WO2008045022A2

WO2008045022A2 - Additive particles having superhydrophobic characteristics and coatings and methods of making and using the same

Info

Publication number: WO2008045022A2
Application number: PCT/US2006/031035
Authority: WO
Inventors: Bryan E. Koene; Martin E. Rogers; Jonas C. Gunter
Original assignee: Luna Innovations Incorporated
Priority date: 2006-08-09
Filing date: 2006-08-09
Publication date: 2008-04-17
Also published as: WO2008045022A3

Abstract

Additive particles may be employed in sufficient amounts to impart superhydrophobicity to a coating system in which the additive particles are incorporated. The additive particles include carrier microparticles and a dense plurality of nanoparticles adhered to the surfaces of the carrier microparticles (e.g., preferably by electrostatic deposition or covalent bonding). The additive particles are advantageously incorporated into a coating material (e.g., a polymeric material) in amounts sufficient to render a substrate surface superhydrophobic when coated with the coating material. The substrate may be rigid (e.g., glass, ceramic or metal) or flexible (e.g., a polymeric film or sheet or a fabric).

Description

ADDITIVE PARTICLES HAVING SUPERHYDROPHOBIC

CHARACTERISTICS AND COATINGS AND METHODS OF

MAKING AND USING THE SAME

GOVERNMENT RIGHTS STATEMENT This invention was made with Government support under Grant

No. W91 1 NF-04-C-084 awarded by the Defense Advanced Research Projects Agency (DARPA) and Grant No. FA9550-05-C-0061 issued by the Air Force Office of Scientific Research. The Government has certain rights to the invention.

FIELD OF THE INVENTION

The present invention relates generally to additive particles that may be incorporated into matrices. In preferred forms, the present invention relates to additive particles that may be incorporated into polymeric matrices to form a coating that will impart superhydrophobic characteristics to substrates coated with the same.

BACKGROUND AND OF THE INVENTION

Various proposals exist in the art for the production of superhydrophobic coatings. See in this regard, Shang et al, "Nanostructured superhydrophobic Surfaces", J. Mater. ScL 40 (2005) 3587; Lau et al, "Superhydrophobic Carbon Nanotube Forests", Nano

Letters, 3 (2003) 1701 ; Ren et al, "Preparation and Characterization of an Ultrahydrophobic Surface Based on a Stearic Acid Self-Assembled Monolayer over Polyethyleneimine thin Films", Surface Science, 546 (2003) 64; Mock et al, 'Towards Ultrahydrophobic Surfaces: A Biomimetic Approach", J. Phys.: Condens. Matter 17 (2005) S639; and Fresnais et al, "Polyethylene Ultrahydrophobic Surface: Synthesis and Original Properties" Eur. Phys. J. Appl. Phys. 26 (2004) 209, the entire content of each such prior publication being expressly incorporated hereinto by reference.

While superhydrophobic properties may in fact be achieved by the techniques disclosed in the prior publications identified above, they are typically limited by substrate size (i.e., are not suitable for coating onto a large substrate area), are time consuming and/or are not sufficiently robust for surface finishes. For example, the production of nanofibers by electrospinning cannot be used in a paint or coating application and is limited to relatively small substrates. Nanotubes produced on a surface by vapor deposition (or other methods) are limited to small substrates; require high temperature substrates and cannot be used in a coating. Self-assembled multilayers are likewise limited in substrate size and are impractical commercially due to their time consuming (e.g., several days) to produce a suitable structure. Photolithographic processes are not applicable as coating as they are limited in substrate size and require high temperature substrate. Plasma treatment process are not applicable as a coating; are limited in substrate size and are cost-prohibitive to use on a meaningful commercial scale.

Recently, the superhydrophobic behavior of the lotus leaf structure has been mimicked by providing a honeycomb-like polyelectrolyte multilayer surface with silica nanoparticles and then coating such highly textured surface with a semifluorinated silane. See, Zhai et al, "Stable

Superhydrophobic Coatings from Polyelectrolyte Multilayers", Nano Letters 4 (2004) 1349-1353, the entire content of which is expressly incorporated hereinto by reference. SUMMARY OF THE INVENTION

Broadly, the present invention is embodied in additive particles which may be employed in sufficient amounts to impart superhydrophobicity to a coating system in which the additive particles are incorporated. In especially preferred embodiments, the additive particles of the present invention comprise carrier microparticles and a dense plurality of nanoparticles adhered to the surfaces of the carrier microparticles (e.g., preferably by electrostatic deposition or covalent bonding). In some preferred embodiments of the present invention, the additive particles are incorporated into a coating material (e.g., a polymeric material) in amounts sufficient to render a substrate surface superhydrophobic when coated with the coating material. The substrate may be rigid (e.g., glass, ceramic or metal) or flexible (e.g., a polymeric film or sheet or a fabric).

These and other aspects and advantages will become more apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Reference will hereinafter be made to the accompanying drawings, wherein like reference numerals throughout the various FIGURES denote like structural elements, and wherein;

FIGURE 1 A is an enlarged schematic cross-sectional view of an exemplary additive particle in accordance with the present invention;

FIGURE 1 B is an enlarged schematic cross-sectional view of another exemplary additive particle in accordance with the present invention; FIGURE 2 is an enlarged schematic cross-sectional view of a coated substrate in accordance with the present invention which exhibits superhydrophobic properties;

FIGURES 3A and 3B are scanning electron microscope (SEM) images at 500X and 200,00OX magnification, respectively, of polymer carrier microspheres of approximately 50 μm effective diameter with SiO₂ nanoparticles of approximately 20 nm adhered to the surface;

FIGURE 4 is an SEM image at 290,54OX showing the additive particles made in accordance with Example 2 below;

FIGURE 5A is an SEM images at 177,00OX magnification of SiO₂ carrier microparticles of approximately 0.4 μm effective diameter with SiO₂ nanoparticles of approximately 20 nm adhered to the surface which were made in accordance with Example 5, invention sample number 9 below;

FIGURE 5B is an SEM images at 177,00OX magnification of SiO₂ carrier microparticles of approximately 0.4 μm effective diameter with SiO₂ nanoparticles of approximately 70 nm adhered to the surface which were made in accordance with Example 5, invention sample number 18 below;

FIGURE 6 is a photograph showing the superhydrophobic properties of a coated microscope slide made in accordance with Example 5, invention sample number 1 below: and

FIGURES 7A and 7B are photographs at 2OX and 3OX magnification, respectively, showing the superhydrophobic properties of a coated textile substrate made in accordance with Example 8 below. DETAILED DESCRIPTION OF THE INVENTION A. Definitions

The terms below as used herein and in the accompanying claims are intended to have the following definitions.

"Filament" means a fibrous strand of extreme or indefinite length.

"Fiber" means a fibrous strand of definite length, such as a staple fiber.

"Yarn" means a collection of numerous filaments or fibers which may or may not be textured, spun, twisted or laid together.

"Fabric" means a collection of filaments, fibers and/or yarns which form an article having structural integrity. A fabric may thus be formed by means of conventional weaving, braiding, knitting, warp-knit weft insertion, spinbonding, melt blowing techniques to form structurally integrated masses of filaments, fibers and/or yarns.

'Textile article" is used generically to refer to filaments, fibers, yarns and fabrics. For convenience, the discussion below will reference textile articles, it being understood that such reference embraces filaments, fibers, yarns and fabrics.

"Functionalized" means that a material has been imbued with an ability to form a covalent bond with another functionalized material. For example, the materials employed according to the present invention may be imbued with amino, epoxy and/or halo functionality.

"Pigment" is meant to refer to a solid particulate material that may be incorporated or dispersed in a sea of matrix material. Additive particles may thus have generally circular or noncircular cross-sectional configurations.

"Nano" is meant to refer to a structure having an effective diameter of nanometer (nm) dimensions. The term nanoparticles is therefore intended to refer to three dimensional particulate structures having an average diameter of nano dimensions.

"Micro" is meant to refer to a structure having an effective diameter of micrometer (μm) dimensions. A microparticle is therefore intended to refer to three dimensional particulate structures having an average diameter of micro dimensions.

"Effective diameter" is meant to refer to the diameter of the smallest sphere which entirely encompasses a three dimensional particulate structure.

"Synthetic" means that the material is man-made from a substance and includes polymers synthesized from chemical compounds, modified or transformed natural polymers, and minerals. Synthetic fibers are thus fibers which are made from a man-made substance and are distinguishable from natural fibers such as cotton, wool, silk and flax.

"Superhydrophobic" means that a 1 μ\ sessile droplet of water on a surface forms a contact angle (θ) of greater than 150° using the drop shape method of contact angle measurement. The contact angle (θ) is the slope of the tangent to a sessile droplet on a film surface at the liquid- solid-vapor (LSV) interface line as calculated from the mathematical expression θ = 2 tan^'1 2h/d, where h and d represent the height and diameter, respectively, in millimeters of the sessile droplet . It will also be understood that when an element is referred to as being "on", "attached" to, "connected" to, "coupled" with, "contacting", etc., another element, it can be directly on, attached to, connected to, coupled with or contacting the other element or intervening elements may also be present. In contrast, when an element is referred to as being, for example, "directly on", "directly attached" to, "directly connected" to, "directly coupled" with or "directly contacting" another element, there are no intervening elements present. It will also be appreciated by those of skill in the art that references to a structure or feature that is disposed "adjacent" another feature may have portions that overlap or underlie the adjacent feature.

Spatially relative terms, such as "under", "below", "lower", "over", "upper" and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the structure in the figures is inverted, elements described as "under" or "beneath" other elements or features would then be oriented "over" the other elements or features. Thus, the exemplary term "under" can encompass both an orientation of "over" and "under". The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. Similarly, the terms "upwardly", "downwardly", "vertical", "horizontal" and the like are used herein for the purpose of explanation only unless specifically indicated otherwise. B. Description of the Preferred Embodiments

Accompanying FIGURE 1A depicts in very schematic fashion a cross-section of an exemplary additive particle 10 in accordance with the present invention. As shown, the additive particle 10 is essentially comprised of a carrier microparticle 12 and a dense plurality of nanoparticles 14 adhered on an exterior surface thereof. The dense plurality of nanoparticles 14 will impart superhydrophobic character to a coating material.

FIGURE 1 B depicts another possible embodiment of an additive particle 10' in accordance with the present invention which is substantially the same as the additive particle 10 depicted in FIGURE 1A, but includes a carrier microparticle 12' which is hollow having an interior space 12a defined by the particle wall 12b. The additive particle 1,0 may thus be advantageous in coating systems employing the same as its lesser density will allow it to migrate to an exposed surface of the coating system when coated onto a substrate. Although not shown, the nanoparticles 14 adhered to the surface of the carrier microparticles 12 or 12' may likewise be hollow. For ease of discussion, reference will be made below only to the additive particle 10 depicted in FIGURE 1A, but it should be understood that such a reference applies equally to additive particle 10' discussed above.

The exemplary coated substrate 15 in accordance with the present invention shown in accompanying FIGURE 2 generally comprises a coating system 16 coated upon a substrate 18. As shown schematically therein the coating system 16 is comprised of the additive particles 10 incorporated into a polymeric coating material 20. The coating system 16 may thus be applied as a coating layer onto the underlying substrate 18. In this regard, the coating material 20 serves as a matrix to bind the particles 10 to an underlying substrate 18 and thereby form the coated substrate 15.

As shown, the substrate 18 is depicted as being a synthetic or natural textile material (e.g., cotton, polyester, nylon or the like). Using a textile material as the substrate 18 is however merely a presently preferred embodiment of the invention, as the substrate 18 could be any form of material to which the coating system 16 may be applied so as to impart superhydrophobicity. Thus, the substrate 18 may be formed of a rigid material (e.g., glass, ceramic, metal or the like), or may be in the form of a flexible film or sheet (e.g., a polymeric film, paper sheet or the like).

Also as shown, the additive particles 10 are depicted as being concentrated near the exposed surface of the coating material 20. As will be described in greater detail below, it is the exposure of the additive particles 10 at the surface of the coating material 20 which is believed to contribute substantially to the superhydrophobic properties that are achieved. Alternatively, the additive particles may be dispersed substantially homogenously throughout the thickness of the coating material 20 in which case a greater amount of the additive particles 10 may be needed in order to achieve comparable superhydrophobic properties.

The carrier microparticles 12 most preferably have an effective diameter of less than about 200 μm, more preferably between about 0.015 to about 150 μm, and most preferably between about 0.10 to about 100.

In certain embodiments, the carrier microparticlesj 2 will have an effective diameter of between about 0.50 to about 60 μm. The nanoparticles 14 most preferably have an effective diameter of less than 200 nm, preferably between about 1 nm to less than 200 nm, more preferably between about 1 to about 100 nm, and most preferably between about 5 to about 70 nm.

The carrier microparticle 12 and nanoparticles 14 adhered on its surface may be formed of the same or different material. Exemplary materials from which the microparticle 12 and nanoparticle 14 may be formed include natural and synthetic inorganic and/or organic materials. In preferred embodiments, the carrier microparticles 12 and nanoparticies 14 may be formed of the same or different inorganic metal oxide.

Preferred inorganic metal oxides include, for example, silica, alumina and titania. Silica is especially preferred. Other inorganic materials that may be employed in the practice of the present invention include metals and metal alloys, non-metal oxides, phosphates, phosphonates, nitrides, sulfides, sulfates, halides or other materials commonly employed in the art in the form of particulates. While not wishing to be bound to any particular theory, it is not presently believed that the composition of the microparticle 12 and/or nanoparticles 14 contributes significantly to the ultimate superhydrophobicity that is achieved in accordance with the present invention. Instead, it is presently surmised that it is the morphology that is achieved by means of the nanoparticles 14 being adhered onto the surface of the carrier microparticles that achieves the superhydrophobicity properties of the resultant coatings.

The additive particles 10 in accordance with the present invention may be made by binding the nanoparticles 14 to the exterior surface of the carrier microparticle 12, most preferably by means of electrostatic deposition or covalent bonding. With electrostatic deposition, electrically charged nanoparticles 14 (i.e., either cationically or anionically charged nanoparticle may be deposited on the surface of a microparticle 12 of opposite electrical charge (i.e., anionically or cationically charged, respectively). The charging of the microparticles 12 and nanoparticles 14 may be accomplished using techniques well known to those in the art. For example, charged microparticles 12 may be introduced into an electrostatic spray of oppositely charged nanoparticles 14 so as to cause the latter to be electrostatically bound to the surface of the former.

Covalent bonding of the microparticles 12 and nanoparticles14 may also be accomplished using known covalent bonding techniques. Thus, for example, one of the microparticles 12 and nanoparticles 14 may be functionalized with surface epoxide groups while the other of the microparticles 12 and nanoparticles 14 may be functionalized with surface an amine groups. The functionalized microparticles 12 and nanoparticles 14 may then be brought into contact with one another under conditions which cause the epoxy groups to react with the amine groups thereby causing the nanoparticles 14 to be covalently bonded to the microparticles. Surface functionality may be achieved using other reactive moieties and reaction techniques well known to those in the art, including for example, halogen groups, hydroxy! groups, cyano groups and the like.

The coating material 20 may be any material which is compatible with the additive particles 10. Most preferably, the coating material 20 is a polymeric material selected from thermoplastic polymers (e.g., polyolefins, polyamides, polycarbonates, polyesters, and polystyrene), curable polymers (e.g., polyacrylics, polyepoxides, polyureas, and poiysilicones) and the like. The additive particles 10 may be dispersed into the coating material 20 while the latter is in a liquid form (e.g., in a melt phase, solvent phase or the like) by mixing the additive particles using known techniques. The liquid coating material 20 with the additive particles 10 dispersed therein may then be applied to the substrate 18 in a conventional manner, for example, by spraying, roll coating, dipping, pouring, padding or the like. The liquid coating material 20 with the additive particles 10 dispersed therein may then be allowed to solidify (e.g., by cooling, solvent removal, radiation curing, heat curing or the like) on the substrate 18 to thereby form a coating layer of the coating system 16 thereon.

Alternatively, the liquid coating material 20 may first be applied onto the surface of the substrate 18 and, while still liquefied, the additive particles 10 may be brought into contact with the coating material 20 (e.g., by spraying the additive particles onto the liquid coating material 20).

Thereafter, the coating material 20 may be allowed to solidify on the surface of the substrate 18 to thereby form a coating layer of the coating system 16 thereon.

The amount of the additive particles 10 employed in the coating material 20 is sufficient to impart superhydrophobic properties to the coated substrate 15. Thus, the amount of the additive particles 10 is such that the additive particles 10 are exposed sufficiently to cause the coated substrate 15 to exhibit a contact angle of greater than about 150° for a 1μl water droplet. Most preferably, the additive particles 10 are present in an amount so as to achieve an exposure of at least about 10 %, preferably at least about 90% per unit area of the coating material 16. Thus, the percentage of the additive particles that will preferably be exposed range between about 10% up to 100%.

^■ The amount of surface exposure of the additive particles 10 may be enhanced by incorporating the additive particles 10 in a coating material

20 which has a greater apparent density. That is, the superhydrophobic nature of a coating or surface treatment is dependant upon the surface characteristics of the coating system 16. Thus, only the first several nanometers of the coating thickness of the coating system 16 is directly responsible for the ultimate wettability of the coating. Therefore, it is desirable for the additive particles 10 o be concentrated at the surface of the coating system 16.

One way to achieve such apparent density difference between the additive particles and the coating material 20 is to employ hollow carrier microparticles 12a (e.g., as shown in FIGURE 1B). Additive particles 10' prepared from hollow carrier microparticles 12a as described herein will therefore allow the additive particles 10' to rise to the surface of the coating system 16 layer due to their lower apparent density. As such, the use of hollow carrier microparticles 12a will be advantageous since a lesser quantity of the additive particles 10' may be employed to achieve superhydrophobic properties as compared to the case in which the additive particles are more uniformly distributed through the thickness of the coating. In some embodiments therefore the apparent density of the additive particles 10 or 10' will be at least about 5%, and preferably at least about 20% less than the apparent density of the coating material 20.

In general, the additive particles 10 or 10' will typically be incorporated into the coating material 20 in an amount between about 5 to about 50 wt.%, and preferably between about 5 to about 20 wt.%, based on the total weight of the coating system 16 (i.e., the weight of both the additive particles 10 and the coating material 20). As described above, a lesser amount of some additive particles (e.g., those based on hollow carrier microparticles and/or hollow nanoparticles) may be employed to ^• achieve comparable superhydrophobicity since the additive particles present will be concentrated near the layer surface of the coating system 16 on the substrate 18. However, a greater amount of additive particles may be needed if the particles are to be distributed more homogenously throughout the coating thickness.

The actual coating layer thickness of the coating system 16 is not critical. Thus, coating thicknesses of about 0.5 mil or greater may be applied onto the underlying substrate. Preferably, however, coating layer thicknesses of between about 1 mil to about 10 mil may be employed, with coating thicknesses between about 2 to about 6 mil being especially preferred.

The present invention will be further understood from the following non-limiting Examples.

EXAMPLES

Example 1 - Particle Surface Treatment

A. Amino functionalized silica (SiO₂: NH₂)

3-aminopropyl triethoxysilane, NH₂(CH₂)₃Si(OC₂H₅)₃, (0.2 g, 0.90 mmol) was added to 95% ethanol (50 ml). The pH of the solution was lowered to about 5 with the addition of acetic acid, and was allowed to stand for 5 minutes. SiO₂ particles with an average diameter of about 60 μm (1 g) was added, and the suspension was treated in an ultrasound bath for 20 minutes. The ethanolic suspension was heated to dryness on a hot plate, and the resulting powder was then heated in an oven at 110⁰C overnight to remove excess silane and obtain amino functionalized silica particles. This technique was repeated using silica particles of the following average diameters: 60μm, 40μm, 14μm, 12μm, 0.5μm, and 0.25μm. B. Epoxide functionalized silica (SiO₂: Epoxy)

The technique described above in Example 1 A with reference to the amino functionalized silica was repeated except that 3- glycidyloxypropyl (trimethoxy)silane (0.2g, 0.85 mmol) was reacted with the silica particles to obtain epoxide functionalized silica particles.

C. Fluorine functionalized silica (SiO₂:F)

The technique described in Example 1 A above with reference to the amino functionalized silica was repeated except heptadecafluoro(1 ,1 ,2,2-tetrahydrodecyl)trimethoxy silane (CF₃(CF2)7(CH2)2Si(OCH₃)3) (0.2g, 0.33 mmol) was reacted with the silica particles to obtain fluorine functionalized silica particles.

Example 2 - Co va lent bonding of nanoparticles onto carrier microparticles

Amino functionalized silica nanoparticles of selected sizes 15 - 500 nm) prepared according to Example 1A above were reacted with epoxy functionalized silica carrier microparticles of selected sizes (12 - 60 μm). the amino functionalized silica nanoparticles (0.1 g) were suspended in ethanol (50 ml), following which the epoxy functionalized silica carrier microparticles (1 g) were added). The solution was stirred for 1 hour under sonication, followed by stirring overnight. The solid was filtered out and dried at 100⁰C in air. Scanning electron microscopy (FIGURE 4) confirmed that the surface of the carrier microparticles were covered by nanoparticles. Example 3 - Electrostatic deposition of nanoparticles onto carrier microparticles

Anionic silica nanoparticles (Snowtex 40, 20-40 nm average particle diameter, Snowtex 2OL, 40-50 nm average particle diameter and Snowtex Zl 70-100 nm average particle diameter - Nissan Industries) were deposited electrostatically onto cationic micron sized silica carrier particles. The electrostatic deposition process was performed by stirring the ammonium functionalized silica obtained in Example 1 D above. The ammonium functionalized silica (1g) was suspended in 80 ml H₂O, followed by the addition of 2 ml of the anionic silica nanoparticles. Upon stirring for 2 hours, the material was filtered, washed with water and dried at 100⁰C overnight. Scanning electron microscopy showed that the surface of the microparticles is covered by nanoparticles. The surface of the microparticles was then treated with fluoro functionality using the method described previously in Example 1C.

Example 4

Titania particles can be used as either the carrier particle or the nanoparticle in a similar fashion.

A. Titania carrier with silica surface particle - Titania particles with a diameter of 15 nm (Nanostructured and Amorphous

Materials Inc) were used in place of silica as in Example 1 A. The same ratios of ingredients were used to functionalize them with amino groups. To these were attached 10-20 nm anionic silica nanoparticles (Snowtex 40) by the same method as in Example 3. B. Silica carrier particle with titania surface particle -

Conversely, anionic colloidal titania (NanoTek titania (5 nm), NanoPhase -*— Technologies) can be used in place of the anionic silica to place titania on the surface of silica by the same method as Example 3. Example 5 - Superhvdrophobic coating material prepared bv surface application of additive particles

A two-component curable polyurethane coating material (Desothane^® HS polyurethane commercially available from PRC-Desoto International) was mixed in the manufacturer required ratios (3:1 (v/v) Part A and Part B). The polyurethane coating material was cast onto glass microscope slides to a dry thickness of 2 to 6 mils. Before complete curing could occur (i.e., within about 2 minutes of casting), additive particles made in accordance with Example 3 above were applied onto the top surface of the coating so as to give a substantially uniform coverage. The coating material was then allowed to cure at room temperature. Static contact angle measurements were obtained using 1 μ\ droplets of water and a commercially available contact angle instrument (Model 125 from First Ten Angstroms of Portsmouth, VA). The results appear in Table 1 below.

Table 1 - Droplet Contact Angles for Coatings

It will be observed that use of only the carrier microparticle in the coating material did not impart superhydrophobicity (i.e., Comparative Samples 2-5 all had contact angles of less than 150°). In contrast, the additive particles in accordance with the present invention (i.e., Invention

Samples 1-19) imparted superhydrophobicity to the coating material since contact angles of 150° and greater were obtained.

Example 6 - Superhydrophobic coating material prepared by direct blending of additive particles with coating material Example 1 was repeated except that the additive particles having

20 nm nanoparticles electrostatically adhered to the surface of 60 μm carrier particles made in accordance with Example 3 were directly blended with the polyurethane coating material in the amounts specified in Table 2 below. Specifically, 100, 200 and 300 milligrams (mg)of the additive particles were added per gram of the polyurethane coating material along with 1 ml of butyl acetate. The coating solution was blended and cast at a dry thickness of between 2-6 mil onto glass microscope slides and allowed to cure at room temperature following which contact angles were determined. The results appear in Table 2 below.

Table 2

Example 7 - Additional coating materials containing the superhydrophoblc additive particles

Example 1 was repeated except that the additive particles of Invention Sample 6 were incorporated into other commercially available coating materials as identified in Table 3 below. Contact angles were determined for the "neat" coating material (i.e., having no additive particles) and for the modified coating material (i.e., having additive particles incorporated therein). The results are shown in Table 3 and demonstrate that the additive particles of the present invention may be employed across a variety of coating material platforms so as to impart superhydrophobicity to coated substrates.

Table 3

Example 8 - Preparation of superhvdrophobic fabrics

100 mg of hydrophobic particles (40 nm SiO₂ / 15 nm TiO₂) were add to 2g of a commercially available textile finishing solution (2U41-347 available from Shawmut Inc.). After mixing for 6 minutes, a swatch of fabric (50:50 cotton:polyester) was wetted with the solution in a Petri dish.

The excess solution was removed by pressing with a roller over the fabric. The swatch was then heated at 120⁰C for 2 hours. The swatch was then treated with heptadecafluoro-1 ,1 ,2,2-tetrahydrodecyl)trimethoxy silane (CF₃(CF2)7(CH₂)₂Si(OCH₃)3) (0.2 g, 0.33 mmol) in ethanol (10 g). After heating at 11O⁰C for 1 hour, the hydrophobicity of the fabric was determined by measuring the contact angle of a sessile droplet on the modified fabric surface. The fabric exhibited a contact angle of 155°. Accompanying Figures 7A and 7B show the superhydrophobicity of the modified fabric surface at a magnification of 2OX and 3OX, respectively.

Example 9 - Polymeric microsphere synthesis

Polyacrylic acid microspheres were prepared by the reverse emulsion polymerization of acrylic acid. A solution of sodium hydroxide (90 g) dissolved in water (360 ml) was added dropwise to acrylic acid (216 g) at 5°C. Methylenebisacrylamide (15 g) was added to the monomer solution in small increments with stirring. Meanwhile, SPAN 80 (35 g) was dissolved in toluene (1750 g) in a stirred reactor purged with nitrogen. Potassium peroxydisulfate (12.6 g) was added prior to addition of the monomer solution. The monomer solution was added to the toluene solution in 10 ml aliquots with vigorous stirring using an overhead stirrer while the temperature was maintained below 5O⁰C. The resultant solid particles were filtered, washed with acetone and dried under vacuum. These particles had a diameter of about 50 μm, and were anionically charged.

_{***********************************}

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. An additive particle comprising a carrier microparticle, and a dense plurality of nanoparticles adhered to a surface of the microparticle.

2. The additive particle of claim 1 , wherein the carrier microparticle has an effective diameter of less than about 200 μm.

3. The additive particle of claim 1 , wherein the nanoparticles have effective diameters of less than about 200 nm.

4. The additive particle of claim 1 , wherein the carrier microparticle has an effective diameter of between about 0.10 to about 100 μm, and wherein the nanoparticles have effective diameters of between about 1 to 100 nm.

5. The additive particle of claim 1 , wherein the carrier microparticle has an effective diameter of between about 0.50 to about 60 μm, and wherein the nanoparticles have effective diameters of between about 5 to 70 nm.

6. The additive particle of claim 1 wherein the carrier microparticle and nanoparticles are formed of the same or different material selected from metal' oxides, non-metal oxides, metals, metal alloys, phosphates, phosponates, nitrides, sulfides, sulfates, and halides.

7. The additive particle of claim 1 , wherein the carrier microparticle and nanoparticles are formed of the same or different metal oxide.

8. The additive particle of claim 1 , wherein at least one of the microparticle and nanoparticles is formed of a metal oxide.

9. The additive particle of claim 8, wherein the metal oxide is silica oxide or titanium dioxide.

10. The additive particle of claim 9, wherein both the microparticle and nanoparticles are formed of silica oxide.

11. The additive particle of claim 9, wherein one of the microparticle and nanoparticle is formed of silica oxide, and the other of the microparticle and nanoparticle is formed of titanium dioxide.

12. The additive particle of claim 1 , wherein at least one of the carrier microparticie and nanoparticles is hollow.

13. A coating system which comprises a coating material, and additive particles of claim 1 incorporated with the coating material in an amount sufficient to impart superhydrophobic properties to a substrate surface coated with the coating system.

14. The coating system of claim 13, wherein the coating material is a polymeric material.

15. The coating system of claim 13, wherein the additive particles have an apparent density which is sufficiently less than the coating material to allow the additive particles to migrate to a surface of the coating material.

16. A substrate having a surface coated with the coating system of claim 13 so as to establish superhydrophobic properties.

17. The substrate of claim 16, wherein the coating material is a polymeric material.

18. The substrate of claim 17, wherein the polymeric material is selected from thermoplastic polymers, thermoset polymers and curable polymers.

19. The method of claim 16, wherein the substrate is a rigid material selected from glass, ceramic, or metal.

20. The method of claim 16, wherein the substrate is a flexible material or may be in the form of a flexible material selected from films or sheets.

21. The method of claim 20, wherein the substrate is a fabric.

22. A method of making an additive particle comprising adhering a plurality of nanoparticles to a surface of a carrier microparticle.

23. The method of claim 22, wherein the nanoparticles are adhered electrostatically or covalently.

24. The method of claim 22, wherein the nanoparticles and carrier microparticles are each functional ized so as to be covalently bound one to another.

25. The method of claim 24, wherein the nanoparticles and carrier microparticles are each functionalized with a functional group selected from amino, epoxy and halo groups.

26. The method of claim 22, wherein the nanoparticles and carrier microparticle exhibit opposite electrical charges so that the nanoparticles may be electrostatically deposited onto a surface of the microparticle.

27. A method of making a coated substrate having superhydrophobic properties comprising coating a substrate surface with a coating system as in claim 13.

28. The method of claim 27, wherein the additive particles are concentrated at an exposed surface region of the coating system.

29. The method of claim 27, wherein the additive particles are substantially homogenously dispersed throughout the coating system.

30. The method of claim 27, wherein the substrate is a rigid material selected from glass, ceramic, or metal.

31. The method of claim 27, wherein the substrate is a flexible material or may be in the form of a flexible material selected from films or sheets.

32. The method of claim 31 , wherein the substrate is a fabric.