Optically Transparent Superhydrophobic Film

Abstract

To provide a coating that can be easy to apply, clear, well-bonded, and superhydrophobic.SOLUTION: In one aspect, a method for coating a substrate comprises: providing a substrate having a surface; and disposing a coating composition adjacently to the surface. The composition comprises: a hydrophobic fluorinated solvent; a binder comprising a hydrophobic fluorinated polymer; and hydrophobic fumed silica nanoparticles. Also disclosed is an article comprising a coating layer, the coating layer comprising a plurality of nanoparticles partially exposed on an outside surface thereof.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 62 / 635,993, filed February 27, 2018, U.S. Patent Application No. 15 / 991,873, filed May 29, 2018, and U.S. Patent Application No. 16 / 286,545, filed February 26, 2019, the entire contents of each of which are incorporated herein by reference. [Background technology]

[0002] Unless otherwise indicated herein, the materials described in this section are not prior art to the claims of this application and are not admitted to be prior art by inclusion in this section.

[0003] Superhydrophobic surfaces and coatings with exceptional water repellency have potential applications in many applications. Well-adhered optically clear coatings have been achieved, as have optically clear superhydrophobic coatings. However, there remains a need for easily applied, optically clear, well-adhered superhydrophobic coatings or thin films. This is because the physical properties that can achieve these three properties tend to be mutually exclusive when using traditional thin film materials and methods. For example, superhydrophobic materials typically have micrometer to nanometer surface roughness, which tends to scatter light and makes optical transparency difficult to achieve. Similarly, materials with high optical transparency tend to have low surface roughness (i.e., very smooth surfaces) and typically cannot adhere well to low surface energy hydrophobic materials. Additionally, there remains a need for superhydrophobic coatings that can retain their hydrophobicity even after extensive wear. Summary of the Invention

[0004] In one aspect, the present disclosure provides a method for coating a substrate comprising: providing a substrate having a surface; disposing a coating composition adjacent to the surface, the composition comprising a hydrophobic fluorinated solvent, a binder comprising a hydrophobic fluorinated polymer, and silica nanoparticles; and evaporating the fluorinated solvent.

[0005] In another aspect, the present disclosure includes an article comprising a coating layer, the coating layer having an inner surface and an opposing outer surface, the inner surface disposed adjacent to a substrate surface, the coating layer comprising a hydrophobic fluorinated polymer and a plurality of nanoparticles, at least a portion of the nanoparticles being partially exposed on the outer surface of the coating layer.

[0006] These and other aspects, advantages, and alternatives will become apparent to those skilled in the art from a reading of the following detailed description, with appropriate reference to the accompanying drawings. [Brief description of the drawings]

[0007] [Figure 1] 1 shows a diagram of an exemplary superhydrophobic optical thin film including various thin film layers and associated hydrophobic nanoparticles, according to an aspect of the present disclosure. [Diagram 2] 1 shows a diagram of an exemplary superhydrophobic optical thin film including various thin film layers, associated hydrophobic nanoparticles, and depressions from displaced nanoparticles, according to an embodiment of the present disclosure. [Diagram 3] 1 shows a flowchart illustrating a method according to an example embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The following detailed description describes various features and functions of the disclosed methods, compositions, and structures. The illustrative embodiments described herein are not meant to be limiting. It will be readily understood that certain aspects of the disclosed methods, compositions, and structures can be arranged and combined in a wide variety of different configurations, all of which are contemplated herein.

[0009] Described herein are superhydrophobic compositions that are easily applied and well-adhered without sacrificing hydrophobicity or light transmission. As used herein, "superhydrophobic" describes a surface or coating that has a water contact angle of at least about 130°. Also, as used herein, a "light-transmitting" coating transmits at least about 90% of incident light having a wavelength within the range of 300 nm to 1500 nm. As used herein, "well-adhered" refers to a composition that, when applied to a substrate as a coating or thin film, adheres to the substrate such that it is not easily removed by a relatively small amount of shear force (e.g., friction) or exposure to environmental conditions (e.g., sun, rain, wind, etc.).

[0010] In one aspect, the present disclosure provides a method for producing a method for manufacturing a semiconductor device comprising: a hydrophobic fluorinated solvent; a binder comprising a hydrophobic fluorinated polymer; hydrophobic fumed silica nanoparticles; and optionally hydrophobic aerogel nanoparticles.

[0011] The hydrophobic fluorinated solvent may be a fluorinated material capable of dissolving the binder described herein. To provide good optical clarity of the resulting film or coating, it is beneficial for the composition to include well-dispersed particles throughout the deposition process. If the particles are too large or poorly dispersed, the superhydrophobic surface may become cloudy. The desired dispersion may be achieved by using a suitable hydrophobic fluorinated solvent that may act as a dispersant. In some embodiments, the hydrophobic fluorinated solvent may include a fluorinated alkane, a fluorinated trialkylamine, a fluorinated cycloalkane, a fluorinated heterocycloalkane, or a combination thereof. In some embodiments, the fluorinated component may be perfluorinated. Suitable fluorinated solvents are commercially available from a number of sources, such as Sigma Aldrich (St. Louis, MO), 3M (Maplewood, MN). Suitable fluorinated solvents include perfluorooctane, 2H,3H-perfluoropentane, perfluorotributylamine, perfluorodecalin, and perfluorononane, such as, for example, Fluorinert™ FC-40, Fluorinert™ FC-75, Fluorinert™ FC-770, or equivalent or similar materials.

[0012] In some embodiments, the hydrophobic fluorinated solvent may include a crosslinked silane. The crosslinked silane may be selected from crosslinkers known in the art having at least one silicon atom. Suitable crosslinked silanes are commercially available from many sources, such as Sigma Aldrich (St. Louis, MO), 3M (Maplewood, MN). Suitable crosslinked silanes include, for example, silanes having hydride functionality, vinyl functionality, etc., such as Novec™ 2702, Novec™ 2202, Novec™ 1720, or equivalent or similar materials. When a crosslinked silane is included, the amount of binder used in the composition may be reduced to about 0.3% to about 1.0% by weight of the composition.

[0013] The fluorinated polymer binder may include a hydrophobic fluorinated polymer that can be dissolved in the hydrophobic fluorinated solvent described herein. The binder may allow the hydrophobic particles to adhere to the surface of the substrate, but if the binder is not properly selected or used in the wrong amount, the binder may affect the optical transparency of the resulting film or coating. The fluorinated polymer binder is preferably optically transparent and amorphous. In some embodiments, the fluorinated polymer binder may be a fluoroalkyl polymer, a fluoroalkoxy polymer, a perfluoroalkyl polymer, a perfluoroalkoxy polymer, or a combination thereof. Suitable fluorinated polymer binders are commercially available from a number of sources, such as Solvay (Brussels, Belgium). Suitable fluorinated polymer binders may include, for example, Teflon® AF and Hyflon® AD.

[0014] The amount of binder in the composition is related to the ability of the composition to form a film or coating with the desired superhydrophobic, optically transparent, and well-adhered properties described herein. If too much binder is used in the composition, the nanoparticles may be encapsulated by the binder to such an extent that the surface loses its nanotexturing and therefore its superhydrophobic properties. If too little binder is used, the nanoparticles may not be effectively adhered to the substrate and adhesion to the substrate may be affected. In some embodiments, the fluorinated polymer binder is present at about 0.3% to about 1.5% by weight of the composition. In other embodiments, the binder is present at about 0.8% to about 1.2% by weight of the composition. The binder may also be present at about 0.3% to about 1.4%, about 0.4% to about 1.5%, about 0.3% to about 1.3%, about 0.4% to about 1.3%, about 0.4% to about 1.2%, about 0.5% to about 1.2%, about 0.5% to about 1.1%, about 0.5% to about 1.0%, about 0.6% to about 1.0%, about 0.7% to about 1.4%, about 0.5% to about 1.5%, about 0.5% to about 1.2%, or about 0.3% to about 0.9% by weight of the composition.

[0015] A wide variety of fumed silica materials are known in the art, including, for example, fumed silica with various particle size distributions or average particle sizes, or flat surface-treated fumed silica. In certain embodiments described elsewhere herein, the fumed silica nanoparticles are high surface area, nanostructured, and / or nanoporous particles with an average particle size of about 200 nm or less. The average fumed silica nanoparticle size may represent the average linear dimension of the particles (e.g., in the case of substantially spherical particles, the average diameter), the average granulation or crystallite size, or in the case of aggregated particles, the average aggregate size. In some embodiments, the average fumed silica nanoparticle size may be less than about 100 nm, less than about 75 nm, or less than about 50 nm. However, excessively small fumed silica nanoparticles (e.g., a few nanometers or less) may be difficult to disperse. In some embodiments, the average fumed silica nanoparticle size is about 10 nm to about 200 nm, about 25 nm to about 100 nm, or about 40 nm to about 60 nm.

[0016] The hydrophobic fumed silica nanoparticles may be silica nanoparticles chemically modified with hydrophobic silanes. In some embodiments, the nanoparticles are chemically treated with fluorinated materials. In other embodiments, the nanoparticles are chemically treated with polydimethylsiloxane (PDMS). Colloidal silicon dioxide made from fumed silica is prepared by a suitable process to reduce particle size and modify surface properties. The surface properties are modified to produce fumed silica by producing silica materials under conditions of gas-phase hydrolysis at elevated temperatures with surface-modifying silicon compounds (e.g., silicon dimethyl bichloride). The hydrophobicity of the fumed silica nanoparticles is the result of treatment with at least one compound selected from the group consisting of organosilanes, fluorinated silanes, and disilazanes.

[0017] Suitable organosilanes include alkylchlorosilanes, alkoxysilanes, such as methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, i-propyltrimethoxysilane, i-propyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, n-octyltriethoxysilane, phenyltriethoxysilane, and polytriethoxysilane. Examples of suitable alkyl silanes include, but are not limited to, oxysilanes, trialkoxyarylsilanes, isooctyltrimethoxy-silane, N-(3-triethoxysilylpropyl)methoxyethoxyethoxyethyl carbamate, N-(3-triethoxysilylpropyl)methoxyethoxyethoxyethyl carbamate, polydialkylsiloxanes, including polydimethylsiloxanes, arylsilanes, including substituted and unsubstituted arylsilanes, alkylsilanes, including substituted and unsubstituted alkylsilanes, including methoxy and hydroxy substituted alkylsilanes, and combinations thereof. Suitable alkylchlorosilanes include, for example, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, octylmethyldichlorosilane, octyltrichlorosilane, octadecylmethyldichlorosilane, and octadecyltrichlorosilane. Other suitable materials include, for example, methylmethoxysilanes, such as methyltrimethoxysilane, dimethyldimethoxysilane, and trimethylmethoxysilane; methylethoxysilanes, such as methyltriethoxysilane, dimethyldiethoxysilane, and trimethylethoxysilane; methylacetoxysilanes, such as methyltriacetoxysilane, dimethyldiacetoxysilane, and trimethylacetoxysilane; vinylsilanes, such as vinyltrichlorosilane, vinylmethyldichlorosilane, vinyldimethylchlorosilane, vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, and vinyldimethylethoxysilane.

[0018] Suitable fluorinated silanes include fluorinated alkyl-, alkoxy-, aryl-, and / or alkylaryl-silanes, as well as fully perfluorinated alkyl-, alkoxy-, aryl-, and / or alkylaryl-silanes. An example of a suitable fluorinated alkoxy-silane is perfluorooctyltrimethoxysilane.

[0019] Suitable disilazanes include, for example, hexamethyldisilazane, divinyltetramethyldisilazane, and bis(3,3-trifluoropropyl)tetramethyldisilazane. Cyclosilazanes are also suitable and include, for example, octamethylcyclotetrasilazane.

[0020] Suitable hydrophobic fumed silica nanoparticles are commercially available from a number of sources, including Cabot Corporation (Tuscola, Ill.) under the trade name CAB-O-SIL, and Degussa, Inc. (Piscataway, N.J.) under the trade name AEROSIL. Suitable hydrophobic fumed silica particles include, for example, AEROSIL[R]R202, AEROSIL[R]R805, AEROSIL[R]R812, AEROSIL[R]R812S, AEROSIL[R]R972, AEROSIL[R]R974, AEROSIL[R]R8200, AEROXIDE[R]LE-1, and AEROXIDE[R]LE-2.

[0021] In some embodiments, the hydrophobic fumed silica nanoparticles are present at about 0.01% to about 0.5% by weight of the composition, while in other embodiments, the hydrophobic fumed silica nanoparticles are present at about 0.08% to about 0.12% by weight of the composition. The hydrophobic fumed silica nanoparticles may be present at about 0.03% to about 0.5% by weight, about 0.04% to about 0.5% by weight, about 0.03% to about 0.4% by weight, about 0.04% to about 0.4% by weight, about 0.04% to about 0.3% by weight, about 0.05% to about 0.2% by weight, about 0.05% to about 0.1% by weight, about 0.05% to about 0.1% by weight, about 0.06% to about 0.1% by weight, about 0.07% to about 0.1% by weight, about 0.05% to about 0.5% by weight, about 0.05% to about 0.3% by weight, or even about 0.01% to about 0.09% by weight of the composition.

[0022] In some embodiments, the composition may further include hydrophobic aerogel nanoparticles. Combining hydrophobic fumed silica nanoparticles with hydrophobic aerogel nanoparticles may provide additional water repellency to the coating or film. Superhydrophobic coatings that include hydrophobic aerogel nanoparticles but no fumed silica nanoparticles may provide superhydrophobic, optically transparent thin films. However, these films collapse with small amounts of shear force. Thus, such coatings are easily destroyed by friction and do not provide lasting protection to the coated surface. However, compositions that include hydrophobic fumed silica nanoparticles provide more durable superhydrophobic coatings that can adhere well to glass surfaces. Combining hydrophobic aerogel with hydrophobic fumed silica allows the aerogel to be protected from frictional shear forces by "hiding" between the well-adhered fumed silica nanoparticles (see FIG. 1). The addition of hydrophobic aerogel nanoparticles may further enhance the superhydrophobic behavior of the film while maintaining good durability.

[0023] Suitable hydrophobic aerogel nanoparticles have a density of approximately 100-200 kg / m 3The density and average particle size of the particles are approximately 200 nm or less, and the surface area is very high (600-800 m 2 / g) of particles. The average aerogel nanoparticle size refers to the average linear dimension of the particles (e.g., in the case of substantially spherical particles, the average diameter) and may refer to the average grain size or crystallite size, or in the case of aggregated particles, the average aggregate size. In some embodiments, the average aerogel nanoparticle size may be less than about 100 nm, less than about 75 nm, or less than about 50 nm. However, excessively small aerogel nanoparticles (e.g., a few nanometers or less) may be difficult to disperse. In some embodiments, the average aerogel nanoparticle size is about 10 nm to about 200 nm, about 25 nm to about 100 nm, or about 40 nm to about 60 nm.

[0024] Hydrophobic aerogel nanoparticles can be obtained from precursor powders that have been processed to reduce the average particle size to about 200 nm or less. Hydrophobic aerogel nanoparticles can include nanoscale surface textures that feature protruding or sharp features separated by recessed features and / or pores on the particle surface. Coating compositions that include particles with such nanoscale surface textures can result in coatings with higher water contact angles, thus improving hydrophobicity. As one skilled in the art will recognize, the scale of the surface texture is smaller than the average particle size, and generally the surface texture is at least about 50% smaller. For example, aerogel particles with an average particle size of about 100 nm can include surface textures with an average size of about 25 nm or less, and hydrophobic particles with an average particle size of about 50 nm can include surface textures with an average size of about 25 nm or less.

[0025] Suitable aerogel precursor powders are commercially available from a number of sources, including Cabot Corp. (Boston, Massachusetts). Suitable aerogel precursor powders are sold under the trade names Nanogel® Aerogel, LUMIRA® Aerogel, and ENOVA® Aerogel, including, for example, ENOVA™ Aerogel IC3110, ENOVA™ Aerogel MT1100, ENOVA™ Aerogel MT1200, ENOVA™ Aerogel IC3120. These porous nanostructured particles are available in particle sizes ranging from about 5 micrometers to 4 mm, but may be mechanically milled or sonicated as described below to obtain particles of smaller size (e.g., less than about 50 nm) for use in forming superhydrophobic coatings.

[0026] In another aspect, the present disclosure provides a method for making the compositions described herein, the method comprising: (a) combining a hydrophobic fluorinated solvent, a binder comprising a hydrophobic fluorinated polymer, fumed silica nanoparticles, and optionally, hydrophobic aerogel nanoparticles; (b) mixing the combinations; and (c) drying the mixture to provide the composition.

[0027] In embodiments in which the composition includes hydrophobic aerogel nanoparticles, the combination may further include hydrophobic aerogel nanoparticles added prior to mixing. Mixing by sonication (e.g., by an ultrasonic probe) can be used to break up agglomerates of the hydrophobic fumed silica nanoparticles and / or hydrophobic aerogel nanoparticles, for example, when the agglomerated nanoparticles are large enough to scatter a significant amount of light.

[0028] Advantageously, the inventors have determined that such compositions can be easily applied to a substrate to provide a well-adhered, optically clear, hydrophobic coating. Accordingly, another aspect of the disclosure is a method for coating a substrate. An exemplary method 300 for coating a substrate is shown in FIG. 3. The method 300 may include, at block 302, providing a substrate having a surface, and, at block 304, disposing a coating composition adjacent to the surface. In certain embodiments, the method 300 may include treating the substrate at block 308 prior to disposing the coating composition at block 304. The composition includes a hydrophobic fluorinated solvent, a binder including a hydrophobic fluorinated polymer, and hydrophobic fumed silica nanoparticles. At block 306, the method may further include evaporating the fluorinated solvent.

[0029] The amounts and identities of the various components can be as described elsewhere above with respect to the compositions of the present disclosure. For example, in certain embodiments described elsewhere herein, the coating composition further comprises hydrophobic aerogel nanoparticles.

[0030] Thus, in certain embodiments described elsewhere herein, the binder is present in the coating composition in an amount ranging from 0.3% to 1.5% by weight. For example, in certain such embodiments, the binder is present in an amount ranging from 0.5% to 1.5% by weight, or from 0.8% to 1.5% by weight, or from 0.3% to 1.2% by weight, or from 0.8% to 1.2% by weight of the coating composition. In certain embodiments described elsewhere herein, the silica nanoparticles are present in the coating composition in an amount ranging from 0.01% to 0.5% by weight. For example, in certain such embodiments, the silica nanoparticles are present in an amount ranging from 0.03% to 0.5%, or from 0.05% to 0.5%, or from 0.08% to 0.5%, or from 0.01% to 0.4%, or from 0.01% to 0.25%, or from 0.01% to 0.12%, or from 0.03% to 0.4%, or from 0.05% to 0.25%, or from 0.08% to 0.12% by weight of the coating composition. In certain embodiments described elsewhere herein, the aerogel nanoparticles are present in the coating composition in an amount ranging from 0.1% to 0.5% by weight. For example, in certain such embodiments, the aerogel nanoparticles are present in an amount in the range of 0.2% to 0.5% by weight, or 0.3% to 0.5% by weight, or 0.1% to 0.4% by weight, or 0.1% to 0.3% by weight, or 0.15% to 0.45% by weight of the coating composition.

[0031] For example, in certain embodiments described elsewhere herein, the average size of the silica nanoparticles, or the average size of the silica nanoparticles and aerogel nanoparticles, is within the range of 10 nm to 200 nm, or 25 nm to 200 nm, or 50 nm to 200 nm, or 100 nm to 200 nm, or 10 nm to 150 nm, or 10 nm to 100 nm, or 10 nm to 50 nm, or 25 nm to 150 nm, or 50 nm to 100 nm. In some instances, it may be desirable to have the average size of the silica nanoparticles and aerogel nanoparticles equivalent to no more than 10% of the electromagnetic radiation wavelength (i.e., radio waves and / or light) in order to render the particles transparent to electromagnetic radiation.

[0032] In certain embodiments described elsewhere herein, disposing the coating composition includes spraying the composition onto the substrate surface. Advantageously, the inventors have determined that unlike other well-adhered superhydrophobic light-transmitting thin films known in the art, the sprayable compositions described elsewhere herein can be easily handled and applied. While conventional compositions are often applied by complex, expensive, and cumbersome processes such as physical vapor deposition, the compositions described herein may be applied to the substrate by, for example, spray coating, spin coating, dip coating, or other deposition techniques known in the art. Typically, the compositions are deposited on a transparent substrate formed from a light-transmitting material such as glass or acrylic, although other substrates may be used.

[0033] In certain embodiments described elsewhere herein, evaporating the fluorinated solvent includes air drying or heating the substrate and / or deposition composition at a temperature above the boiling point of the fluorinated solvent. For example, when using Fluorinert™ FC-40 (boiling point 165° C.) as the fluorinated solvent, the substrate may be heated to a temperature above 165° C. to facilitate evaporation of the fluorinated solvent.

[0034] As discussed above, a crosslinked silane may be included in the coating composition. In certain such embodiments, the method further includes curing the disposed coating composition. In certain embodiments described elsewhere herein, curing the disposed coating composition includes heating the disposed composition to a temperature sufficient to provide a crosslinked coating. For example, in certain such embodiments, the method includes disposing a coating composition including a crosslinked silane adjacent to a substrate surface and curing the disposed coating composition at a temperature of at least 150° C., or at least 175° C., or at least 200° C. for a time sufficient to provide a crosslinked coating composition. In certain such embodiments, the method includes curing the coating composition for a time in the range of 30 minutes to 90 minutes, or 45 minutes to 90 minutes, or 60 minutes to 90 minutes, or 30 minutes to 75 minutes, or 30 minutes to 60 minutes, or 45 minutes to 75 minutes, for example, in certain embodiments described elsewhere herein, curing the disposed coating composition includes heating the disposed composition to a temperature sufficient to provide a crosslinked coating (e.g., a temperature of at least 150° C.) for about 60 minutes.

[0035] In certain embodiments described elsewhere herein, the method includes treating the substrate (e.g., block 308 of method 300). For example, in certain such embodiments, treating the substrate includes depositing a silane on at least a portion of the substrate surface (i.e., prior to disposing the coating composition). In another example, in certain embodiments described elsewhere herein, treating the substrate includes plasma etching the substrate. In certain such embodiments, plasma etching the substrate generates hydroxyl functional groups on the substrate surface.

[0036] Advantageously, the inventors have determined that treating the substrate surface and / or disposing a coating composition comprising a crosslinked silane can improve adhesion of the coating composition to the substrate (e.g., when the substrate is a highly hydrophilic material such as glass). In certain embodiments described elsewhere herein, the coating composition comprising a crosslinked silane is disposed adjacent to an untreated substrate surface (e.g., a surface lacking significant hydroxyl and / or silane functionality). In other embodiments, the coating composition lacking a crosslinked silane is disposed adjacent to a treated substrate surface (e.g., a plasma etched and / or silane functionalized surface). Of course, in certain embodiments described elsewhere herein, the coating composition comprising a crosslinked silane is disposed adjacent to a treated substrate surface (e.g., a plasma etched surface).

[0037] Another aspect of the present disclosure is a coated substrate prepared by the methods described herein. For example, in certain embodiments, the coated substrate is a structure including a substrate and a superhydrophobic coating on at least a portion of the substrate. When the coating is on the substrate, the resulting film is superhydrophobic, optically transparent, and well-adhered to the substrate. The superhydrophobic coating may have a water contact angle of at least 130°. In certain such embodiments, the superhydrophobic coating has a water contact angle of at least 150°. For example, the water contact angle may be at least 130°, at least 135°, at least 140°, at least 145°, at least 150°, at least 155°, at least 160°, at least 165°, at least 170°, or at least 175°. In some embodiments, the water contact angle encompasses both advancing and receding water contact angles.

[0038] In some embodiments, the superhydrophobic coating may have at least 95% light transmission for wavelengths between 300 nm and 1500 nm, or visible wavelengths between 400 nm and 700 nm. The substrate may also be a light-transmitting material, such as glass or plastic. In embodiments in which the substrate is also light-transmitting, the coated substrate allows light (e.g., from a laser or optical sensor) to pass through the substrate and the superhydrophobic coating with limited interference. The superhydrophobicity of the coating may also allow the substrate to remain clean and dry by limiting the ability of water (e.g., rain) and dirt or dust to accumulate on the surface.

[0039] The superhydrophobic coating may also adhere to the substrate such that it will not be removed by friction or by exposure to environmental conditions (e.g., sun, rain, wind, etc.) This aspect of the superhydrophobic coating allows a single application to remain on a substrate for extended periods of time, a feature previously unknown in superhydrophobic, light-transmitting coatings.

[0040] In some embodiments, the structure further comprises a silane layer disposed between the superhydrophobic coating and the substrate. The silane may be used to modify the surface energy or wettability of the surface of the substrate prior to application of the superhydrophobic composition. The silane may be a silicon-containing compound having a linear alkyl, branched alkyl, or aryl group, including bipodal silanes, and may be optionally fluorinated. In some embodiments, the silane is a hydrophobic silane. Suitable silanes include, for example, organoethoxysilane, trimethoxysilane, (perfluorobutyl)ethyltriethoxysilane, (3,3,3-trifluoropropyl)trimethoxysilane, and any silane described herein. However, if the fluorinated solvent comprises a crosslinked silane, the fluorinated silane layer may not be necessary.

[0041] Another aspect of the present disclosure is an article comprising a coating layer, the coating layer having an inner surface and an opposite outer surface, the inner surface being disposed adjacent to a substrate surface. The coating layer comprises a hydrophobic fluorinated polymer and a plurality of nanoparticles, at least some of the nanoparticles being partially exposed on the outer surface of the coating layer. In certain embodiments, the coating layer is a dried product of a coating composition as described elsewhere herein. Thus, in such embodiments, the amounts and identities of the various components may be as described elsewhere above for the compositions of the present disclosure.

[0042] For example, in certain embodiments described elsewhere herein, the nanoparticles are selected from one or more of silica nanoparticles and aerogel nanoparticles. In certain such embodiments, the average size of the nanoparticles is in the range of 10 nm to 200 nm. For example, in certain embodiments described elsewhere herein, the nanoparticles are selected from one or more of silica nanoparticles and aerogel nanoparticles and have an average size in the range of 10 nm to 200 nm, or 25 nm to 200 nm, or 50 nm to 200 nm, or 100 nm to 200 nm, or 10 nm to 150 nm, or 10 nm to 100 nm, or 10 nm to 50 nm, or 25 nm to 150 nm, or 50 nm to 100 nm.

[0043] In certain embodiments described elsewhere herein, the nanoparticles are relatively uniformly dispersed throughout the coating layer, while in other embodiments, the nanoparticles are localized at the outer surface of the coating layer (e.g., the product of depositing the nanoparticles on the surface of the coating layer).

[0044] In certain embodiments, nanoparticles that are partially exposed on the outer surface of the coating layer can be displaced from the coating layer, e.g., by exposure to weather, to provide corresponding depressions in the outer surface of the coating layer (see FIG. 2). The inventors have advantageously determined that such depressions, having an average size on the nanoparticle scale of the coating layer, can provide a hydrophobic nano-textured surface (e.g., alone or in combination with the partially exposed nanoparticles).

[0045] Thus, in certain embodiments described elsewhere herein, the outer major surface of the coating layer further comprises a plurality of depressions, in certain such embodiments, the average size of the depressions is within the range of 10 nm to 200 nm, or 25 nm to 200 nm, or 50 nm to 200 nm, or 100 nm to 200 nm, or 10 nm to 150 nm, or 10 nm to 100 nm, or 10 nm to 50 nm, or 25 nm to 150 nm, or 50 nm to 100 nm.

[0046] In certain embodiments described elsewhere herein, the coating layer further comprises a crosslinked silane (e.g., the product of curing a coating composition comprising the crosslinked silane). In certain embodiments described elsewhere herein, the substrate comprises a plurality of hydroxyl groups (e.g., the product of plasma etching the substrate surface). In certain embodiments described elsewhere herein, the substrate surface comprises a fluorinated silane (e.g., the product of depositing a silane onto the substrate surface). In certain embodiments described elsewhere herein, the outer major surface of the article has a water contact angle of at least 130°. For example, in certain such embodiments, the outer major surface has a water contact angle of at least 135°, or at least 140°, or at least 150°, or at least 155°, or at least 160°.

[0047] In certain embodiments, the light transmission through the coating layer of the article is at least 95% for wavelengths in the range of 300 nm to 1500 nm, or for visible wavelengths in the range of 400 nm to 700 nm. In certain embodiments described elsewhere herein, the substrate may also be a light-transmitting material, such as, for example, glass or plastic. In certain embodiments, the substrate is light-transmitting, and the coating layer and substrate allow light (e.g., from a laser or optical sensor) to pass through the substrate and coating layer with relatively little interference (e.g., substantially no interference). EXAMPLES

[0048] Example 1: Formation of a Superhydrophobic Composition An amorphous fluoropolymer binder is dissolved in a fluorinated solvent. Hydrophobic fumed silica nanoparticles are added. Optionally, hydrophobic aerogel nanoparticles are added. The mixture is mixed with a sonic probe to break up agglomerates of the hydrophobic fumed silica particles and hydrophobic aerogel particles, and dried to provide the desired material. Table 1 lists exemplary compositions and the amount of each component as a weight percent of the composition. [Table 1]

[0049] Example 2: Superhydrophobic coating method A hydrophobic silane is added to a mixture of a small amount of water and isopropyl alcohol or acetone to provide a 1% by volume solution of the silane. An optionally plasma etched glass wafer is immersed in the solution, then air dried and heated in an oven at about 100° C. for about 15-20 minutes to provide a silane-functionalized surface.

[0050] A 1-2 wt% coating solution of amorphous fluoropolymer binder is prepared in a fluorinated solvent by stirring the binder powder and solvent at about 50°C for about 10 minutes to provide an optically clear, fully dissolved fluoropolymer solution. This solution is spin coated onto a silane-functionalized wafer to provide a coating of 150-450 nm. The coated wafer is air dried and then heated in an oven at about 200°C for about 60 minutes.

[0051] A nanoparticle coating solution containing 0.1 wt% aerogel nanoparticles and 0.2 wt% silica nanoparticles is prepared in a 1-2 wt% fluoropolymer coating solution by mixing with a sonic probe in 30 minute increments until the nanoparticles are well dispersed. The nanoparticle solution is sprayed onto the coated wafer to provide 50-75 nm nanoparticles partially embedded in the coating layer. The wafer is then air dried and then heated in an oven at about 200 °C for about 60 minutes.

[0052] The refractive index of the resulting coating is about 1.33, and the water contact angle of the coating is about 165°.

[0053] Example 3: Superhydrophobic coating method A coating solution of 2 wt% fluoropolymer binder and crosslinked silane in a fluorinated solvent is spin coated onto a plasma etched glass wafer to provide a coating of 150-450 nm. The coated wafer is air dried and then heated in an oven at about 150° C. for about 60 minutes to provide a crosslinked coating layer.

[0054] A nanoparticle coating solution containing 0.1 wt% aerogel nanoparticles and 0.2 wt% silica nanoparticles is prepared in a 2 wt% fluoropolymer / crosslinked silane coating solution by mixing with a sonic probe for about 3 hours until the nanoparticles are well dispersed. The nanoparticle solution is sprayed onto the coated wafer to provide nanoparticles partially embedded in the coating layer. The wafer is air dried and then heated in an oven at about 150° C. for about 60 minutes.

[0055] The refractive index of the resulting coating is approximately 1.41.

[0056] Example 4: Superhydrophobic coating method A layer of fluoropolymer binder is deposited onto an optionally plasma etched glass wafer using physical vapor deposition (PVD). Following deposition, a nanoparticle coating solution according to Example 2 or 3 is sprayed onto the coated wafer to provide nanoparticles partially embedded in the coating layer. The wafer is air dried and then heated in an oven at 150-200° C. for 60 minutes.

[0057] Example 5: Excessive weathering of the coating The coated wafer of Example 2 was exposed to simulated rain and wind for an extended period of time. A portion of the partially embedded nanoparticles are displaced from the coating, resulting in a surface that contains remaining partially embedded nanoparticles and nanoscale depressions (see FIG. 2). The surface after weathering remains superhydrophobic, with a water contact angle of about 135°.

[0058] It should be understood that the sequences described herein are for illustrative purposes only, and thus, one of skill in the art will recognize that other sequences and other elements can be substituted, and that some elements may be omitted altogether, depending on the desired results.

[0059] While various aspects and implementations are disclosed herein, other aspects and implementations will become apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for illustrative purposes only and are not intended to be limiting, with the true scope and spirit being indicated by the following claims, along with the full scope of equivalents to which such claims are entitled. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

Claims

1. A method for producing a composition, comprising: forming a mixture comprising a hydrophobic fluorinated solvent, a binder comprising a hydrophobic fluorinated polymer, fumed silica nanoparticles, and hydrophobic aerogel nanoparticles; drying the mixture to provide the composition.

2. The method according to claim 1, wherein forming the mixture comprises forming the mixture using a sonication probe.

3. The method according to claim 1, wherein the hydrophobic aerogel nanoparticles are present in the composition in an amount of 0.1 to 0.5% by weight.

4. The method according to claim 1, wherein the hydrophobic aerogel nanoparticles have a surface area of 600 m2 / g to 800 m2 / g.

5. The method according to claim 1, wherein the hydrophobic aerogel nanoparticles have a density of 100 to 200 kg / m3.

6. The method according to claim 1, wherein the hydrophobic aerogel nanoparticles have nano-scale surface irregularities.

7. The method according to claim 1, wherein the average size of the hydrophobic aerogel nanoparticles is in the range of 10 nm to 200 nm.

8. obtaining an aerogel precursor powder comprising aerogel particles having a size greater than 5 microns; mechanically grinding or sonicating the aerogel particles to obtain aerogel particles of a small size. The method according to claim 7, further comprising:

9. The method according to claim 1, wherein the average size of the fumed silica nanoparticles is in the range of 10 nm to 200 nm.

10. The method according to claim 1, wherein the hydrophobic fluorinated solvent comprises a fluorinated alkane, a fluorinated trialkylamine, a fluorinated cycloalkane, a fluorinated heterocycloalkane, or a combination thereof.

11. The method according to claim 1, wherein the hydrophobic fluorinated polymer comprises a fluoroalkyl polymer, a fluoroalkoxy polymer, a perfluoroalkyl polymer, a perfluoroalkoxy polymer, or a combination thereof.

12. The method according to claim 1, wherein the fumed silica nanoparticles comprise silica nanoparticles chemically modified with a hydrophobic silane.

13. The method according to claim 12, wherein the hydrophobic silane is selected from the group consisting of an organosilane, a fluorinated silane, and disilazane.

14. The method according to claim 1, wherein the fumed silica nanoparticles are chemically treated with a fluorinated material.

15. The method according to claim 1, wherein the fumed silica nanoparticles are chemically treated with polydimethylsiloxane (PDMS).

16. The method according to claim 1, wherein the binder is present in the composition in an amount of 0.3 to 1.5% by weight.

17. The method according to claim 1, wherein the binder is present in the composition in an amount of 0.8 to 1.2% by weight.

18. The method according to claim 1, wherein the fumed silica nanoparticles are present in the composition in an amount of 0.01 to 0.5% by weight.

19. The method according to claim 1, wherein the fumed silica nanoparticles are present in the composition in an amount of 0.08 to 0.12% by weight.

20. The method according to claim 1, wherein the binder is amorphous, optically transparent, and soluble in the hydrophobic fluorinated solvent.

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