WO2013042052A1 - Superhydrophobic coatings and methods of preparation - Google Patents

Abstract

In various embodiments, the present invention provides a coating composition comprising a base resin and particle fillers of varying sizes, where the particle fillers are covalently or hydrogen bond grafted with organofunctional siloxanes of varying molecular weight (or varying chain lengths) and functionality, for example in a dilute solution in an organic solvent. Coating compositions of the present invention can be superhydrophobic and self-cleaning.

Description

SUPERHYDROPHOBIC COATINGS AND METHODS OF PREPARATION

BACKGROUND

[0001] Hydrophobic properties are desirable for many applications. For example, a durable, hydrophobic coating would be desirable for the high voltage industry to inhibit flashover on insulators, and to inhibit icing on conductors, insulators, and tower structures, corona-induced noise reduction on conductors and refurbishment of undersized sub-station insulators, for the microelectromechanical systems and microfluidics industry to inhibit constriction, for the biomedical industry to inhibit fouling or microbial contamination, and for counteracting corrosion and biofouling of metals in marine and freshwater vessels, rainwater harvesting on roofing structures, icing on structures such as wind turbine blades, and the like.

[0002] In the case of the high voltage industry, the bulk of power delivery from power generating sites to load centers is carried out by overhead distribution and transmission lines. To reduce line losses, power transmission over such transmission lines is often carried out at AC or DC high voltages on the order of 1 kV to 1 ,000 kV. High voltage line conductors are physically attached to support structures, yet the conductors also have to be electrically isolated from the support structures. The device that performs the dual functions of mechanical support and electrical isolation is referred as a high voltage insulator. Superhydrophobic self-cleaning properties would serve to inhibit the accumulation of contaminants on a surface of the insulator, which can produce a conductive layer when wet that can lead to leakage currents, dry band arcing, and ultimately flashover. Due to self- cleaning properties of some superhydrophobic surfaces, contaminants that are deposited on the surface of the insulator would be readily picked up by water droplets falling or condensed on the surface. In addition, a superhydrophobic self-cleaning surface would inhibit the formation of ice on conductors, insulators, and support structures. These structures have been known to collapse under the weight of ice.

[0003] Self-cleaning superhydrophobic coatings as anti-pollution coatings for high voltage equipment have been suggested by Li et al. (US 7,722,951 and US 8,206,776) but they suggest processes such as using plasma etching of PTFE and plasma fluorination of polybutadiene, which are not suitable for covering large convoluted surfaces, as well as sacrificial templating, removal of eutectic liquids used as solvents after gelation, and sol-gel methods. However, such methods are complex. [0004] It is against this background that a need arose to develop the simple, cost- effective superhydrophobic self-cleaning coatings and related methods and coated objects described herein.

SUMMARY

[0005] In various embodiments, the present invention provides a coating composition comprising a base resin and particle fillers of varying sizes, where the particle fillers are covalently or hydrogen bond grafted with organo functional siloxanes of varying molecular weight (or varying chain lengths) and functionality, for example in a dilute solution in an organic solvent. Without restricting the present invention to any particular mechanism, is believed that the grafted particle fillers migrate to an outer surface of a resulting coating due to the incompatibility and phase-separation between grafted siloxane moieties and hydrocarbon moieties within the base resin. The rapid evaporation of the solvent during the spraying process also assists in creating the three dimensional hierarchical structure at the surface. The coating composition can be applied as a "one-pot" formulation, and can be cured at an elevated temperature using a thermally activated catalyst or at or near room temperature using an UV photocatalyst or another type of catalyst.

[0006] In various embodiments, the resulting coating has a three-dimensional hierarchical structure which provides superhydrophobic, self-cleaning, anti-fouling, anti-icing, anti-dragging, anti-corrosion, hardness, and abrasion-resistant properties. Once cured, an outer surface of the coating is enriched in grafted particle fillers, including micron-sized and nano-sized particles, providing a three-dimensional roughness along with, or coated in, siloxane that is covalently or hydrogen bonded to both the particle fillers and a phase- separated base resin within the bulk of the coating.

[0007] Other aspects and embodiments of the invention are also contemplated. The foregoing summary and the following detailed description are not meant to restrict the invention to any particular embodiment but are merely meant to describe some embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] For a better understanding of the nature and objects of some embodiments of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings. [0009] FIG. 1 is a schematic of a siloxane-enriched surface of a coating in which a siloxane moiety is phase-separated from a hydrocarbon moiety within the bulk of the coating, according to an embodiment of the invention.

[0010] FIG. 2 is a schematic of an aminofunctional siloxane grafted onto the nano- or micron-sized oxide particles through hydroxyl groups on a surface of the particle, via hydrogen or covalent bonds, according to an embodiment of the invention.

[0011] FIG. 3 is a schematic of the cross-sectional view through a 3-dimensional hierarchical surface of a coating with bi-plurality nano-scale roughness on high aspect ratio micron scale roughness, fully covered by a layer of low surface energy siloxane which is also copolymerized with a base hydrocarbon resin through hydrolytically stable Si-C bonds, according to an embodiment of the invention.

[0012] FIG. 4 is a schematic of the cross-sectional view through a 3-dimensional hierarchical surface of a coating with bi-plurality nano-scale roughness on low aspect ratio micron scale roughness, fully covered by a layer of low surface energy siloxane which is also copolymerized with a base hydrocarbon resin through hydrolytically stable Si-C bonds, according to an embodiment of the invention.

[0013] FIG. 5 is a schematic of the use of linker moieties such as silanes or phosphonates between particles and di-functional or multi-functional siloxanes, such that grafted particles are covalently bonded to the siloxanes and therefore to a base hydrocarbon resin which could be an epoxy or an acrylic homopolymer or copolymer, according to an embodiment of the invention.

[0014] FIG. 6 is a SEM micrograph at 500 times magnification, bar equals 20 microns of a coating sample applied using spin coating and showing the distinct surface protuberances and spaces between them of 20 and 50 microns in accordance with an embodiment of the invention.

[0015] FIG. 7 is a SEM micrograph using an Everhard-Thornley detector (ETD) at 500 times magnification, bar equals 200 microns, of a coating sample applied using spray coating and showing the distinct surface roughness with a thin surface polymer covering in accordance with an embodiment of the invention.

[0016] FIG. 8 is a SEM micrograph of the same sample in Fig. 7 using a backscattered detector at 600 times magnification (bar equals 100 microns) of a coating sample applied using spray coating and showing the enhanced surface roughness in accordance with an embodiment of the invention. [0017] FIG. 9 is a SEM micrograph with a TLD at 10,000 times magnification (bar equals 10 microns) of a coating sample applied using spray coating and showing the distinct surface roughness with low aspect ratio primary alumina-silicate micron-sized particles, where the spacing between the round asperities is about 5 microns, in accordance with Example 5 of the invention.

[0018] FIG.10 is a SEM micrograph with an ETD at 10,000 times magnification (bar equals 10 microns) of a coating sample applied using spray coating and showing the distinct surface roughness with high aspect ratio primary Si0₂ micron-sized: fillers, with deep chasm about 3 microns wide, in accordance with Example 6 of the invention.

[0019] FIG.11 is a SEM micrograph at 2,000 times magnification (bar equals 50 microns) of a coating sample applied using spray coating and showing the typical coating thickness of 40 microns in a single layer coating on a glass slide, in accordance with Example 5 of the invention.

[0020] FIG.12 is a SEM micrograph with an TLD at 100,000 times magnification (bar equals 1 micron) of a coating sample applied using spray coating and showing the distinct outer surface polymeric covering , in accordance with most embodiments of the invention.

[0021] FIG.13 is a SEM micrograph with an ETD at 2,000 times magnification (bar equals 50 microns) of a coating sample applied using spray coating from a mixture of solvents and vastly enhanced surface roughness as a result of the differential evaporation of the different boiling point solvents, in accordance with embodiment 8 of the invention.

[0022] FIG.14 shows SEM micrographs with a back-scattered detector at 2,000 and 10,000 times magnification (bar equals 50 and 10 microns respectively) of a very high aspect ratio naturally mined, primary micron-sized aluminosilicate particle, in accordance with Example 9 of the invention.

[0023] Fig. 15 shows an overlaid image from a light microscope image at 1,200 times magnification, indicating the homogeneity of surface roughness, in accordance with most embodiments of this invention.

[0024] Fig. 16 shows resistance measurement recovery over time (averaged values) of a comparison of HTV silicone rubber and the superhydrophobic nano-structured coatings after exposure to salt pollution. The upper curve corresponded to the ESDD level 0.15 mg/cm², while the lower curve corresponded to ESDD 0.45 mg/cm². Due to the large difference in scales between the HTV- and nano-composite material coated samples the recovery of HTV samples is not clearly evident. [0025] Fig. 17 shows spray application of the coatings onto distribution voltage F- neck line-post insulators and a porcelain cap-and-pin insulator.

DETAILED DESCRIPTION

Definitions

[0026] The following definitions apply to some of the aspects described with regard to some embodiments of the invention. These definitions may likewise be expanded upon herein.

[0027] As used herein, the singular terms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to an object can include multiple objects unless the context clearly dictates otherwise.

[0028] As used herein, the term "and/or" in reference to two or more materials, processes, etc., refers to each material/process individually or in any combination. For example, "A and/or B" refers to "A" individually, or in the alternative, "B" individually, or both "A" and "B" together.

[0029] As used herein, the term "set" refers to a collection of one or more objects. Thus, for example, a set of objects can include a single object or multiple objects. Objects of a set can also be referred to as members of the set. Objects of a set can be the same or different. In some instances, objects of a set can share one or more common characteristics.

[0030] As used herein, the term "adjacent" refers to being near or adjoining. Adjacent objects can be spaced apart from one another or can be in actual or direct contact with one another. In some instances, adjacent objects can be connected to one another or can be formed integrally with one another.

[0031] As used herein, the term "size" refers to a characteristic dimension of an object. Thus, for example, a size of an object that is spherical can refer to a diameter of the object. In the case of an object that is non-spherical, a size of the non-spherical object can refer to a diameter of a corresponding spherical object, where the corresponding spherical object exhibits or has a particular set of derivable or measurable characteristics that are substantially the same as those of the non-spherical object. Thus, for example, the size of a non-spherical object can refer to a diameter of a corresponding spherical object that exhibits light scattering characteristics that are substantially the same as those of the non-spherical object. Alternatively, or in conjunction, the size of a non-spherical object can refer to an average of various orthogonal dimensions of the object. Thus, for example, the size of an object that is a spheroidal can refer to an average of a major axis and a minor axis of the object. When referring to a set of objects as having a particular size, it is contemplated that the objects can have a distribution of sizes around the particular size. Thus, as used herein, the size of a set of objects can refer to a typical size of a distribution of sizes, such as an average size, a median size, or a peak size.

[0032] As used herein, the term "nanometer range" or "nm range" refers to a range of dimensions from about 1 nm to about 1 micrometer ("μπι"). The nm range includes the "lower nm range," which refers to a range of dimensions from about 1 nm to about 10 nm, the "middle nm range," which refers to a range of dimensions from about 10 nm to about 100 nm, and the "upper nm range," which refers to a range of dimensions from about 100 nm to about 1 μπι.

[0033] As used herein, the term "micrometer range" or "μπι range" refers to a range of dimensions from about 1 μιη to about 1 millimeter ("mm"). The μπι range includes the "lower μιη range," which refers to a range of dimensions from about 1 μιη to about 10 μηι, the "middle μηι range," which refers to a range of dimensions from about 10 μηι to about 100 μηι, and the "upper μηι range," which refers to a range of dimensions from about 100 μιη to about 1 mm.

[0034] As used herein, the term "aspect ratio" refers to a ratio of a largest dimension or extent of an object and an average of remaining dimensions or extents of the object, where the remaining dimensions are orthogonal with respect to one another and with respect to the largest dimension. In some instances, remaining dimensions of an object can be substantially the same, and an average of the remaining dimensions can substantially correspond to either of the remaining dimensions. For example, an aspect ratio of a spheroid refers to a ratio of a major axis of the spheroid and a minor axis of the spheroid. As used herein, the term "aspect ratio" can refer to one or more of the individual particles present in the compositions of the present invention, for example the nano-sized particles, the micron- sized particles, or both.

[0035] As used herein, the term "nano-sized" refers to an object that has at least one dimension in the nm range. A nano-sized object can have any of a wide variety of shapes, and can be formed of a wide variety of materials.

[0036] As used herein, the term "micron-sized" refers to an object that has at least one dimension in the μηι range. Typically, each dimension of a micron-sized object is in the μηι range or beyond the μη range. A micron-sized object can have any of a wide variety of shapes, and can be formed of a wide variety of materials.

Coating Compositions and Coatings Formed from Coating Compositions

[0037] By way of overview, embodiments of the invention provide a coating composition composed of a base resin and micron-sized and nano-sized pailicles of varying sizes, where the particles are grafted with di-functional or multi-functional organofimctional siloxanes of varying molecular weight (or varying chain lengths) in a dilute organic solvent, and the grafted particles migrate to an outer surface of a resulting coating, it is believed, due to the incompatibility and phase separation between grafted siloxane moieties and hydrocarbon moieties within the base resin. The rapid evaporation of the solvent during the spraying process can also assist in creating the three dimensional hierarchical structure at the surface. The coating composition can be applied as a "one-pot" formulation by, for example, spraying or brushing and cured using a thermally activated catalyst, an UV photocatalyst, or another type of catalyst. Phase separation of the siloxane moieties towards the outer surface is a time- dependent process and can be allowed to occur to a desired extent prior to final curing of the coating composition.

[0038] In various embodiments, a surface of the resulting coating has a three- dimensional hierarchical structure which provides one or more of superhydrophobic, oleophilic or oleophobic (surfaces that repel extremely low-surface-tension liquids, such as various hydrocarbons fluids), self-cleaning, anti-fouling (counteracting or preventing the building up of biological and microbiological deposits on wet surfaces, such as barnacles on the undersides of boats and algae on damp surfaces), anti-icing (the prevention or delay of the formation of ice upon any object) anti-dragging (designed or built to resist the effects of drag in air, land and water vehicles), anti-corrosion, hardness, and abrasion-resistant properties, where the three-dimensional structure is formed by applying a coating composition from a "one-pot" formulation. Once cured, the surface is enriched in grafted particles, including micron-sized and nano-sized particles, providing a three-dimensional roughness along with, or coated in, siloxane that is covalently or hydrogen bonded to both the particles and covalently bonded to a phase-separated base resin within a bulk of the coating (or that is hydrogen bonded to the particles and covalently bonded to the base resin). [0039] The adhesion resistance of the coating to the substrate as measured according to the test methods of ASTM D3359, test method B (i.e. cross hatch test) can be classified as follows:

[0040] ASTM 5B: The edges of the cuts are completely smooth. None of the squares of the lattice is cut.

[0041] ASTM 4B: Small flakes of the coating are detached at intersections. Less than 5% of the area is affected.

[0042] The surface resistance can be 4000 mega ohms or higher as shown in Fig.

16.

[0043] Hydrophobicity recovery of silicone rubber (HTV, RTV and LSR) after exposure to electrical stress (corona or dry-band arcing) is well known. The hydrophobicity of silicone rubbers is due to the low surface energy of the methyl groups orientated to the outer surface. The loss of hydrophobicity of the silicone rubbers is ascribed to the labile surface methyl groups flipping into the depth of the material to a high energy conformation state and also to the introduction of carbonyl and hydroxide groups on the outer surface and in addition evaporation of low molecular weight cyclic and linear siloxanes covering the surface and pollutants on the surface. The hydrophobicity recovery rate (HRR), is influenced by the rate at which the methyl groups flip back to their low energy conformation and the rate of migration of low molecular weight, LMW, oligomers through the bulk and onto the surface. In the case of the nano- and micron particle-filled hydrocarbon siloxane coatings of the present invention, the HRR may also be attributed to the migration of some unbonded organofunctional siloxane oligomers from the bulk onto the outer surface and also the fact that the T_g of the material is higher and thus there is restriction on the ability of the surface methyl groups to orient themselves away from the surface.

[0044] A superhydrophobic surface is not necessarily self-cleaning. In addition to the requirements for superhydrophobicity viz. contact angle greater than or equal to 150 degrees, for self-cleaning the contact angle hysteresis (advancing contact angle minus receding contact angle) must be less than or equal to 10 degrees and sliding angle less than 5 degrees. In various embodiments, the superhydrophobic coatings of the present invention are self- cleaning. In other embodiments, the superhydrophobic coatings of the present invention are not self-cleaning.

[0045] In some embodiments, a three-dimensional structure is formed by grafting functionalized siloxanes onto nano-sized and micron-sized particles, such as nano-sized and micron-sized silica and metal oxide particles, where the siloxanes phase separate from a base resin including hydrocarbon moieties to carry the nano-sized and micron-sized particles adjacent to an outer surface to form a three-dimensional structured surface. Without being bound by any particular mechanism, it is believed that these siloxane-grafted particles migrate to the surface of a coating composition, due to the incompatibility of the siloxanes and the hydrocarbon moieties, which phase-separate to move the siloxane-grafted particles towards the surface of the coating composition.

[0046] In some embodiments, the chain length of a siloxane grafted onto a particle determines the degree of phase separation relative to an outer surface of a coating. Longer siloxane chains can phase-separate to a greater extent and move grafted particles to or near the surface, and shorter siloxane chains can phase-separate to a lesser extent and retain grafted particles closer to a base resin within the bulk of the coating. In some embodiments, longer siloxane chains are grafted onto smaller particles, such as nano-sized particles, and shorter siloxane chains are grafted onto larger particles, such as micron-sized particles. Longer siloxane chains grafted onto nano-sized particles can wrap around or otherwise coat micron- sized or other particles adjacent to the surface, and the grafted nano-sized particles can coat those micron-sized particles, thereby forming a three-dimensional hierarchical structure with roughness on both the nanometer scale and the micrometer scale. The result is that the outer surface is a layer of low-surface energy polysiloxane, for example as shown in Fig. 12.

[0047] In some embodiments, siloxane moieties phase separate from the bulk of a base resin and form a siloxane-enriched layer of thickness in the nanometer range or the micrometer range adjacent to an outer surface. Because the siloxane moieties are covalently bonded to the base resin, undesirable migration of the siloxane moieties can be inhibited. In addition, the free volume of the siloxane moieties is reduced, thereby inhibiting rotational vibrations on the Si-0 ether bonds of the backbone that otherwise can result in flipping of methyl groups and reduction or loss of hydrophobicity. A further degradation mechanism for silicone rubber, viz the reduction in molecular weight due to a back-biting reaction which is catalysed by remnants of the platinum curing catalysts is essentially eliminated due to the lack of addition of platinum catalysts for the polymerization of the siloxane-hydrocarbon base resin in the compositions of the present invention.

[0048] In some embodiments, an increase in adhesion of the superhydrophobic coating to the substrate is obtained by slightly increasing the resin to filler ratio with a slight reduction in hydrophobicity as shown in Example 5 or by the addition of adhesion promoters such as silanes or phosphonates as shown in preferred embodiment 10, by mechanically roughening, by exposing the surface to be coated with corona treatment or by applying a base layer of a hydrocarbon or silicone resin, base layer as shown in Examples 6 and 7.

[0049] In some embodiments, an increase in surface roughness is obtained through the appropriate selection of solvents with different flashpoints during application by spray coating. For example a toluene or ethanol solvent is replaced by a mixture of alcohols or a mixture of various aromatic and aliphatic organic solvents as shown in Example 8.

[0050] In particular embodiments, it is advantageous to apply the compositions of the present invention with "environmentally friendly" solvents, particularly alcohols or mixtures of alcohols. Suitable environmentally friendly solvents include methanol, ethanol, and propanol (e.g. iso-propanol). In particular embodiments, environmentally friendly solvents include mixtures of methanol, denatured alcohol (ethanol), isopropanol, and butanol, for example a 1 :1 :1 :1 mixture of methanol, denatured alcohol, isopropanol and butanol (by volume).

[0051] In some embodiments, an increase in hydrophobicity recovery after ageing (e.g. aging caused by exposing the coating to water and/or by exposing the coating to pollutants), is provided by the migration of low molecular weight siloxanes to the outer surface through the addition of a higher ratio of siloxanes and/or applying the superhydrophobic coating material onto a layer of room-temperature or high temperature vulcanizing silicone rubber, which provides a reservoir of low molecular weight siloxanes as indicated in Example 11.

[0052] In some embodiments, the flexibility of the coating is increased through the addition of additional siloxanes which are copolymerized with the base hydrocarbon resin. Such a formulation is suitable for application on aluminium electrical conductors, e.g. for anti- noise and anti-icing applications as indicated in Example 1.

[0053] Referring to the drawings, FIG. 1 is a schematic of a siloxane-enriched surface of a coating in which a siloxane moiety is phase-separated from a hydrocarbon moiety within a bulk of the coating, according to an embodiment of the invention. In this embodiment, amino-functionalized siloxanes are reacted with epoxide groups of a base cycloaliphatic epoxy resin with a mixture of di- and tri-functional epoxides. As illustrated in FIG. 1, methyl groups of the siloxane moiety are directed towards the open surface, as the lowest energy conformation of the siloxane moiety and imparting hydrophobic properties to the open surface. The free volume of the siloxane moiety is reduced and correspondingly the glass transition temperature is increased, since the siloxane moiety is copolymerized with the base resin.

[0054] FIG. 2 is a schematic of an aminofunctional siloxane grafted onto a particle, such as through hydroxyl groups on a surface of the particle, according to an embodiment of the invention. In this embodiment, the particle is a silica or titanium dioxide particle, although other types of micron- and nano-sized particles are contemplated.

[0055] FIG. 3 is a schematic of the cross-sectional view of a 3 -dimensional hierarchical surface with phase-separated siloxane chains adjacent to a surface of the cured coating, where the siloxane chains are grafted onto micron- and nano-sized particles and copolymerized with a base resin through hydrolytically stable Si-C bonds, according to an embodiment of the invention. In this example, particles of varying sizes are used, including a bimodal particle size distribution of nano-sized particles of silica and titania and micron-sized particles of high aspect ratio silica. As illustrated in FIG. 3, longer siloxane chains along with their grafted nano-sized particles wrap around or otherwise coat the micron-sized particles adjacent to the surface, thereby forming a three-dimensional hierarchical structure with both nanometer scale and micrometer scale roughness.

[0056] FIG. 4 is a schematic of the cross-sectional view of a 3 -dimensional hierarchical surface with phase-separated siloxane chains adjacent to a surface of the cured coating, where the siloxane chains are grafted onto micron- and nano-sized particles and copolymerized with a base resin through hydrolytically stable Si-C bonds, according to an embodiment of the invention. In this example, particles of varying sizes are used, including bi-plurality nano-sized particles of silica and titania and micron-sized particles of low aspect ratio alumina silicate.

[0057] FIG. 5 is a schematic of the use of linker moieties such as silanes or phosphonates between particles and di-functional or multi-functional siloxanes, such that grafted particles are covalently bonded to the siloxanes and therefore to a base hydrocarbon resin (for example an epoxy or an acrylic homopolymer or hydrocarbon-siloxane copolymer), according to an embodiment of the invention.

[0058] As described above, coating compositions of some embodiments are prepared using organofunctional siloxanes. Suitable organofunctional siloxanes include organofunctional polydimethylsiloxanes selected from oligomers or polymers of the formula (Α') or (A"):

(A¹)

(A")

[0059] and having from 2 to 2,000 {-Si(CH₃)₂-0-} units or from 5 to 2,000 {- Si(CH₃)₂-0-} units, and in which Y is a reactive substituent.

[0060] In some embodiments, the organofunctional polydimethylsiloxane (Α') or (A") can have an associated molecular weight from about 116 gnnol^"1 to about 35,000 g^omol^"1, such as from about 900 gTnol^"1 to about 11,000 g'mol^"1. In the case of the organofunctional polydimethylsiloxane (Α'), m can be in the range of 2 to 1,000, such as from 2 to 900, from 2 to 800, from 2 to 700, from 2 to 600, from 2 to 500, from 2 to 400, from 2 to 300, from 2 to 200, from 2 to 100, from 100 to 200, from 100 to 300, from 2 to 50, from 50 to 150, from 50 to 200, from 50 to 300, or a combination thereof. As described above, organofunctional siloxanes of varying molecular weight (or varying chain lengths) can be desirable, and, in the case of the organofunctional polydimethylsiloxane (Α'), a combination or a mixture of such organofunctional polydimethylsiloxanes (Α') with different values of m can be used together, such as shorter siloxane chains with m in the range of 2 to 50 or 2 to 100, and longer siloxane chains with m in the range of 50 to 150, 50 to 200, 50 to 300, 100 to 200, or 100 to 300. Stated in another way, a distribution of chain lengths of such organofunctional polydimethylsiloxanes (Α') can be multi-modal to impart varying extents of phase separation. In the case of the organofunctional polydimethylsiloxane (A"), n can be in the range of 2 to 1,000, such as from 2 to 900, from 2 to 800, from 2 to 700, from 2 to 600, from 2 to 500, from 2 to 400, from 2 to 300, from 2 to 200, from 2 to 100, from 100 to 200, from 100 to 300, from 2 to 50, from 50 to 150, from 50 to 200, from 50 to 300, or a combination thereof. As described above, organofunctional siloxanes of varying molecular weight (or varying chain lengths) can be desirable, and, in the case of the organofunctional polydimethylsiloxane (A"), a combination or a mixture of such organofunctional polydimethylsiloxanes (A") with different values of n can be used together, such as shorter siloxane chains with n in the range of 2 to 50 or 2 to 100, and longer siloxane chains with n in the range of 50 to 150, 50 to 200, 50 to 300, 100 to 200, or 100 to 300. Stated in another way, a distribution of chain lengths of such organofunctional polydimethylsiloxanes (A") can be multi-modal to impart varying extents of phase separation. It is also contemplated that a combination or a mixture of the organofunctional polydimethylsiloxanes (Α') and (A") can be used together.

[0061] Although the formulas (Α') and (A") set forth methyl groups, it is contemplated that at least one of the methyl groups can be replaced by another group or substituent, such as one selected from alkyl groups, alkenyl groups, alkynyl groups, aryl groups, iminyl groups, alkoxy groups, alkenoxy groups, alkynoxy groups, aryloxy groups, carboxy groups, alkylcarbonyloxy groups, alkenylcarbonyloxy groups, alkynylcarbonyloxy groups, arylcarbonyloxy groups, alkylthio groups, alkenylthio groups, alkynylthio groups, arylthio groups, cyano groups, N-substituted amino groups, alkylcarbonylamino groups, N- substituted alkylcarbonylamino groups, alkenylcarbonylamino groups, N-substituted alkenyl carbonylamino groups, alkynylcarbonylamino groups, N-substituted alkynylcarbonylamino groups, arylcarbonylamino groups, N-substituted arylcarbonylamino groups, silyl groups, siloxy groups, and the like.

[0062] In some embodiments, the organofunctional polydimethylsiloxane (Α') or (A") can include at least 2 reactive substituents Y, at least one of which can participate in grafting onto a particle, and at least another one of which can participate in covalent bonding with a base resin, or covalently bond to micron- or nano-sized particles (which can be of the same or different composition as described herein. Specifically, the organofunctional polydimethylsiloxane (Α') or (A") can be copolymerized with the base resin through at least one reactive substituent Y and through at least one hydrolytically stable Si-C bond. Such a hydrolytically stable Si-C bond imparts improved durability and weatherability, and inhibits undesirable migration and/or siloxane copolymer degradation that can otherwise result from bond scission. In some embodiments, such Si-C bonds can involve a covalent bond directly between a Si atom within the polydimethylsiloxane moiety and a carbon atom within the reactive substituent Y. In the case of the organofunctional polydimethylsiloxane (Α'), p can be at least 2, at least 3, at least 4, or at least 5, and can be in the range of 2 to 100, such as from 2 to 50, from 2 to 40, from 2 to 30, from 2 to 20, from 3 to 20, from 4 to 20, from 5 to 20, from 2 to 10, from 3 to 10, from 4 to 10, or from 5 to 10. [00631 The reactive substituent Y can be monofunctional, difunctional, trifunctional, or higher order functional, and can be selected from vinyl substituents, hydrogen substituents, alkoxy substituents, aminoalkyl substituents, alkyldiamino substituents, methoxy substituents, epoxy substituents, epoxy-alkoxy substituents, alkyl ester, mercapto substituents, and the like. In some embodiments, the reactive substituent Y includes a reactive end group, which is separated from a Si atom within the polydimethylsiloxane moiety by 2 to 20 methylene units (or by 2 to 20 carbon atoms), such as by 2 to 10 methylene units (or by 2 to 10 carbon atoms), by 2 to 5 methylene units (or by 2 to 5 carbon atoms), or by 3 methylene units (or by 3 carbon atoms). In the case of the organofunctional polydimethylsiloxane (Α'), the side-substituted Y's can be the same or different. In the case of the organofunctional polydimethylsiloxane (A"), the terminal-substituted Y's are typically the same, although the terminal-substituted Y's also can be different.

[0064] The following sets forth specific examples of the organofunctional polydimethylsiloxane (Α') and A") according to some embodiments.

(1)

[0065] (1) vinyl terminated polydimethylsiloxane, [CAS: 68083-19-2], n = 5 to 480 (or can take on other values set forth above with reference to formula (A")).

(2)

[0066] (2) trimethylsiloxy terminated, vinylmethylsiloxane - dimethylsiloxane copolymer, [CAS: 67762-94-1], m = 10 to 100 and p = 1 to 5 (or can take on other values set forth above with reference to formula (A')).

(3) [0067] (3) trimethylsiloxy terminated, methylhydrosiloxane - dimethylsiloxane copolymer, [CAS: 68037-59-2], m and p can take on values set forth above with reference to formula (Α').

(4)

[0068] (4) α,ψ-aminopropyl terminated polydimethylsiloxane, [CAS: 106214-84- 0], n = 10 to 2000 (or can take on other values set forth above with reference to formula (A"))-

(5)

[0069] (5) aminopropylmethoxysiloxane - dimethylsiloxane copolymer, m and p can take on values set forth above with reference to formula (Α').

(6)

[0070] (6) epoxypropoxypropyl terminated polydimethylsiloxanes, [CAS: 102782-

97-8], n can take on values set forth above with reference to formula (A").

CH₃ CH₃ CH₃

HO— (CH₂)₃— Si-O-f-Si-O- n Si— (CH₂)₃—OH

CH₃ CH₃ CH₃

(7)

[0071] (7) carbinol (hydroxyl) terminated polydimethylsiloxanes, [CAS: 156327- 07-0], n can take on values set forth above with reference to formula (A").

(8) [0072] (8) methacryloxypropyl terminated polydimethylsiloxanes, [CAS: 58130- 03-3], n can take on values set forth above with reference to formula (A").

(9)

[0073] (9) 3-acryloxy-2-hydroxypropyl terminated polydimethylsiloxanes, [CAS: 128754-61-0], n can take on values set forth above with reference to formula (A").

[0074] As described above, coating compositions of some embodiments are prepared using fillers in the form of nano-sized and micron-sized particles. To allow grafting of organofunctional siloxanes, particles desirably include reactive surface groups that can form covalent or hydrogen bonds with reactive substituents Y of the siloxanes. Bonding between particles and organofunctional siloxanes can occur through linker moieties, such as linker moieties including silane groups to bond with particles and epoxide groups to bond with amine groups of organofunctional siloxanes. FIG. 5 illustrates the use of silanes as linker moieties between particles and di-functional or multi-functional siloxanes, such that grafted particles are covalently bonded to the siloxanes and therefore to a base resin.

[0075] Suitable particle fillers include those with a substantially spheroidal shape and an aspect ratio no greater than about 10, such as from about 1 to about 9, from about 1 to about 8, from about 1 to about 7, from about 1 to about 6, from about 1 to about 5, from about 1 to about 4, from about 1 to about 3, or from about 1 to about 2. Smaller aspect ratio particles can exhibit closer packing, which, in turn, can impart desired surface roughness. However, it is contemplated that elongated particles with aspect ratios greater than about 10 also can be used in some embodiments. Suitable particle fillers include nano-sized and micron-sized particles of silica (or Si0₂), fly-ash, alumina silicate, and metal oxides, such as titania (or Ti0₂), Zr0₂, Zn0₂, A1₂0₃, tantalum oxide, tungsten oxide, hafnium oxide, tin oxide, iron oxide, or a combination thereof. In the case of silica particles, examples include colloidal silica, fumed silica, precipitated silica, silica gel, diatomaceous earth, and silica sols. Other examples of suitable particle fillers include nano-sized and micron-sized particles of carbon, metals, metal alloys, semiconductor materials (whether doped or undoped), electrically conductive polymers, other polymeric particles (such as PTFE / fluorocarbon derivatives or silicone (including silsesquioxanes) or hydrocarbon resins including core-shell particle polymers), or a combination thereof. The use of such conductive particle fillers can be used to produce coatings with improved thermal or electrical conductivity, and can be desirable for applications such as anti-icing on conductors where the coatings can assist in de-icing via the Joule effect. Particle fillers can be included in a coating composition at a loading of about 0 to about 150 weight percent of the composition, such as from about 10 to about 140 weight percent, from about 80 to about 120 weight percent, from about 3 to about 50 weight percent, or from about 3 to about 15 weight percent. The particle fillers can be pre-treated with silanes or can be untreated.

[0076] The preferred number ratio of primary micron-size particles to medium sized nanoparticles to small size nanoparticles is about 1 to 1 million to 1 billion particles.

[0077] A mixture or a combination of particle fillers of different sizes or different size distributions can be desirable to impart roughness on different scales. Stated in another way, the distribution of sizes of particle fillers in the compositions of the present invention can be multi-modal. In some embodiments, the distribution of sizes is at least bi-modal with a combination of nano-sized particles and micron-sized particles, and, in other embodiments, the distribution of sizes is at least tri-modal with a combination of nano-sized particles and micron-sized particles. For example, one set (or one population) of particles can have sizes in the lower nm range (e.g., from about 1 nm to about 10 nm), another set (or another population) of particles can have sizes in the middle nm range or the upper nm range (e.g., from about 50 nm to about 150 nm), and yet another set (or yet another population) of particles can have sizes in the lower μιη range, the middle μηι range, or the upper μη range (e.g., from about 1 μπι to about 50 μπι). As another example, one set (or one population) of particles can have a size (e.g., an average, a median, or a peak size) in the nm range and denoted by d, another set (or another population) of particles can have a size (e.g., an average, a median, or a peak size) denoted by ad, with 10 < a < 100, another set (or another population) of particles can have a size (e.g., an average, a median, or a peak size) denoted by pd, with 100 < β < 1,000, and yet another set (or yet another population) of particles can have a size (e.g., an average, a median, or a peak size) denoted by yd, with 1,000 < γ < 10,000. As described above, longer siloxane chains can be grafted onto smaller particles, and shorter siloxane chains can be grafted onto larger particles. Accordingly, for example, a composition according to the present invention comprising a bimodal distribution of particle sizes would have two populations of particles, for example of particle size distribution "d" and "ad" (or "βά" or "yd"); a composition according to the present invention comprising a tri-modal distribution of particle sizes would have three populations of particles, for example of particle size distribution "d", "ad", and "βά"', respectively, etc. It is recognized that the compositions of the present invention which include multimodal article size distributions can include any permutation of different particle sizes as described herein.

[0078] Advantageously, desirable hydrophobic properties of coatings can be achieved using a variety of particle fillers and without requiring the use of hydrophobic particles. Hydrophobic particles can be costly, and are sometimes produced from hydrophilic particles in an extra operation, such as by surface-functionalization reactions. This operation can involve the use of costly reagents, and can give rise to toxic by-products. Inherently hydrophobic materials in bulk form can be converted into a particulate form, albeit involving additional manufacturing cost and time. Through control over phase separation between siloxane moieties and a base resin and through the use of multi-modal, grafted particles to impart surface roughness, desirable hydrophobicity, including superhydrophobicity, can be achieved with hydrophilic particles such as silica and titania particles. However, it is also contemplated that hydrophobic particles can be used in some embodiments, such as polytetrafluoroethylene particles, polyvinylidenefluoride particles, and other polymeric particles that have been surface functionalized with hydrophobic moieties.

[0079] As described above, the coating compositions of some embodiments are prepared using a base resin or a mixture or a combination of different base resins. To allow bonding with grafted siloxanes, a base resin desirably includes reactive groups that can form covalent bonds with reactive substituents Y of the grafted siloxanes. The reactive groups can be monofunctional, difunctional, trifunctional, or higher order functional, and can be selected from vinyl groups, amino groups, diamino groups, epoxide groups, carboxy groups, cyano groups, N-substituted amino groups, and the like. To promote phase separation with grafted siloxanes, a base resin desirably includes hydrocarbon moieties or other types of moieties that are incompatible with or exhibit an aversion towards the siloxanes. Suitable base resins include those that impart desirable properties in a resulting coating, including excellent weatherability or outdoor ageing performance, flexibility, robustness, hardness, strong adhesion to an underlying substrate, and so forth. Suitable base resins include, without limitation, polyacrylates (e.g., polymethylmethacrylates, polymethacrylates, and so forth), cycloaliphatic or other epoxy resins (preferably with a cycloaliphatic anhydride copolymer for improved weatherability and chemical resistance), polyamides, polyesters (e.g., polyethylene terephthalate, polybutylene terephthalate, cyclic butylterepthalate, siliconized polyesters, and so forth), vinyl esters, polyimides, polyphenylene-sulphide, siloxanes, polyolefiiis, polyurethanes, and copolymers thereof.

[0080] In some embodiments, the base resin is desirably a cycloaliphatic resin, or is desirably formed from cycloaliphatic monomers, oligomers, or other prepolymers. A cycloaliphatic resin typically includes non-aromatic ring structures, such as in the form of three-membered rings (e.g., three-rnembered hydrocarbon rings), four-membered rings (e.g., four-membered hydrocarbon rings), five-membered rings (e.g., five-membered hydrocarbon rings), six-membered rings (e.g., six-membered hydrocarbon rings), or higher-membered rings, which can impart excellent weatherability as well as desired mechanical properties including robustness and hardness. Suitable cycloaliphatic resins include cycloaliphatic epoxy resins, such as those formed using cycloaliphatic epoxy prepolymers and anhydride hardeners, amine hardeners, or other types of hardeners. To allow bonding with grafted siloxanes, epoxy resins are desirably epoxide-enriched, such as by including an excess (e.g., by mole, volume, or weight) of an epoxy prepolymer relative to a hardener, so that unreacted epoxide groups remain to form covalent bonds with reactive substituents Y of the grafted siloxanes.

[0081] A mixture or a combination of different base resins can be used to provide a combination of desired properties, such as in the form of a blend or by copolymerization. Copolymerization can be carried out using free-radical curing, thermal curing, UV curing, or a combination thereof. For example, an epoxide-enriched, cycloaliphatic epoxy resin can be reacted with and blended with an organofunctional siloxane or a mixture or a combination of different organofunctional siloxanes, such as the organofunctional polydimethylsiloxane (Α') or (A"), with the siloxane component imparting desired flexibility to a resulting coating, as well as phase separation from the epoxy component for improved hydrophobicity. Flexibility can be desirable for applications where a coating composition is applied to a non-planar substrate or is applied to a planar substrate that is subsequently subjected to rolling operations or other shaping operations. As another example, an epoxy resin (either with or without copolymerization with an organofunctional siloxane) can be blended with a polyacrylate resin (either with or without copolymerization with an organofunctional siloxane), with the polyacrylate component imparting facile curing properties, such as at or near room temperature.

[0082] In some embodiments, the following operations can be involved during preparation of a coating composition: grafting organofunctional siloxanes onto particle fillers, preparing a base resin, combining the grafted particle fillers with the base resin, and optionally adding other fillers and additives. Grafting of the organofunctional siloxane onto the particle fillers can be performed in a dilute solution of the fillers in a solvent whilst stirring or another agitation mechanism. In some embodiments, the particle fillers can be dispersed in the solvent and sonicated before the organofunctional siloxane (or a mixture of organofunctional siloxanes of varying molecular weight) is added whilst stirring. Sonication also can be applied at periodic or non-periodic intervals after addition of the organofunctional siloxane. Preparation of the coating composition can include incoiporating other fillers and additives, such as organic dyes or inorganic pigments, siloxanes as processing aids and to further improve surface hydrophobicity, solid glass particles (or other ceramic particles) that are micron-sized or nano-sized to impart desired surface hardness, flame-retardants (e.g., aluminium tri-hydrate), UV stabilizers (e.g., benzophenones, hindered amine light stabilizers, triazines, and metal-complexed organic molecular deactivators), or a combination thereof.

[0083] Once prepared, a coating composition can be applied on any of a wide variety of substrates (or other structures), including metal substrates, metal alloy substrates (e.g., aluminium-zirconium), ceramic substrates (e.g., glass or porcelain), textiles, concrete structures, polymeric substrates (e.g., a polyester based polymer concrete or a ethylene- propylene or an ethylene-propylene diene rubber or silicone rubber) for coating sub-station shed extenders, and paper, and application of the coating composition can be carried out by conventional coating techniques, including painting, spray coating, roller coating, dip coating, flow coating, and brushing. Substrates can be rigid or flexible, and can be planar or non- planar, such as tubular or other shapes. Once applied, curing of the coating composition to form a coating can be carried out using free-radical curing, thermal curing, UV curing, or a combination thereof, and can be carried out at an elevated temperature, such as from about 100°C to about 300°C, from about 100°C to about 200°C, or from about 150°C to about 200°C, or at a moderate temperature, such as from about 20°C to about 100°C, from about 20°C to about 80°C, or from about 40°C to about 80°C or at ambient temperatures (including sub-zero temperatures in the field). The term "ambient temperature" refers to environmental temperatures experienced when the compositions of the present invention are applied to substrates "in the field". Ambient temperatures range from sub-zero (e.g. about -10°C) to about 40°C. Curing time can be in the range of about 1 min to about 24 hr or more, such as from about 1 min to about 10 hr, from about 1 min to about 5 hr, from about 1 min to about 2 hr, from about 1 hr to about 2 hr, from about 1 min to about 1 hr, from about 1 min to about 50 min, from about 1 min to about 40 min, from about 1 min to about 30 min, from about 1 min to about 20 min, or from about 5 min to about 20 min.

[0084] FIG. 4 and 6 to 14 are microscopy images taken on a scanning electron microscope and light microscope at different focal depths showing surface roughness of a coating implemented in accordance with an embodiment of the invention. As illustrated in FIG. 4 and 6 to 14, the surface is rough on the nanometer scale and the micrometer scale, including micron-sized asperities or textures, with a nearest-neighbor spacing in the micrometer range, such as from about 1 μιη to about 100 μιη, from about 1 μηι to about 50 μηι, from about 15 μηι to about 40 μιτι, from about 15 μιη to about 30 μηι, or from about 15 μηι to about 20 μιη, and which further incorporate or are structured with nano-sized asperities or textures. This hierarchical roughness allows for air gaps such that water does not readily adhere to and wet the surface, such as in accordance with the Lotus effect, and imparts a desired level of hydrophobicity, including superhydrophobicity.

[0085] FIG. 15 is a microscopy image taken on a light microscope at different focal depths at 1 ,200 times magnification showing the homogeneity of the surface roughness of a coating implemented in accordance with an embodiment of the invention. As illustrated in FIG. 15, the surface is rough on the nanometer scale and the micrometer scale, including micron-sized asperities or textures, with a nearest-neighbor spacing in the micrometer range, such as from about 1 μηι to about 100 μπι, from about 1 μπι to about 50 μπι, from about 15 μηι to about 40 μηι, from about 15 μπι to about 30 μηι, or from about 15 μπι to about 20 μπι, and which further incorporate or are structured with nano-sized asperities or textures. This hierarchical roughness allows for air gaps such that water does not readily adhere to and wet the surface, such as in accordance with the Lotus effect, and imparts a desired level of hydrophobicity, including superhydrophobicity.

[0086] The hydrophobicity of a resulting coating can be manifested by a water contact angle that is at least about 45°, such as at least about 60°, at least about 80°, at least about 100°, at least about 120° (the maximum water contact angle that can be achieved with smooth polymers such as fluorocarbons and silicones), or at least about 140°. The superhydrophobicity of a resulting coating can be manifested by a water contact angle that is at least about 150°, such as at least about 155°, at least about 160°, at least about 165°, or at least about 175°. Hydrophobicity, superhydrophobicity, and self-cleaning also can be manifested in a resulting coating in terms of the difference in contact angle between advancing and receding fronts of a moving isolated drop of water, namely hysteresis, with hydrophobicity manifested by a hysteresis that is at least about 10°, and superhydrophobicity and self-cleaning manifested by a hysteresis that is less than about 10° in addition to a sliding angle of less than or equal to 5 degrees. In addition to a desired level of hydrophobicity, a resulting coating can have one or more other desirable properties, such as anti-fouling, anti- icing, anti-dragging, anti-corrosion, electrical noise reduction, hardness, and abrasion-resistant properties.

[0087] Coatings described herein can be incorporated for a wide variety of applications, including: (1) self-cleaning, anti-fouling, and anti-icing coatings for high voltage insulators, conductors, and support structures; (2) self-cleaning, anti-fouling, anti-icing, and anti-corrosion coatings for high voltage conductors, pipes, wind turbines, and steel structui'es; (3) anti-fouling coatings for antennas and biomedical components; (4) anti-corrosion and hydrodynamic drag reduction coatings for boat hulls, land vehicles, and airplanes; and so forth.

Examples

[0088] The following examples describe specific aspects of some embodiments of the invention to illustrate and provide a description for those of ordinary skill in the art. The examples should not be construed as limiting the invention, as the examples merely provide specific methodology useful in understanding and practicing some embodiments of the invention.

Example 1

Materials for Coating Compositions

[0089] The following sets forth characteristics of materials that can be used to prepare certain coating compositions, including coating compositions described in the following examples.

Resin Components

Formula Description Molecular weight Structure

in g/mol

C1 H20O6 Diglycidyl hexahydrophthalate

Diglycidyl 1 ,2-cyclohexanedicarboxylate 284.34

1 ,2-Cyclohexanedicarboxylicacid diglycidylester

equiv/kg = 5.80 - 6.10 0

Epoxy methyl dimethyl Phosphonate

Example 2

Coating Composition

[0090] This example of a coating composition can be generically described as follows. Specifically, the coating composition includes an epoxide-enriched, cycloaliphatic epoxy resin prepared with an anhydride hardener, reacted with and blended with low and medium molecular weight aminofunctioiial siloxanes, and then reacted with sonicated micron- and nano-sized siloxane grafted Si0₂ (4 nm and 20 μηι) and Ti0₂ (80 nm) fillers. The coating composition is spray coated from a toluene solution, and is cured at about 200°C in about 90 minutes.

[0091] The siloxane grafted micron- and nano-sized fillers are first prepared in separate containers. [0092] About 49.1 g of 80 nm titanium dioxide Ti0₂ [CAS: 13463-67-7] is reacted with about 19.6 ml of an alkyl ester polydimethylsiloxane wax in about 98.2 ml of toluene and left to stir at about 50°C on a magnetic stirrer hotplate for about 72 hours in order to graft the siloxane chains onto surfaces of the titanium dioxide particles. The solution is sonicated for about 30 minutes at the start and every 24 hours.

[0093] About 48.21 g of 20 μηι silicon dioxide Si0₂ is reacted with about 19.3 ml of an alkyl ester polydimethylsiloxane wax in about 97 ml of toluene and left to stir at about 50°C on a magnetic stirrer hotplate for about 72 hours in order to graft the siloxane chains onto surfaces of the silica particles. The solution is sonicated for about 30 minutes at the start and every 24 hours.

[0094] About 8.64 g of 4 nm hydrophobic pyrogenic fumed silicon dioxide Si0₂ [CAS: 112945-52-5], with a BET (Brunauer, Emmett, and Teller) surface area of about 120 m².g^"' (silanol group density; SiOH.nm^"2 = 1), is reacted with about 19.3 ml of 3-aminopropyl terminated polydimethylsiloxane [CAS: 97917-34-5], with an amine density of about 0.17 to about 0.22 mmol.g^"1 in which the siloxane moiety included about 130 {-Si(CH₃)₂-0-} units, in about 130 ml of toluene and left to stir at about 50°C on a magnetic stirrer hotplate for about 72 hours in order to graft the siloxane chains onto surfaces of the silica particles. The solution is sonicated for about 30 minutes at the start and every 24 hours.

[0095] The resin is prepared in a separate container. About 10 ml of a cycloaliphatic epoxide mixture of diglycidyl hexahydrophthalate [CAS: 5493-45-8] [MW = 284.34 epoxy equiv. kg^"1 = 5.80 to 6.10] and 3-,4-epoxycyclohexylmethyl-3,4- epoxycyclohexanecarboxylate [CAS: 2386-87-0] [EEW = 131 to 135, MW = 252] is mixed with about 5 ml of 3-aminopropyl terminated polydimethylsiloxane, with an amine density of about 0.62 - 0.74 mmol.g^"1 in which the siloxane moiety included about 36 {-Si(CH₃)₂-0-} units, and about 0.25 ml of another 3-aminopropyl terminated polydimethylsiloxane, with an amine density of about 1.2 to 2.22 mmol.g^"1 in which the siloxane moiety included about 15 {- Si(CH₃)₂-0-} units, in a container with about 10 ml of toluene whilst stirring at room temperature. After about 10 minutes, about 8.5 ml of methyl hexahydrophthalic anhydride [CAS: 25550-51-0] and about 0.5 ml of a tertiary amine catalyst, namely benzyl dimethyl amine or BDMA [CAS: 103-83-3], are added to the stirring solution.

[0096] Dried fillers are added to adjust the viscosity to provide a coating composition that is applied by spray coating. The added fillers are about 14.5 g of 20 μιη silicon dioxide. The mixture of the resin, the grafted fillers, and the ungrafted fillers are then sonicated for about 30 minutes and applied immediately or stored in a freezer.

[0097] A polymer concrete insulator is attached to a drill press using a metal insert and rotated at about 60 rpm. The coating composition is applied using a conventional spray coating equipment. The coating composition is cured in an air-circulating oven at about 200°C for about 120 minutes.

[0098] The static contact angle after curing is typically 170 degrees, the contact angle hysteresis is 2 degrees and the sliding angle is 1 degree but the adhesion is poor.

Example 3

Coating Composition

[0099] This example of a coating composition can be generically described as follows. Specifically, the coating composition includes an epoxide-enriched, cycloaliphatic epoxy-siloxane resin prepared with an anhydride hardener, blended with a polyacrylate- siloxane resin, and then reacted with sonicated micron- and nano-sized siloxane grafted Si0₂ (4 ran and 20 μιη) and Ti0₂ (80 rim) fillers.

[00100] The siloxane grafted micron- and nano-sized fillers are first prepared.

[00101] About 49.1 g of 80 nm titanium dioxide Ti0₂ [CAS: 13463-67-7] is reacted with about 19.6 ml of an alkyl ester polydimethylsiloxane wax in about 146.4 ml of toluene and left to stir at about 50°C on a magnetic stirrer hotplate for about 72 hours in order to graft the siloxane chains onto surfaces of the titanium dioxide particles. The solution is sonicated for about 30 minutes at the start and every 24 hours.

[00102] About 48.21 g of 20 μηι silicon dioxide Si0₂ is reacted with about 19.3 ml of an alkyl ester polydimethylsiloxane wax in about 48.22 ml of toluene and left to stir at about 50°C on a magnetic stirrer hotplate for about 72 hours in order to graft the siloxane chains onto surfaces of the silica particles. The solution is sonicated for about 30 minutes at the start and every 24 hours.

[00103] About 8.64 g of 4 nm hydrophobic pyrogenic fumed silicon dioxide Si0₂ [CAS: 112945-52-5], with a BET (Brunauer, Emrnett, and Teller) surface area of about 120 m².g^_1 (silanol group density; SiOH.nm^"2 = 1), is reacted with about 19.3 ml of 3-aminopropyl terminated polydimethylsiloxane [CAS: 97917-34-5], with an amine density of about 0.17 to about 0.22 mmol.g^"1 in which the siloxane moiety included about 130 {-Si(CH₃)₂-0-} units, in about 130 ml of toluene and left to stir at about 50°C on a magnetic stirrer hotplate for about 72 hours in order to graft the siloxane chains onto surfaces of the silica particles. The solution is sonicated for about 30 minutes at the start and every 24 hours.

[00104] The resins are prepared in separate containers. Two hydrocarbon-based resins are prepared separately, namely an epoxy-siloxane copolymer and a polyacrylate- siloxane copolymer.

[00105] For the epoxy-siloxane copolymer, about 5 ml of a cycloaliphatic epoxide mixture of diglycidyl hexahydrophthalate [CAS: 5493-45-8] [MW = 284.34 epoxy equiv. kg^{" 1} = 5.80 to 6.10] and 3-,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate [CAS: 2386-87-0] [EEW = 131 to 135, MW - 252] is mixed with about 2.5 ml of 3-aminopropyl terminated polydimethylsiloxane, with an amine density of about 0.62 - 0.74 mmol.g^"1 in which the siloxane moiety included about 36 {-Si(CH₃)₂-0-} units, and about 0.125 ml of another 3-aminopropyl terminated polydimethylsiloxane, with an amine density of about 1.2 to 2.22 mmol.g^"1 in which the siloxane moiety included about 15 {-Si(CH₃)₂-0-} units, in a container with about 5 ml of toluene whilst stirring at room temperature. After about 10 minutes, about 4.25 ml of methyl hexahydrophthalic anhydride [CAS: 25550-51-0] and about 0.25 ml of a tertiary amine catalyst, namely benzyl dimethyl amine or BDMA [CAS: 103-83- 3], are added to the stirring solution. Dried fillers are added to adjust the viscosity. The added fillers are about 7.25 g of 20 μιη silicon dioxide.

[00106] For the polyacrylate-siloxane copolymer, about 7.84 g of a polyacrylate is mixed with about 2.5 g of a siloxane with about 150 {-Si(CH₃)₂-0-} units, along with a mixture of solvents, namely about 5.7 ml of propanol, about 5.7 ml of methanol, about 7.5 ml of toluene, and about 1.5 ml of acetone.

[00107] The resins and the grafted fillers are all added together after at least about 72 hours (but less than 10 days). A free-radical generating catalyst is added at about 2% by weight of the polyacrylate resin, namely about 0.16 g of azo-isobutyronitrile or AIBN. The mixture is sonicated for about 30 minutes, and applied immediately or stored in a freezer. Example 4

Coating Composition

[00108] The coating composition of Example 2 is modified by including a cationic photocatalyst in place of BDMA, and is cured by exposure to UV radiation at or near room temperature. Alternatively, it can be cured by using a low temperature activated free radical catalyst, such as AIBN.

[00109] A practitioner of ordinary skill in the art should require no additional explanation in developing the embodiments described herein, but may nevertheless find some useful guidance by examining International Publication No. WO 2009/073901, published on June 11, 2009, the disclosure of which is incorporated herein by reference in its entirety for all purposes.

[00110] While the invention has been described with reference to the specific embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention as defined by the appended claims. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, method, or process to the objective, spirit and scope of the invention. All such modifications are intended to be within the scope of the claims appended hereto. In particular, while the methods disclosed herein have been described with reference to particular operations performed in a particular order, it will be understood that these operations may be combined, sub-divided, or re-ordered to form an equivalent method without departing from the teachings of the invention. Accordingly, unless specifically indicated herein, the order and grouping of the operations are not limitations of the invention.

Example 5

Coating Composition (D65)

[00111] This example of a single layer, high adhesion coating composition can be generically described as follows. Specifically, the coating composition includes an epoxide- enriched, cycloaliphatic epoxy resin prepared with an anhydride hardener, and then reacted with sonicated micron-sized alumina-silicate (10 μιη), and nano-sized siloxane grafted Si0₂ (10 nm) and Ti0₂ (21 nm) fillers. The coating composition is spray coated from an ethanol solution, and is cured at about 200°C in about 120 minutes.

[00112] The siloxane grafted micron- and nano-sized fillers are first prepared in a single container.

[00113] About 5.01 g of 21 nm titanium dioxide Ti0₂ [CAS: 13463-67-7] and 5.00 g of 10 μπι alumino-silicate classified flyash and about 0.924 g of 4 nm hydrophobic pyrogenic fumed silicon dioxide Si0₂ [CAS: 112945-52-5], with a BET (Brunauer, Emmett, and Teller) surface area of about 120 m .g^" (silanol group density; SiOH.nm^" = 1), is reacted with about 5.789 ml of an alkyl ester polydimethylsiloxane wax and about 13.994 ml of 3- aminopropyl terminated polydimethylsiloxane [CAS: 97917-34-5], with an amine density of about 0.17 to about 0.22 mmol.g^"1 in which the siloxane moiety included about 130 {- Si(CH₃)₂-0-} units in about 78.195 ml of ethanol.

[00114] About 8.086 ml of a cycloaliphatic epoxide mixture of diglycidyl hexahydrophthalate [CAS: 5493-45-8] [MW = 284.34 epoxy equiv. kg^"1 = 5.80 to 6.10] and 3- ,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate [CAS: 2386-87-0] [EEW = 131 to 135, MW = 252] is mixed with about 6.892 ml of methyl hexahydrophthalic anhydride [CAS: 25550-51-0] and about 0.5 ml of a tertiary amine catalyst, namely benzyl dimethyl amine or BDMA [CAS: 103-83-3], are added to the stirring solution.

[00115] The solution is sonicated for 30 minutes and left to stir at room-temperature for 12 hours.

[00116] The coating composition is sonicated again for 30 minutes and applied using a conventional spray coating equipment. The coating composition is cured in an air- circulating oven at about 200°C for about 120 minutes.

[00117] The static contact angle after curing is typically 155 degrees, the contact angle hysteresis is 9 degrees and the sliding angle is 4.5 degrees.

Example 6

Coating Composition (D39)

[00118] This is an example of a high-temperature curing double-layer, excellent adhesion coating composition which can be generically described as follows. Specifically, the coating composition for the base layer includes an epoxide-enriched, cycloaliphatic epoxy resin prepared with an anhydride hardener and highly filled with flyash. The outer layer consists of particles such as micron-sized alumina-silicate (10 μιη), and nano-sized siloxane grafted Si0₂ (10 nm) and Ti0₂ (21 nm) fillers treated with a medium molecular weight alkoxy siloxane and a high molecular weight aminofunctional siloxane. The base layer is cured at about 150°C in about 60 minutes and the outer coating is cured at about 200°C in about 120 minutes.

[00119] The base coating is first prepared and applied by spray or brush coating to the substrate such as a ceramic cap-and pin insulator or an aluminium conductor.

[00120] About 10.0 ml of a cycloaliphatic epoxide mixture of diglycidyl hexahydrophthalate [CAS: 5493-45-8] [MW = 284.34 epoxy equiv. kg^"1 = 5.80 to 6.10] and 3- ,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate [CAS: 2386-87-0] [EEW = 131 to 135, MW = 252] is mixed with about 8.5 ml of methyl hexahydrophthalic anhydride [CAS: 25550-51-0] and about 29 g of alumino-silicate, classified flyash in about 10 ml ethanol. About 0.05 ml of a tertiary amine catalyst, namely benzyl dimethyl amine or BDMA [CAS: 103-83-3], are added to the stirring solution.

[00121] The base layer is cured at about 150°C in about 60 minutes.

[00122] The outer surface coating which does not contain any hydrocarbon resin, is then prepared. About 49,088 g of 21 nm titanium dioxide Ti0₂ [CAS: 13463-67-7] and 48.21 g of 20 μηι high aspect ratio silica, and about 8.64 g of 10 nm hydrophobic pyrogenic fumed silicon dioxide Si0₂ [CAS: 112945-52-5], with a BET (Brunauer, Emmett, and Teller) surface area of about 120 m².g^_1 (silanol group density; SiOH.nm^"2 = 1), is reacted with about 67.506 ml of an alkyl ester polydimethylsiloxane wax and about 19.29 ml of 3-aminopropyl terminated polydimethylsiloxane [CAS: 97917-34-5], with an amine density of about 0.17 to about 0.22 mmol.g^"1 in which the siloxane moiety included about 130 {-Si(CH₃)₂-0-} units in about 324.2 ml of ethanol.

[00123] The solution is sonicated for 30 minutes and left to stir at room-temperature for 12 hours.

[00124] The coating composition is sonicated again for 30 minutes and applied using a conventional spray coating equipment. The double-layer coating composition is cured in an air-circulating oven at about 200°C for about 120 minutes.

[00125] The static contact angle after curing is typically 165 degrees, the contact angle hysteresis is unmeasurable (about zero) and the sliding angle is 2 degrees. The adhesion is excellent. Example 7

Coating Composition (El 4)

[00126] This is an example of a low-temperature curing double-layer, excellent adhesion coating composition which can be generically described as follows. Specifically, the coating composition for the base layer includes an unfilled acrylate-urethane resin. The outer surface layer consists of particles such as micron-sized silica (20 μπι), and nano-sized siloxane grafted Si0₂ (10 nm) and Ti0₂ (21 nm) fillers treated with a medium molecular weight alkoxy siloxane and a high molecular weight aminofunctional siloxane. The coating is cured at room- temperature after 24 hours.

[00127] The base coating is first prepared and applied outdoors by spray or brush coating to the substrate such as a sub-station post-insulator or a pylon metal structure.

[00128] An acrylic (BASF Salcomix, Clearcoat, Part A) is mixed with a urethane (BASF Clearcoat Part B). The resin is pre-catalysed.

[00129] The base layer is tack-free at about 25°C after 2 hours and cured in about 12 hours.

[00130] The surface coating which contains acrylic resin and micron- and nano- sized particles, treated with organofunctional siloxanes is then prepared. About 49,088 g of 21 nm titanium dioxide Ti0₂ [CAS: 13463-67-7] and 48.21 g of 20 μηι high aspect ratio silica, and about 8.64 g of 10 nm hydrophobic pyrogenic fumed silicon dioxide Si0₂ [CAS: 1 12945-52-5], with a BET (Brunauer, Emmett, and Teller) surface area of about 120 m².g^_1 (silanol group density; SiOH.nm^" = 1), is reacted with about 67.506 ml of an alkyl ester polydimethylsiloxane wax and about 19.29 ml of 3-aminopropyl terminated polydimethylsiloxane [CAS: 97917-34-5], with an amine density of about 0.17 to about 0.22 mmol.g^"1 in which the siloxane moiety included about 130 {-Si(CH₃)₂-0-} units in about 324.2 ml of ethanol.

[00131] About 10.0 ml of an acrylic (BASF Salcomix, Clearcoat, Part A) is mixed with 5 ml urethane (BASF Clearcoat Part B). The resin is pre-catalysed.

[00132] The solution is sonicated for 30 minutes and left to stir at room-temperature for 12 hours.

[00133] The coating composition is sonicated again for 30 minutes and applied using a conventional spray coating equipment. The double-layer coating composition is cured at room-temperature after about 24 hours. [00134] The static contact angle after curing is typically 160 degrees, the contact angle hysteresis is 8 and the sliding angle is 4 degrees.

Example 8

Coating Composition (Mixed Solvent)

[00135] These formulations refer to any of the above preferred embodiments where the solvent (ethanol) or toluene is replaced by a mixed solvent with numerous components with varying flash points and boiling points such as BASF Salcomix SV 13-0732-0101.

Example 9

Coating Composition

[00136] These formulations refer to any of the above preferred embodiments where the primary micron size particle is replaced by a naturally occurring mineral / substance with inherent surface texture on the 10 to 50 micron-sized particles is in the range of 1 to 5 microns for example Idwala Pyrofil alumino-silicate mined in South Africa as shown in Fig. 14.

Example 10

Coating Composition (bonding agents)

[00137] These formulations refer to any of the above preferred embodiments where the coating is applied to a surface treated with bonding agents such as silanes and or phosphonates. In addition the use of boding agents as covalent linkers between the micron- and nano-sized particles and the siloxanes is included. The concept is illustrated in the graphic in Fig. 5.

Example 11

Coating Composition (RTV base coating)

[00138] These room-temperature curing formulations are similar to preferred embodiment 7 but the base layer acrylic is replaced by a room-temperature vulcanizing, RTV, silicone rubber. This base layer provides a reservoir of low molecular weight siloxanes and also provides a thicker coating which is more aesthetically pleasing.

Example 12

Coating Composition (Rapid ultra-high temperature cure)

[00139] The coatings in this embodiment include the high temperature curing coatings such as those with a siloxane-epoxy base which can be cured within 5 minutes using ultra-high temperatures such as 400 degrees Celsius and may find application in the field in terms of coating sub-station insulators (with jacketed infra-red heaters) or coating conductors in sub-zero temperatures using a robotic coating devices travelling down transmission lines.

Claims

What is claimed is:

1 A coating, comprising:

a base resin which is a thermoset or a thermoplastic or both, comprising hydrocarbon moieties;

micron-sized and nano-sized particles; and

a mixture of polysiloxanes comprising multi-functional polysiloxanes of varying molecular weight;

wherein the multi-functional polysiloxanes are copolymerized with the base resin and grafted onto the micron-sized and nano-sized particles, and the grafted particles are disposed at or on the outer surface of the coating, thereby forming a three-dimensional hierarchical structure comprising micron-sized and nano-sized asperities.

2. The coating of claim 1 , wherein the surface of the micron-sized and nano-sized particles is functionalized with reactive surface groups which form covalent or hydrogen bonds with the multi-functional polysiloxanes.

3. The coating of claim 1, wherein the micron-sized and nano-sized particles have at least a tri-modal particle size distribution.

4. The coating of claim 1, wherein the coating is superhydrophobic and self-cleaning.

5. The coating of claim 1, wherein the coating has at least one property selected from the group consisting of superhydrophobic, oleophilic, oleophobic, self-cleaning, anti-fouling, anti-icing, anti-dragging, anti-corrosive, hard, and abrasion-resistant.

6. The coating of claim 1, wherein the base resin comprises a copolymer of a siloxane and a hydrocarbon polymer or oligomer, wherein the hydrocarbon polymer or oligomer is an epoxy resin, a polyurethane resin, a polyacrylate resin, or any combination thereof.

7. The coating of claim 1, wherein the micron-sized and nano-sized particles are electrically conductive, thermally conductive, electrically and thermally conductive, or comprise a non-conductive metal-oxide.

8. A method of forming the coating of claim 1, comprising applying a solution of the coating onto a substrate by spraying or brushing.

9. The method of claim 8, wherein the coating is cured at ambient temperature after said applying.

10. The method of claim 8, wherein the solution of the coating of claim 1 further comprises a solvent comprising one or more alcohols.

11. The method of claim 8, wherein the solution of the coating further comprises a mixture of solvents with different flash points.

12. A superhydrophobic coating comprising the composition of claim 1, which exhibits hydrophobicity recovery and/or self-healing after exposure to corona discharge, dry-band arcing or pollution build-up.