, indicating that the surface promotes the spreading and wetting of water.

[0088] Mathematically, the water contact angle can be defined using Young's equation. Fundamentally the interaction of a liquid on a solid surface is governed by the competition among the liquid-vapor (y v), solid-liquid (YSL), and solid-vapor (ysv) interfacial tensions. Superhydrophilicity is achieved over a solid surface when the spreading coefficient (SSL ) is greater than or equal to zero as per Equation 1.

[0089] Equation 1: Spreading Coefficient as a Function of Interfacial Tensions

[0090] When SSLV < 0, the liquid forms droplet with a finite contact angle (0) at the solid surface.

[0091] The contact angle is defined as the angle between the solid surface plane and the tangent to the liquid surface.

[0092] Young’s Equation (Equation 2) refers to the ideal contact angle (0Y) and is only valid for a surface that is unaffected by depositing fluids and that are homogeneous, isotropic, smooth, and rigid.

[0093] Ysv ~ YSL cos 6Y

[0094] YLV

[0095] Equation 2: Young's Equation

[0096] The equilibrium state with the lowest Gibbs energy, indicating maximum stability, is linked to either Wenzel's state on a rough surface or Cassie's state on a heterogeneous surface. The Wenzel Equation is in Equation 3 and Cassie Equation, Equation 4. cos 01 / 17= r cos 6Y

[0097] Equation 3: Wenzel Equation

[0098] In the Wenzel Equation, r is the roughness parameter and eYis the ideal contact angle that would be measured on a flat surface of the same solid. This equation characterizes the most stable contact angle for stability when the liquid fully infiltrates the grooves of the rough surface, defining the 'homogeneous wetting' regime.

[0099] In the Cassie Equation f is the fractional area of a component the solid surface in combination with the Young’s contact angles for the two components. Wenzel and Cassie equations apply to surfaces whose protrusions and / or heterogeneities are small in comparison with the size of liquid / vapor interface. When the liquid remains on the surface without penetrating into the protrusions, residing over air pockets or a porous material like fabric, screen, membrane, etc., the Cassie equation undergoes modification, leading to the Cassie-Baxter equation (Equation 5). cos 6CB= r fscos 0 — (1 — fs) Equation 5: Cassie-Baxter Equation

[0100] Here, fs represents the fraction of the liquid base in contact with the solid surface (fs < 1), and (1 - fs) represents the fraction of the liquid base in contact with air pockets. The parameter ^denotes the roughness ratio of the solid in contact with the liquid. Since air is non-wetting with respect to water, the water / air contact angle is 180°. This equation anticipates an apparent contact angle for surfaces with diverse geometries and structures, where the liquid does not fully infiltrate the topography, a condition referred to as 'heterogeneous wetting'.

[0101] As shown by the above equations, it is evident that surface roughening, quantified by the roughness factor 'r,' diminishes the contact angle on hydrophilic materials, potentially causing complete water or liquid spreading. Conversely, roughening a hydrophobic surface raises the contact angle. In this scenario, a sizable water droplet remains elevated on the tops of asperities or other rough features.

[0102] As used herein, the term superhydrophobic refers to a surface having a contact angle with water of about 150° or more.

[0103] As used herein, the term hydrophobic refers to a surface having a contact angle with water of from about 90° to about 120°.

[0104] As used herein, the term hydrophilic refers to a surface having a contact angle with water of from about 10° to about 65°, such as from about 10° to about 55° or from about 10° to about 40°.

[0105] As used herein, the term superhydrophilic refers to a surface having a contact angle with water of 10° or less, preferably 5° or less, 4° or less, 3° or less, 2° or less or 1° or less.

[0106] In embodiments, the coating of the present invention has a water contact angle of 40° or less, such as 30° or less, 25° or less, 20° or less, 15° or less, 10° or less, 5° or less, 4° or less, 3° or less, 2° or less or 1° or less. In embodiments, the water contact angle of the coating increases by less than about 5°, such as less than about 4°, less than about 3°, less than about 2° or less than about 1 °, when the coating is (a) heated to about 100°C for a period of at least about 24 hours, (b) immersed in water for a period of at least about 24 hours, (c) immersed in an acidic solution having a pH of 3 or less for at least 24 hours, and / or (d) abraded with steel wool (e.g. about 50 times).

[0107] In embodiments, the water contact angle of the coating increases by less than about 5°, such as less than about 4°, less than about 3°, less than about 2° or less than about 1 °, when the coating is heated to about 100°C for a period of at least about 24 hours.

[0108] In embodiments, the water contact angle of the coating increases by about 25° or less, such as less than about 20°, or less than about 15°, when the coating is heated to about 150°C for a period of at least about 24 hours.

[0109] In embodiments, the water contact angle of the coating increases by about 25° or less, such as less than about 20°, or less than about 15°, when the coating is abraded with steel wool (e.g. about 50 times).

[0110] The water contact angle may be measured by applying a drop of water (e.g. about 50 microliters) to a substrate, and then the contact angle measured visually by taking a photograph and measuring the angle

[0111] Applications

[0112] Power Line Wet Audible Noise Reduction

[0113] Corona-induced wet audible noise on overhead power lines is a phenomenon associated with the presence of moisture on the insulating surfaces of these lines during wet weather conditions. Corona discharge occurs when the electric field at the surface of the conductors exceeds a critical value, leading to the ionization of air molecules. In the presence of moisture, the ionization process is enhanced, resulting in increased corona discharge and the generation of audible noise. The noise produced is characterized by a sizzling or crackling sound and is more pronounced when the power lines are wet. A corona discharge is an electrical discharge caused by the ionization of air surrounding a conductor carrying a high voltage. It represents a local region where the air (or other fluid) has undergone electrical breakdown and become conductive, allowing charge to continuously leak off the conductor into the air. It is often seen as a bluish glow in the air adjacent to metal conductors carrying high voltages and emits light by the same mechanism as a gas discharge lamp. Corona discharge has several unwanted effects which includes power loss and audible sounds.

[0114] The corona discharge on wet power lines is influenced by factors such as the surface conditions of conductors, conductor geometry, voltage levels, and atmospheric conditions. The presence of water on the conductor surfaces changes the electrical properties and increases the likelihood of corona discharge, leading to the audible noise. This phenomenon is not only an acoustic nuisance but can also have implications for the reliability and performance of power transmission systems.

[0115] Application of the composition or coating of the present invention to an overhead conductors reduces the water contact angle (due to the hydrophilic or superhydrophilic nature of the coating), reducing corona discharge and thus reducing power loss and corona sound.

[0116] Self-Cleaning Coatings

[0117] Superhydrophilic coatings play a pivotal role in imparting self-cleaning properties to paints by fostering an intense affinity for water, leading to a near- zero water contact angle. This unique characteristic ensures that when water comes into contact with a painted surface, it spreads uniformly rather than forming droplets. As the water spreads, it effectively collects and removes contaminants such as dust and dirt from the surface. The robust interaction between water molecules and the superhydrophilic coating not only facilitates the efficient removal of particles but also hinders their strong adhesion to the surface. Consequently, stains are prevented, and the painted surface remains cleaner for extended periods. The self-cleaning mechanism reduces the need for frequent manual cleaning and maintenance, making superhydrophilic-coated paints particularly advantageous in various applications, including architectural coatings and automotive paints, where a consistently clean and attractive appearance is desirable.

[0118] Antifogging shields, goggles and glass Superhydrophilic coatings contribute significantly to the effectiveness of antifogging shields, goggles, and glass by promoting optimal visibility in challenging conditions. When exposed to moist or humid environments, the superhydrophilic-coated surfaces encourage the condensation of water into a thin, uniform layer instead of forming obstructive fog droplets. This thin layer allows for transparency, ensuring clear vision through shields, goggles, or glass. The robust wettability of superhydrophilic coatings prevents the accumulation of water droplets, which can obstruct vision and impede clarity. The antifogging effect is particularly valuable in applications such as protective face shields, eyewear, and glass surfaces, where maintaining unobstructed visibility is crucial for safety and optimal functionality.

[0119] Heat Exchangers

[0120] In numerous thermal engineering applications, the control of liquid wetting behaviour is employed as a strategy to enhance heat transfer. The spreading of a liquid on a solid surface affects many thermal processes, such as boiling and evaporation, condensation and frosting and defrosting. Such coatings can be deployed in some processes of air- conditioning and power-generation systems, such as dehumidification, evaporative cooled condensers, and pool boiling at high heat flux.

[0121] For example, in nuclear power plants, as well as the cooling process of electronic devices, better wettability enhances critical heat flux (CHF) in pool boiling, which improves the reliability and performance of these systems. Another case is the condensation process, where a hydrophilic solid surface possesses a lower energy barrier for condensate nucleation and better drainage of the liquid phase, both of which have positive impact on heat and mass transfer. Slit-fin-and-tube heat exchangers were reported to have a significantly lower Fanning friction factor once the fins are treated to be hydrophilic, with no penalty on heat transfer. Thus, hydrophilicity can be preferred for its positive influence on thermal-hydraulic performance of a heat exchanger.

[0122] Frost formation on solid surfaces is also improved via the application of a hydrophilic or superhydrophilic surface. The morphology of liquid condensation on a solid surface is significantly influenced by wettability. Consequently, the early-stage structure of frost, formed from the frozen condensate, is largely dependent on the surface's wettability. Frost developing on a hydrophilic surface tends to be denser and thinner in its initial stages compared to frost on a hydrophobic surface. Furthermore, this hydrophilic frost exhibits higher thermal conductivity even during the later stages of growth. While superhydrophobic surfaces have the potential to delay the onset of frost formation, challenges related to contamination and long-term efficacy remain unresolved.

[0123] In the context of boiling, hydrophobicity proves advantageous for bubble nucleation, while hydrophilicity facilitates the departure of bubbles. The efficient spreading of the liquid becomes crucial, especially in scenarios involving high heat flux during boiling. Enhancing liquid rewetting on a superheated solid surface through hydrophilic treatment is recognized as a method to improve critical heat flux (CHF) in pool boiling situations. Likewise, in applications involving evaporative cooling, improved liquid spreading has the potential to generate a uniformly thin liquid film, thereby mitigating the occurrence of dry-out and enhancing mass transfer.

[0124] Antifouling

[0125] Anti-fouling coatings are essential for a wide range of industries. From a thermodynamic perspective, surface conditioning - the process of initial adhesion of biogenic macromolecules free in the water column, or released by animals / plants for attachment, is driven by the loss of Gibbs free energy AGads ( Gads < 0). Gibbs free energy, at constant temperature and pressure, can be defined as AGads = AHads - T ASads, where AHads and ASads denote adsorption enthalpy and entropy respectively.

[0126] To minimize the loss of Gibbs free energy and thus reduce adsorption at the surface-water interface, a putative fouling-resistant coating should minimize the increase of entropy whilst still providing a high enthalpy component.

[0127] Based on this principle, research in recent years has focused on the development of novel hydrophilic materials including (super)hydrophilic surfaces on which water spreads completely, and that exhibit close to zero contact angle. Hydrophilic surfaces are known for their fouling-resistant properties, which are exploited in the biomedical field to protect surfaces from cell adhesion and the non-specific adsorption of proteins. A less-explored application of hydrophilic surfaces concerns their use in the prevention of marine biofouling. These materials are designed to manifest tightly bound water layers at the surface, providing high enthalpy of hydration to physically and energetically interfere with the adsorption of biomolecules. Additionally, different functional groups have previously been assessed for their resistance to protein adsorption, and it was concluded that the best performing chemistries should not only be well-hydrated, but also neutrally charged and capable of accepting hydrogen bonds. Biomedical

[0128] Most medical device consumable surfaces are not inherently hydrophilic and need to be treated with hydrophilic coatings. Commonly used coating materials include polyvinylpyrrolidone (PVP), polyvinylalcohol (PEO), polyacrylic acid (PAA) etc, which can attract and retain moisture to give the surfaces lubricating quality, thereby reducing the potential trauma caused by consumables entering the human body, improving the performance of these invasive procedures, and reducing protein adsorption, reducing platelet activation at the same time. At present, hydrophilic coatings are mainly used in interventional medical devices of the cardiovascular, circulatory, nervous, urinary and vascular system, which include the inner and outer surfaces of stents, separators, lenses, guide wires, needles, implants, balloons, vascular access, urinary catheters, catheters, etc.

[0129] There is a significant potential for superhydrophilic coatings in biomedical applications. Superhydrophilic poly(l-lactic acid) electrospun membrane, obtained by argon and oxygen plasma treatment is already developed for biomedical applications, however this does not involve facile application methods.

[0130] The coatings and composition of the invention can therefore be applied to biomedical devices, such as those listed above.

[0131] Examples

[0132] 10g of hydrolysed (3-aminopropyl)triethoxysilane was diluted with 90 g of distilled water.

[0133] In a separate vessel, a dispersion was made using nanosilica powder (synthetic amorphous pyrogenic silica, CAS No. 112945-52-5) in water (1 :10-20) using mechanical disperser at 1500 rpm for 30 min.

[0134] Hydrophilic coating solutions were prepared by adding different amounts (30-180 g) of the silica dispersions to 100g of the diluted hydrolysed aminosilane sol, followed by mixing for 10 min. The final compositions prepared (Compositions 1-5) are set out in the table below.

[0135] Table 1 - composition of the hydrophilic coating solutions prepared

[0136] All coating compositions were sprayed onto Al-panels (6 pm Ra surface roughness profile) and dried at ambient temperature for 24 hours.

[0137] Example 2 - Contact Angle measurement

[0138] 50 microliters of water (1 drop) was placed on the panels formed in Example 1 after 24h of curing. The contact angle was then measured visually by taking a photograph and measuring the angle. The results are shown in Table 2 below.

[0139] Table 2 - water contact angle measurements

[0140] Example 3 - Durability testing

[0141] The panels treated with compositions 3, 4 and 5 were then subjected to the testing outlined below.

[0142] Example 3a - Heat Stability

[0143] A coated panel was kept in an oven at 100°C for 24 hrs. After 24 hours, the panel was removed from the oven, cooled to room temperature and the water drop contact angle was measured. The water contact angle was 10° for the substrate treated with composition 3, 1° for the substrate treated with composition 4 and 3° for the substrate treated with composition 5.

[0144] A coated panel was kept in an oven at 150°C for 24 hrs. After 24 hours, the panel was removed from the oven, cooled to room temperature and the water drop contact angle was measured. The water contact angle was 25° for the substrate treated with composition 3, 15° for the substrate treated with composition 4 and 20° for the substrate treated with composition 5.

[0145] Example 3b - Temperature cycle test:

[0146] A coated panel was kept in an oven at 100°C for 24 hrs. After 24 hours, the panel was removed from the oven, then cooled at room temperature. The panel was then placed in an oven at 100°C for a further 24 hrs. This process was continued until the panel had been heated and cooled 5 times. The water drop contact angle was measured again. Contact angles were similar to those shown in Table 2.

[0147] Example 3c - Water Immersion Stability

[0148] A coated panel was immersed in water for 72 hrs. After 72 hours, the panel was removed from the water, dried at room temperature and the water drop contact angle was measured. Contact angles were similar to those shown in Table 2.

[0149] Example 3d - Acid Immersion Stability

[0150] A coated panel was immersed into acidic solution (pH= 3) for 72 hrs. After 72 hours, the panel was removed from the acid solution, dried at room temperature and the water drop contact angle was measured. Contact angles were similar to those shown in Table 2.

[0151] Example 3e - Abrasion Test

[0152] Qualitative abrasion test was carried out as following.

[0153] Composition 4 was applied onto an Al-panel (6 pm profile) through spraying, and then cured at ambient temperature for 24h. After 24h, the panel was rubbed with abrasive cloths 50 times and then with steel wool for another 50 times. The excess deposit on the metal surface is removed. Then, water drop contact angle was measured on the bare metal surface. Contact angles were similar to those shown in Table 2.

[0154] Example 4

[0155] Example 4a - coating preparation

[0156] 40g of APTES [(3-aminopropyl)triethoxysilane] was mixed with 100g of water and kept in a water bath for 12h at 80°C. The solution was then cooled and transferred to a closed container.

[0157] 20g of synthetic amorphous pyrogenic silica (CAS No. 112945-52-5) was added to a steel container of a high-speed disperser. 280g of distilled water was added and the silica dispersed at 3000 rpm for 30 min. The silica was then transferred into a closed container.

[0158] 10 g of hydrolysed APTES was diluted with 90g of distilled water and mixed very well using HSD at 1500 rpm for 10 min. 150g of silica was added very slowly and under mixing. The disperser speed was increased slowly to 3000 rpm.

[0159] The mixing was continued for another 30 min and the product was transferred to a closed container before being applied onto Al-panels (6 pm profile) through spray coating and cured at ambient temperature for 24h.

[0160] The water contact angle was measured at ambient temperature, after heating to 100°C, after heating to 150°C, and after scrubbing with steel wool (as described above in relation to Example 3).

[0161] The same testing was also performed on identical panels which had been treated with other superhydrophilic coatings, as shown in the table below.

[0162] Table 3 - coating compositions

[0163] The water contact angle was then measured, with results shown in the table below.

[0164] Table 4 - water contact angle measurements

[0165] Example 5

[0166] Example 5a - coating preparation

[0167] Hydrolysed APTES [(3-Aminopropyl)triethoxysilane]:

[0168] 400g of APTES was mixed with 1 ,000g of water and kept in a water bath for 12h at 80°C.

[0169] The mixture was then cooled and transferred to a closed container. Distillation of Hydrolysed APTES [(3-Aminopropyl)triethoxysilane]:

[0170] 1,400 g of hydrolysed APTES was added to a 2 L round bottom glass flask fitted with distillation head, condensing tube and a thermometer. The flask was then placed over a magnetic heating mantle and heated until the liquid was boiling. Stirring was continued using a magnetic stirrer throughout the process. Distillation started at around 80°C and continued up to about 98-100°C. The distillate, which was an azeotropic mixture of ethanol and water, was collected.

[0171] After collecting 390 g of distillate the heating was stopped, and the mixture cooled to ambient temperature before being stored in an air-tight container.

[0172] This distillation step is not essential, but can help to prevent the reverse reaction and hence provide a better shelf life of the distillate.

[0173] Preparation of nano-silica dispersion:

[0174] 200g of synthetic amorphous pyrogenic silica (CAS No. 112945-52-5) was added in the steel container of high-speed disperser. 2,800g of distilled water was added, and the silica was dispersed at 2500 to 3000 rpm for 30 min. The silica was then transferred into a closed container.

[0175] Coating formulation:

[0176] 100 g of hydrolysed APTES or distilled APTES was diluted with 900g of distilled water and mixed very well using HSD at 1500 rpm for 10 min. 1 ,500g of silica was added very slowly under dispersion. The disperser speed was increased slowly to 1500-2000 rpm.

[0177] The dispersion was continued for another 30 min and the product transferred into a close container. The composition was then applied to an aluminium substrate.

[0178] Example 5b - comparative composition preparation

[0179] N-(2-aminoethyl)-3-aminopropyltriethoxysilane was obtained from Sigma Aldrich and oligomerized in a laboratory by adding a quantitative amount of water followed by hydrolysis and distillation. Nano silica sol was obtained from Sigma Aldrich with brand name Ludox.

[0180] 10g of AEAOS oligomer was added to 90 g of Ludox silica sol and reacted at 50°C for 3 hours with constant stirring. The product was then diluted with DI water to a concentration of 60% and then applied to the same type of aluminium substrate as in Example 5a.

[0181] Example 5c - results

[0182] The water contact angle of the coated substrates made in Examples 5a and 5b were then measured at ambient temperature, after heating to 100°C for 72 hours, after immersion in water for 72 hours, and after rubbing with abrasive cloths 50 times and then with steel wool for another 50 times. The results are set out below.

[0183] Table 5 - water contact angle measurements

[0184] Example 6

[0185] Example 6a - coating preparation

[0186] Hydrolysed APTES [(3-Aminopropyl)triethoxysilane]:

[0187] 400g of APTES was mixed with 1 ,000g of water and kept in a water bath for 12h at 80°C. The mixture was then cooled and transferred to a closed container.

[0188] Distillation of Hydrolysed APTES [(3-Aminopropyl)triethoxysilane]:

[0189] 1,400 g of hydrolysed APTES was added to a 2 L round bottom glass flask fitted with distillation head, condensing tube and a thermometer. The flask was then placed over a magnetic heating mantle and heated until the liquid was boiling. Stirring was continued using a magnetic stirrer throughout the process. Distillation started at around 80°C and continued up to about 98-100°C. The distillate, which was an azeotropic mixture of ethanol and water, was collected.

[0190] After collecting 390 g of distillate the heating was stopped, and the mixture cooled to ambient temperature before being stored in an air-tight container.

[0191] This distillation step is not essential, but can make the reaction irreversible and also allow polymerization among aminosilane molecules.

[0192] Preparation of nano-silica dispersion:

[0193] 200g of colloidal silica (CAS No. 7631- 86-9, avg particle size ~12 nm) powder from West System was added in the steel container of high-speed disperser. 2,800g of distilled water was added, and the silica was dispersed at 2500 to 3000 rpm for 30 min. The colloidal silica was then transferred into a closed container.

[0194] Coating formulation:

[0195] Hydrophilic coating solutions were prepared by adding different amounts (90-180 g) of the silica dispersions to 100g of the diluted hydrolysed aminosilane sol, followed by mixing for 10 min. The final compositions prepared (Compositions 6a1 , 6a2 and 6a2) are set out in the table below (see Table 6).

[0196] Table 6 - Composition of the Hydrophilic Coating Solutions Prepared

[0197] Comparative Example 6b2: poly (acrylic acid) aqueous solution was prepared as directed in Polymers 2023, 15, 1242. Then, PAA aqueous solution was slowly added into a predetermined amount of hydroxylated SiC>2 colloidal suspension (LUDOX TM-40) to prepare PAA / SiO2 dispersions. Comparative Example 6b3: KR101848195 presented a hydrophilic coating formulation through APTES (3-aminopropyltriethoxysilane) hydrolysis. According to sample A1S2E preparation, 16g of APTES was added with 20 g of water and stirred well for 10 min and hydrolysed for 10 min at 70°C. The colloidal silica with particle size (avg) 15 nm was added into the hydrolysed APTES with a ratio APTES : colloidal silica : H2O of 16:32:20.

[0198] The coating mixtures of Comparative Examples 6b1 , 6b2 and 6b3 were applied onto Al- panels (6 pm RA surface roughness profile) and dried at ambient temperature for 24 hours.

[0199] Example 6c - results

[0200] 50 microliters of water (1 drop) were placed on the panels formed in Examples 6a1-3 and 6b1-3 after 24h of curing. The contact angle was then measured visually by taking a photograph and measuring the angle. The results are shown in Table 7 below.

[0201] Table 7 - water contact angle measurements

[0202] The panels treated with Example 6a2 and Comparative Example 6b3 were then subjected to the testing outlined above in Examples 3a-3e, with the results shown below in Table 8.

[0203] Table 8 - water contact angle after various tests As shown above, the compositions of the invention produce a superhydrophilic coating, which retains its superhydrophilic properties even after exposure to, for example, heat, water or abrasive forces.

[0204] Embodiments

[0205] 1. A coating composition comprising (i) an aminosilane, (ii) silica, and (iii) water; wherein the weight ratio of (i) aminosilane to (ii) silica is from about 1:1.5 to about 1:12; and wherein the weight ratio of (i) aminosilane to (iii) water is at least about 1:3, such as from about 1:3 to about 1 :100, from about 1 :5 to about 1:50, from about 1:10 to about 1:40 or from about 1:20 to about 1:30.

[0206] 2. The coating composition of embodiment 1, wherein the composition comprises from about 0.5 to about 10 wt% aminosilane, such as from about 1 to about 8 wt% or from about 1 to about 5 wt%.

[0207] 3. The coating composition of any preceding embodiment, wherein the composition comprises from about 1 to about 12 wt% silica, such as from about 1 to about 10 wt% or from about 1 to about 8 wt%.

[0208] 4. The coating composition of any preceding embodiment, wherein the aminosilane is at least partially hydrolysed and distilled.

[0209] 5. The coating composition of any preceding embodiment, wherein the aminosilane has the formula Si(OR)a(R)b(X)c, wherein R is any suitable organic group, X contains an amino group, a is from 1 to 3, b is from 0 to 2, and c is from 1 to 3, with the proviso that a+b+c =4.

[0210] 6. The coating composition of embodiment 5, wherein b is 0 or 1, such as wherein b is 0.

[0211] 7. The coating composition of embodiment 5 or 6, wherein a is 2 or 3, such as wherein a is 3.

[0212] 8. The coating composition of any of embodiments 5-7, wherein c is 1 or 2, such as wherein c is 1.

[0213] 9. The coating composition of any of embodiment 5-8, wherein R is H or an alkyl group, optionally wherein R is selected from H, methyl, ethyl or propyl, such as wherein R is ethyl. 10. The coating composition of any of embodiment 5-9, wherein X is an amino-alkyl group, optionally wherein X is -(CH2)d-NH2, wherein d is from 0 to 5, such as from 2 to 4 or wherein d is 3.

[0214] 11 . The coating composition of any preceding embodiment, wherein the aminosilane is (3-aminopropyl)triethoxysilane or (3-aminopropyl)trimethoxysilane, preferably wherein the aminosilane is (3-aminopropyl)triethoxysilane.

[0215] 12. The coating composition of any preceding embodiment, wherein the composition further comprises a binder selected from an organofunctionalsilane, hydrolysed organic silane, polyacrylic acid or a derivative thereof, polyurethane or a derivative thereof, or a mixture thereof.

[0216] 13. The coating composition of embodiment 12, wherein the organofunctionalsilane has the following structure: [X-(CH2)e]aSi(Ri)f(OR2)gwhere X is an organic group, such as mercapto, amino, hydroxy or vinyl; e is from 1 to 5; a is 1 or 2; f is from 0 to 2; g is from 1 to 3, with the proviso that a+f+g = 4; Ri is selected from methyl or ethyl and R2 is selected from methyl, ethyl or propyl.

[0217] 14. The coating composition of any preceding embodiment, wherein the silica is nanosilica.

[0218] 15. The coating composition of any preceding embodiment, wherein the silica is in the form of a powder, colloid or a sol having an average particle size of from about 5 to about 90 nm.

[0219] 16. The coating composition of any preceding embodiment, wherein the composition further comprises a surfactant, optionally wherein the surfactant is a silicone surfactant, such as wherein the surfactant is a trisiloxane surfactant, such as a polyether modified siloxane.

[0220] 17. The coating composition of embodiment 16, wherein the surfactant is present in the amount of from about 1 to about 5 wt% of the composition.

[0221] 18. The coating composition of any preceding embodiment, wherein the composition further comprises a plasticizer, optionally wherein the plasticizer is selected from diisodecyl phthalate (DIDP), diisononyl phthalate (DINP), dibutyl sebacate (DBS), and combinations thereof. The coating composition of embodiment 18, wherein the plasticizer is present in the amount of from about 1 to about 5 wt% of the composition. The coating composition of any preceding embodiment, wherein the composition further comprises a pigment, optionally wherein the pigment is an organic pigment selected from carbon black, alizarin, phthalocyanine, or quinacridone etc, or an inorganic pigment selected from titania, cobalt blue, mica, calcium carbonate, or iron oxide. The coating composition of embodiment 20, wherein the pigment is present in the amount of from about 1 to about 5 wt% of the composition. A hydrophilic or superhydrophilic coating formed using the composition of any preceding embodiment. A hydrophilic or superhydrophilic coating comprising (i) amino-modified silica and (ii) silica; wherein the weight ratio of (i) amino-modified silica to (ii) silica is from about 1:1.5 to about 1 :12. The coating of embodiment 22 or 23, wherein the coating has a water contact angle of about 20° or less, about 15° or less, about 10° or less, about 5° or less, about 4° or less, about 3° or less, about 2° or less or about 1° or less. The coating of any of any of embodiments 22-24, wherein the water contact angle of the coating increases by less than about 5°, such as less than about 4°, less than about 3°, less than about 2° or less than about 1°, when the coating is (a) heated to about 100°C for a period of at least about 24 hours, (b) immersed in water for a period of at least about 24 hours, (c) immersed in an acidic solution having a pH of about 3 or less for at least about 24 hours, and / or (d) abraded with steel wool. A substrate comprising the coating of any of embodiment 22-25, preferably wherein the substrate is an overhead conductor. 27. A method of forming a hydrophilic or superhydrophilic coating, the method comprising applying the composition of any of embodiments 1-21 to a substrate.

[0222] 28. The method of embodiment 27, wherein the method further comprises allowing the composition to cure.

[0223] 29. The method of embodiment 28, wherein the step of allowing the composition to cure comprises allowing the composition to cure solely by moisture curing; and / or wherein the step of allowing the composition to cure does not involve heating the composition above ambient temperature; and / or wherein the step of allowing the composition to cure comprises maintaining the temperature of the composition and the coating being formed on the overhead conductor below about 100°C, preferably below about 90°C, more preferably below about 80°C; and / or wherein the curing process lasts from about 1 to about 48 hours.

[0224] 30. The method of any of embodiments 27-29, wherein the composition is applied by spray drying.

[0225] 31. The method of any of embodiments 27-30, wherein the substrate is an aluminium substrate.

[0226] 32. The method of any of embodiments 27-31 , wherein the substrate is an overhead conductor.

[0227] 33. A method for reducing corona noise, the method comprising applying the composition of any of embodiments 1-21 to a substrate.

[0228] 34. Use of the coating composition of any of embodiments 1-21, or the coating of any of embodiments 22-25, to reduce corona noise from an overhead conductor.

[0229] 35. A kit for forming the composition of any of embodiments 1-21 , the kit comprising: a first part comprising an aminosilane or a hydrolysed aminosilane; and a second part comprising silica; wherein, in use, the first and second parts are mixed together to form the composition.

Claims

Claims1. A coating composition comprising (i) an aminosilane, (ii) silica, and (iii); wherein the weight ratio of (i) aminosilane to (ii) silica is from about 1:1.5 to about 1 :12; and wherein the weight ratio of (i) aminosilane to (iii) water is at least about 1 :3.

2. The coating composition of claim 1 , wherein the composition comprises from about 0.5 to about 10 wt% aminosilane, such as from about 1 to about 8 wt% or from about 1 to about 5 wt%.

3. The coating composition of any preceding claim, wherein the composition comprises from about 1 to about 12 wt% silica, such as from about 1 to about 10 wt% or from about 1 to about 8 wt%.

4. The coating composition of any preceding claim, wherein the aminosilane is at least partially hydrolysed.

5. The coating composition of any preceding claim, wherein the aminosilane has the formula Si(OR)a(R)b(X)c, wherein R is any suitable organic group, X contains an amino group, a is from 1 to 3, b is from 0 to 2, and c is from 1 to 3, with the proviso that a+b+c =4.

6. The coating composition of claim 5, wherein b is 0 or 1 , such as wherein b is 0; wherein a is 2 or 3, such as wherein a is 3; and / or wherein c is 1 or 2, such as wherein c is 1.

7. The coating composition of any of claims 5-6, wherein R is H or an alkyl group, optionally wherein R is selected from H, methyl, ethyl or propyl, such as wherein R is ethyl.

8. The coating composition of any of claims 5-7, wherein X is an amino-alkyl group, optionally wherein X is -(CH2)d-NH2, wherein d is from 0 to 5, such as from 2 to 4 or wherein d is 3.

9. The coating composition of any preceding claim, wherein the aminosilane is (3- aminopropyl)triethoxysilane or (3-aminopropyl)trimethoxysilane, preferably wherein the aminosilane is (3-aminopropyl)triethoxysilane.

10. The coating composition of any preceding claim, wherein the silica is nanosilica.

11. The coating composition of any preceding claim, wherein the silica is in the form of a powder, colloid or a sol having an average particle size of from about 5 to about 90 nm.

12. A hydrophilic or superhydrophilic coating formed using the composition of any preceding claim.

13. A hydrophilic or superhydrophilic coating comprising (i) amino-modified silica and (ii) silica; wherein the weight ratio of (i) amino-modified silica to (ii) silica is from about 1:1.5 to about 1 :12.

14. The coating of claim 12 or 13, wherein the coating has a water contact angle of about 20° or less, about 15° or less, about 10° or less, about 5° or less, about 4° or less, about 3° or less, about 2° or less or about 1° or less.

15. The coating of any of claims 12-14, wherein the water contact angle of the coating increases by less than about 5°, such as less than about 4°, less than about 3°, less than about 2° or less than about 1°, when the coating is (a) heated to about 100°C for a period of at least about 24 hours, (b) immersed in water for a period of at least about 24 hours, (c) immersed in an acidic solution having a pH of about 3 or less for at least about 24 hours, and / or (d) abraded with steel wool.

16. A substrate comprising the coating of any of claims 12-15, preferably wherein the substrate is an overhead conductor.

17. A method of forming a hydrophilic or superhydrophilic coating, the method comprising applying the composition of any of claims 1-11 to a substrate.

18. The method of claim 17, wherein the method further comprises allowing the composition to cure.

19. The method of claim 18, wherein the step of allowing the composition to cure comprises allowing the composition to cure solely by moisture curing; and / orwherein the step of allowing the composition to cure does not involve heating the composition above ambient temperature; and / or wherein the step of allowing the composition to cure comprises maintaining the temperature of the composition and the coating being formed on the overhead conductor below about 100°C, preferably below about 90°C, more preferably below about 80°C; and / or wherein the curing process lasts from about 1 to about 48 hours.

20. The method of any of claims 17-19, wherein the composition is applied by spray drying.

21. The method of any of claims 17-20, wherein the substrate is an aluminium substrate.

22. The method of any of claims 17-21, wherein the substrate is an overhead conductor.

23. A method for reducing corona noise, the method comprising applying the composition of any of claims 1-11 to a substrate.

24. Use of the coating composition of any of claims 1-11 , or the coating of any of claims 22-25, to reduce corona noise from an overhead conductor.

25. A kit for forming the composition of any of claims 1-11, the kit comprising: a first part comprising an aminosilane or a hydrolysed aminosilane; and a second part comprising silica; wherein, in use, the first and second parts are mixed together to form the composition.

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