WO2008098069A1

WO2008098069A1 - Directed migration of hydrophobic nanomaterials at surfaces

Info

Publication number: WO2008098069A1
Application number: PCT/US2008/053206
Authority: WO
Inventors: Sang Beom Lee; Lacramioara Schulte Auf'm Erley; Gregory M. Berube
Original assignee: Nanodynamics, Inc.
Priority date: 2007-02-06
Filing date: 2008-02-06
Publication date: 2008-08-14

Abstract

The present application relates to a composition having a layer of hydrophobic nanoparticles at the surface thereof, and a water-based or hydrophilic-based composition. The application further relates to methods of obtaining a desirable surface property of a composition, including mixing hydrophobic nanoparticles in the composition and allowing at least some of the nanoparticles to migrate to a surface of the composition, so that there is a concentration of hydrophobic nanoparticales at the interface.

Description

DIRECTED MIGRATION OF HYDROPHOBIC NANOMATERIALS AT SURFACES

BACKGROUND

[0001] A coating is the application of a thin functional film to surfaces, such as, paper, textiles, metals, wood and polymeric-based materials. Coating processes include immersion, spraying, and powder coating methods, depending on substrate types and properties. Functional films are defined as coatings that have a specific function(s), or property. By coating surfaces with functional films, specific mechanical, electronic, optical, scratch resistant and biological properties can be obtained.

[0002] Other coating methods have also been used. For example, one such coating methods is described in LeIe et al., ("Enhancing Bioplastic - Substrate Interaction via pore induction and directed migration," 2004, Biotech, and Bioeng., 88; 6; 628-636). [0003] Gregory et al., ("Fat, moisture, and ethanol migration through chocolates and confectionary coatings," 2002, Crit Rev Food Sci Nutr., 42(6):583-626) described the migration of fat, moisture, and ethanol in chocolate-coated confectionery products. Migration of one of these components into the coating leads to visual and sensory defects such as sugar or fat bloom, making the product unacceptable to the consumer. U.S. Patent No. 6,797,052 describes methods for using activated carbon for producing moisture-blocking durable cement. Activated carbon powder was used in a cement formulation having vinyl polymers that results in eliminating the problem of moisture retention due to void formation during mixing and atmospheric moisture uptake. In the compositions and methods described, it has been determined that an adduct formed from the interaction of the activated carbon and vinyl polymers fills voids typically present in finished concrete products. The adduct within the voids results in a hydrophobic cement composition.

[0004] U.S. Patent 7,153,357, Baumgart et al., "Coating material, related production method and use" describes a coating material comprising at least one kind of hydrophobic nanoparticles based on silica and at least one kind of hydrophilic nanoparticles based on silica. When the hydrophobic nanoparticles are used in the clearcoat materials in amounts which produce good scratch resistance, the clearcoats in question are scratch-resistant but have a matte finish, while the use of hydrophilic nanoparticles in contrast improves the clarity, transparency, and evenness of the clearcoats. [0005] U.S. Patent 6,495,624, James F. Brown, "Hydrophobic coating compositions, articles coated with said compositions, and processes for manufacturing same" describes compositions of hydrophobic coatings and processes to coat articles with the compositions. The composition consists of a hardenable resin, hydrophobic microparticles having an average particle size diameter of about 100 microns or less and a substantially nonvolatile mobile fluorinated compound.

[0006] U.S. Patent No. 7,081,234, Yu Qi et al, "Process of making hydrophobic metal oxide nanoparticles" describes a process of treating metal oxide nanoparticles that includes mixing metal oxide nanoparticles, a solvent, and a surface treatment agent that is preferably a silane or siloxane. The treated metal oxide nanoparticles are rendered hydrophobic by the surface treatment agent being surface attached thereto, and are preferably dispersed in a hydrophobic aromatic polymer binder.

[0007] U.S. Patent No. 6,033,781, Brotzman, Jr. et al., "Ceramic Powders coated with siloxane star-graft polymers" describes a coated ceramic powder comprising a plurality of ceramic particles and a siloxane star-graft coating polymer encapsulating at least a portion of the particles.

[0008] As is generally known, a myriad of harmful bacteria inhabit peripheral equipment commonly used in daily life. In particular, various bacteria live wherever moisture and oxygen are available and can cause a variety of diseases and disorders. Generally, silver (Ag), copper (Cu), zinc (Zn) and the like are metals that have been shown to exhibit antibacterial activity. Silver cations (Ag+) directly and strongly bind to -SH, -COOH and -OH groups, which are present in bacteria, thereby destroying cell membranes or disturbing cellular functions. Furthermore, silver can catalyze the conversion of oxygen into active oxygen species having sterilizing action, thereby exerting antibacterial functions via sterilizing mechanisms of active oxygen species.

BRIEF DESCRIPTION OF INVENTION

[0009] The present application relates to a composition comprising a layer of hydrophobic nanoparticles at the surface thereof, and a water-based or hydrophilic-based composition. The application further relates to methods of obtaining a desirable surface property of a composition, including mixing hydrophobic nanoparticles in the composition and allowing at least some of the nanoparticles to migrate to a surface of the composition, so that there is a concentration of hydrophobic nanoparticles at the interface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The following description of embodiments can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:

[0011] Figure 1 illustrates a schematic representation of the technology;

[0012] Figure 2 shows a SEM image of hydrophobic nanosilver-aqueous polyurethane thin film; the image shows that the hydrophobic nanosilver migrated at the surface, forming a monolayer;

[0013] Figure 3 shows SEM images of paint samples with nanosilver and hydrophobic nanosilver;

[0014] Figure 4 shows the amount of silver ions released from different nanosilver-paint formulations;

[0015] Figure 5 shows a SEM image of paint sample with hydrophobic nanosilver, after washing in water for 3 weeks;

[0016] Figure 6 shows the aqueous ink spot test on cement samples to evaluate hydrophobicity;

[0017] Figure 7 shows the hydrophobicity of cements containing different amount of fluorinated halloysite;

[0018] Figure 8 shows the water penetration test of cement samples after the immersion of cement samples in water for 12 hrs;

[0019] Figure 9 shows antibacterial activity of latex paints treated with 50ppm stearic acid-coated silver nanoparticles, compared with untreated latex paints; and

[0020] Figure 10 shows antibacterial activity of water-based coatings treated with 25ppm and 50ppm stearic acid-coated silver nanoparticles, compared with untreated latex paints.

DETAILED DESCRIPTION OF INVENTION [0021] The present invention will now be described with occasional reference to the specific embodiments of the invention. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete. [0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for describing particular embodiments only and is not intended to be limiting of the invention. As used in the description of the invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety.

[0023] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth as used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless otherwise indicated, the numerical properties set forth in the following specification and claims are approximations that may vary depending on the desired properties sought to be obtained in embodiments of the present invention. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical values, however, inherently contain certain errors necessarily resulting from error found in their respective measurements.

[0024] The present invention relates to methods of modifying nanoparticles to become hydrophobic, surface modification of hydrophobic nanoparticles, and use of hydrophobic nanoparticles or modified hydrophobic nanoparticles in compositions for providing desired surface properties. In some embodiments, compositions with nanoparticles concentrated at the surface have advantages in providing compositions with unique characteristics and in cost savings, as a smaller quantity of rare or expensive materials are required to obtain a desired functionality.

[0025] In some embodiments, the hydrophobic nanoparticles are provided in water-based compositions. During the drying process of the water-based compositions having hydrophobic nanoparticles, the hydrophobic nanoparticles migrate toward the air-water interface and become concentrated at this interface. Due to the higher concentration of the nanoparticles at the air- exposed surface of the coating or other composition formed from the water-based compositions, as compared to the opposite surface, the final surface properties are enhanced, as compared to the properties of the coating or other composition when mixed with non-modified nanoparticles. In other embodiments, the composition is not water-based, but hydrophilic, and the nanoparticles migrate toward an air-liquid interface.

[0026] In some examples, nanoparticles are treated with hydrophobic compounds to render them hydrophobic. These hydrophobic nanoparticles or nanoparticles that are already hydrophobic are then incorporated into any suitable composition or matrix in which they can migrate at or to the air-liquid interface. In some examples, this migration occurs while the nanoparticles are being mixed into a water-based composition. In other examples, this migration occurs while the nanoparticles are being mixed into hydrophilic-based materials or compositions. In other examples, the migration occurs after the mixing step has been completed and the composition is left essentially undisturbed. A schematic illustration of the migration is shown in Figure 1.

[0027] Nanoparticles with unique properties (e.g. antimicrobial, magnetic, detoxification, catalytic, etc.) can be incorporated in different compositions to obtain materials with different properties. By migration of hydrophobic nanoparticles to the air-liquid interface, more nanomaterials are readily available at the surface; in this way less material may be needed to obtain the same properties.

[0028] Any suitable nanomaterial may be used as a component of the hydrophobic nanoparticles of the present invention. Suitable nanomaterials include, but are not limited to, nanoparticles such as metal nanoparticles (Ag, Cu, Au, Pt, Ni, etc), oxide metal nanoparticles (TiO₂, ZrO₂, MgO, SiO₂, ZnO, Al₂O₃, Nb₂O₅, WO₃, Ta₂O₅, HfO₂, SnO₂, SiAlO_{3 5}, SiTiO₄, ZrTiO₄, Al₂TiO₅, ZrW₂O₈, LiClO₄, CaCO₃, MoO₃, Mo, V₂O₅, CdSe, Sb₂O₅, Pd, Fe₃O₄, Kaolin, Sulfur, CdSe, CdS, CoFe₂O₄, etc), carbon black, silica, halloysite, aluminosilicats (natural and synthetic clays), polymer nanoparticles, and carbon nanotubes, semiconducting quantum dots (CdSe, CdSe/ZnS, CdTe/CdS, PbSe, PbS, InGaP/ZnS), inorganic and organic nanomaterials, and naturally occurring nanomaterials, or combinations thereof. In some examples, the nanoparticles can have at least one dimension less than lOOnm, 50nm, or 30nm. [0029] In other examples, the nanoparticles may be naturally occurring or synthetic nanotubes or nanospheres that contain active ingredients intended to be delivered or released, or both. Any suitable active ingredients may be used. It will be understood that active ingredients may be selected to provide a desired property. For example, suitable active ingredients include, but are not limited to, fertilizers, sun blocking agents, pharmaceuticals, antimicrobial agents, anti-fungal agents, sporicidal agents, antiseptics, water treatment agents, fire retardants, fire suppressant chemicals, pigments, dyes, flavorants, odorants, pesticides, sun blocking agents, pharmaceuticals, drugs, insecticides, herbicides, repellants, pheromones, hormones, nutrients, fertilizers, antibiotics, drugs, enzymes, DNA and therapeutic substances, or combinations thereof.

[0030] In yet other examples, the hydrophobic nanoparticles may be unmodified or can be modified with functional groups, including but not limited to, amino-, carboxy-, and alkyl- silanes and amino-, carboxy-, and alkyl-thiols, or biochemicals such as proteins, nucleic acids, carbohydrates. In addition, the functional particles can be modified with molecular receptors to sense outside chemical or biological compounds.

[0031] The nanoparticles may be modified in any suitable manner to render the nanoparticles hydrophobic. For example, the nanoparticles may be modified with a surface treatment to render the nanoparticles hydrophobic. In some examples, the nanoparticles may be modified with hydrophobic coatings by chemical or physical bonding. Any suitable amount of hydrophobic coating or coatings may be used. The chemical or physical bonding may occur in any suitable manner. For example, the hydrophobic coatings can be chemically bound by covalent bonding, electrostatic interaction, hydrogen bonding, Van der Waals forces, ionic interaction, or physically absorbed onto the nanoparticle surfaces.

[0032] Any suitable hydrophobic coatings may be used. For example, suitable hydrophobic coatings include, but are not limited to, alkyl trichlorosilane derivatives, alkyl trialkoxysilane derivatives, fluoro-based silanes, fatty acids (e. g. stearic acid), Aerosol-OT (sodium bis(2-ethylhexyl) sulfosuccinate), natural and synthetic lipids, activated carbon, thiol compounds, silicon polymers, fluoropolymers, vinyl monomers, cationic, anionic and neutral surfactants, and copolymers and combinations thereof.

[0033] In some examples, nanoparticles may be rendered hydrophobic by performing suitable chemical reactions to grow polymer coatings from the surface of nanoparticles. Such chemical reactions include, but are not limited to, polycondensation, free radical polymerization and controlled radical polymerization methods, such as atom transfer radical polymerization (ATRP), nitroxide mediated polymerization (NMP), and reversible addition fragmentation transfer polymerization (RAFT).

[0034] The hydrophobic nanoparticles may have any suitable dimensions. For example, the hydrophobic nanoparticles can have sizes between lnm and 500 μm, for example, 5nm, IOnm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, lOOnm, 150nm, 200nm, 300nm, 400nm, 500nm, 600 nm, 700nm, 800nm, 900nm, 1 μm, 5μm, lOμm, 50μm, lOOμm, 250μm, or 500μm.

[0035] Hydrophobic nanomaterials may be added to any suitable compositions to provide desired surface properties or other properties to the compositions in any suitable manner. In some examples, the hydrophobic nanoparticles are provided in water-based or hydrophilic-based compositions. The hydrophobic materials migrate to the air- liquid interface of the composition, which is at the surface of the composition. In some embodiments, the hydrophobic materials migrate to the surface while the composition is drying. For example, the compositions may include, but are not limited to, latex paints, water-based coatings, such as aqueous polyurethane coatings, pulp and paper materials, wood fiber based materials, foam, cotton fibers, textiles, membranes, porous or textured metal surfaces, porous ceramics, cementuous materials, glass materials, fiberglass, grout, stucco, sealants, caulks, medical/industrial adhesives for wound dressing, or combinations thereof.

[0036] The hydrophobic nanoparticles may be provided in the compositions in any suitable manner and in any suitable amount. For example, one source of the hydrophobic nanoparticles may be mixed in the compositions or applied on or in the compositions in any suitable manner. In some examples, the hydrophobic nanoparticles are provided in a solution with the composition. In some examples, the hydrophobic particles are provided on or in the composition in a solution. As the solution dries, some of the hydrophobic particles migrate to the surface. In other examples, the hydrophobic particles comprise between about 0.001% and about 50% by weight of the compositions, for example less than about 0.005%, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 5%, 10%, and 20%. In other examples, hydrophobic nanoparticles can be provided by mixing, spraying, dipping, vacuum-impregnating and painting the hydrophobic nanoparticles, solutions, or compositions containing these hydrophobic nanoparticles to suitable surfaces or in suitable compositions.

[0037] In some examples, other hydrophobic materials may be added to the compositions to provide additional surface properties such as water repellency, color, and mechanical properties to the surface of the material. Such hydrophobic materials include, but are not limited to, alkyl trichlorosilane derivatives, alkyl trialkoxysilane derivatives, fluoro-based silanes, fatty acids (e. g. stearic acid), aerosol-OT (sodium bis(2-ethylhexyl) sulfosuccinate), natural and synthetic lipids, activated carbon, thiol compounds, silicon polymers, fluoropolymers, vinyl monomers, cationic, anionic and neutral surfactants and copolymers and combinations thereof [0038] Once the hydrophobic nanoparticles have migrated to the surface of the composition, the nanoparticles can be formed into a layer, in some examples. In other examples, the assembled surface layer of hydrophobic nanoparticles can be polymerized or cross-linked by radiation, heat, chemicals or any other method for polymerization initiation. [0039] Surfaces treated using these methods may benefit not only from the hydrophobicity imparted by the hydrophobic nanomaterials that migrated to the surface, but also from the resultant higher concentration of the exposed nanoparticles at the surface. In some examples, the layer of hydrophobic nanoparticles at the surface of the composition is a significant percentage of the total hydrophobic nanoparticles in the composition, for examples, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75, 80%, 85%, 90% or more. In a preferred embodiment, a majority of the hydrophobic particles in the composition migrate to the layer at the surface of the composition. In some embodiments, hydrophobic nanoparticles are considered to be at part of the surface layer if they are within lOOOnm or less of the surface, for example, 800nm, 500nm, 400nm, 350nm, 300nm, 250nm, 200nm, 150nm, or lOOnm. In a preferred embodiment, the hydrophobic nanoparticles form a monolayer on the surface of the composition. In other embodiments, the nanoparticles are considered to be part of the layer at the surface if they are within a depth from the surface equal to less than 50% of the depth of the composition, for example, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, 2%, 1%, 0.5%, or 0.25%.

[0040] In some embodiments, the layer of hydrophobic nanoparticles at a surface of the composition is a detectable localized concentration of the nanoparticles, wherein the concentration of nanoparticles is greater than that of the composition as a whole, and wherein the width and breadth of the concentration along the surface is greater that the depth of the concentration below the surface. In some embodiments, the layer may be a monolayer wherein the depth of the layer is predominantly only one hydrophobic nanoparticle thick. In some embodiments, the layer is continuous over a surface of a composition. In other embodiments, the layer of hydrophobic nanoparticle is discontinuous, for example, when another hydrophobic material fills space at the surface.

[0041] In some embodiments, the water-based or hydrophilic-based compositions suitable to the invention are those which allow the hydrophobic nanoparticles to migrate to form a layer at the surface within a period of time appropriate for the application of the composition. In the case of coating compositions, such as paints, the water-based or hydrophilic-based composition should allow for the formation of a nanoparticle layer before drying is complete following application. In some embodiments, the layer of hydrophobic nanoparticles forms within less than 24 hours, for example in 18 hours, 12 hours, 6 hrs, 2 hours, 1 hour, 30 minutes, 10 minutes or 5 minutes.

[0042] In one example, silver nanoparticles in water are mixed with different concentrations of stearic acid to render them hydrophobic. The interaction between silver particles and stearic acid can be electrostatic or simply physical absorption. The concentration of stearic acid can be between 0.1 and 10%, for example, about 0.2, 0.5, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, or 9%, depending on the desired degree of hydrophobicity.

[0043] In another example, silver nanoparticles in toluene are mixed with different concentrations octadecyltrimethoxysilane (OTMS), triethoxy(octyl)silane (OTES), or lH,lH,2H,2H-perfluorooctyltriethoxysilane (POTS). The concentration of these silane compounds can be between 0.1 and 10%, for example, about 0.2, 0.5, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, or 9%, depending on the desired degree of hydrophobicity. The interaction between nanomaterials and silane compounds are based on covalent bonding. Ηalloysite nanotubes as a natural nanotubular structure can be modified with stearic acid, OTMS, OTES, or POTS in the same manner.

[0044] The present invention will be better understood by reference to the following examples which are offered by way of illustration and not limitation.

EXAMPLES: [0045] Example 1. Stearic acid-coated silver nanoparticles were mixed by vigorously mixing (1300 rpm) into aqueous polyurethane at concentrations varying from 100 ppm to 1000 ppm. After drying of the resultant composition, scanning electron micrograph (SEM) images were taken to evaluate the migration of the stearic acid-coated silver nanoparticles to the polyurethane surface. SEM images show that stearic acid-coated silver nanoparticles accumulated at the air/water interface in the polyurethane composition and thereby formed a layer on the surface of the polyurethane coating as seen in Figure 2.

[0046] Example 2. Stearic acid-coated silver nanoparticles were mixed by vigorously mixing (1300 rpm) into latex paint at concentrations varying from 150 ppm to 1000 ppm. After drying, SEM images where taken of the paint containing stearic acid-coated silver nanoparticles. These images showed that the stearic acid-coated silver nanoparticles had migrated to the latex paint surface, as seen in Figure 3. To see the increased release of silver ions from paint containing hydrophobic silver nanoparticles, paint samples were immersed in water for 3 weeks. At certain times, aliquots were taken and the amount of silver ion release was determined by ICP-AES. Stearic acid-coated silver nanoparticles were mixed in water-based paint. As a control, uncoated silver nanoparticles were also mixed in a water-based paint. The amount of silver ions released was higher in the case of stearic acid-coated silver nanoparticle-paint than in the case of uncoated silver nanoparticles-paint as seen Figure 4. Paint samples where washed in water for 3 weeks and SEM images were taken (see Figure 5). The electron micrograph shows that during washing step, more nanoparticles are becoming available at the paint surface.

[0047] Example 3. POTS-modifϊed halloysite nanotubes were mixed into cement at concentrations varying from 100 ppm to 10,000 ppm. After drying of the cement samples, aqueous blue ink solution was used to evaluate the hydrophobicity of cement samples. Ink spot test shows that at least some hydrophobically coated halloysite nanotubes migrate to the surface and result in a good water proofing property, as seen in Figure 6. Moreover, the water did not penetrate through the cement containing 1% POTS-modified halloysite nanotubes. Figure 7 shows that even adding 1000 ppm POTS to cement can impede water absorption. To evaluate the stability of the hydrophobically modified halloysite in cement, both regular cement and the cement containing POTS-modified halloysite were immersed in 100 ml water for 12 hrs, and after drying, one drop of ink was added on each cement sample. Both of the two immersed cement samples were different; when ink drops were added on the cement samples, a bigger ink spot was observed than that of water-untreated cements. Significantly, the ink spot on hydrophobic cement was bigger than that on regular cement. However, on the back of cement samples, there was a significant difference between regular and hydrophobic cements as seen in Figure 8. Ink penetrated regular cement but did not penetrate hydrophobic cement at all. One possible explanation, while in no way being limiting on the invention, is that aqueous ink tried to move to the edge (outside) instead of the inside of the cement because hydrophobic cement repels ink. On the other hand, a smaller spot was observed on regular cement because the ink lost opportunity to move to the edge as most of the ink was absorbed by cement.

[0048] Example 4. Evaluation of antibacterial activity of the stearic acid-coated silver nanoparticles.

[0049] Stearic acid-coated silver nanoparticles were prepared by adding 1% stearic acid

(by weight, reported to silver) to the 30nm silver particles solution, before drying. After drying, stearic acid-coated silver particles (as powder) were mixed by vigorously mixing (1300 rpm) into both latex paints and water-based coatings. Both latex paint and water-based coatings were applied in thin films on filter paper coupons (3 cm in diameter) and tested for there effect on the growth of bacteria. Tests were performed against both Gram positive (Staphyloccocus aureus) and Gram negative (Escherichia colϊ) bacteria. The results showed that latex paints that contain 50ppm stearic acid-coated 30nm silver nanoparticles killed 100% of both E. coli and Staph after a 3 hour incubation (see Figure 9). Water-based coatings that contain 25 ppm and 50ppm stearic acid-coated 30nm silver nanoparticles, killed 100% of E.coli after 2 hours (see Figure 10). Water-based coatings contain 25ppm stearic acid-coated silver nanoparticles killed 100% of Staph after a 4 hour incubation and those with 50ppm stearic acid-coated silver nanoparticles killed 100% of Staph after a 3 hour incubation (see Figure 10).

[0050] Example 5. . The hydrophobicity of some exemplary hydrophobically modified nanomaterials along with unmodified nanomaterials in the present invention were measured and the results summarized in Table 1. Nanoparticles were fixed to double sided tape and placed on a goniometer. Water droplets were placed on each of the samples and the angle of the liquid- solid interface was measured. The contact angle observed is a measure of hydrophobicity, with a greater contact angle indicating greater hydrophobicity.

Table 1. Contact angles of various nanoparticles on stick tape

Materials Contact Angle (CA)

30 nm silver nanoparticle coated with stearic acid 132

30 nm silver nanoparticle coated with OTMS 127

Halloysite coated with OTMS 149

Halloysite coated with POTS 151

Kaolin coated with OTMS 137

Halloysite 0

30 nm silver nanoparticle 0

Claims

What is Claim is:

1. A composition comprising: a layer of hydrophobic nanoparticles at the surface thereof, and a water-based or hydrophilic-based composition.

2. The composition of Claim 1, wherein the hydrophobic nanoparticles comprise metal nanoparticles, oxide metal nanoparticles, carbon black, silica, halloysite, aluminosilicats, polymer nanoparticles, carbon nanotubes, semiconducting quantum dots, organic nanomaterials, naturally occurring nanomaterials, or nanospheres.

3. The composition of Claim 2, wherein the hydrophobic nanoparticles are hydrophobic silver particles or hydrophobic halloysite nanotubes.

4. The composition of Claim 1, wherein a majority of the hydrophobic nanoparticles in the composition are at a depth at or below the surface which is less than 50% of the depth of the composition.

5. The composition of Claim 1, wherein the hydrophobic nanoparticles comprise a chemically or physically bonded hydrophobic coating.

6. The composition of claims 5, wherein the hydrophobic coating comprises one or more selected from the group consisting of alkyl trichlorosilane derivatives, alkyl trialkoxysilane derivatives, fluoro-based silanes, fatty acids, Aerosol-OT (sodium bis(2-ethylhexyl) sulfosuccinate), natural and synthetic lipids, activated carbon, thiol compounds, silicon polymers, fluoropolymers, vinyl monomers, cationic, anionic and neutral surfactants and copolymers.

7. The composition of Claim 6, wherein the hydrophobic coating comprises stearic acid, octadecyltrimethoxysilane (OTMS), triethoxy(octyl)silane (OTES), or

IH, lH,2H,2H-perfluorooctyltriethoxysilane (POTS).

8. The composition of Claim 1, wherein the hydrophobic nanoparticles are less than about lOOnm when measured in one dimension.

9. The composition of Claim 1, wherein composition comprises one or more of the group consisting of latex paints, water-based coatings, such as aqueous polyurethane coatings, pulp and paper materials, wood fiber based materials, foam, cotton fibers, textiles, membranes, porous or textured metal surfaces, porous ceramics, cementuous materials, glass materials, fiberglass, grout, stucco, sealants, caulks, medical adhesives, industrial adhesives, or combinations thereof.

10. The composition of Claim 1, wherein the composition has antibacterial activity.

11. The composition of Claim 1, wherein the concentration of nanoparticles in the composition is less than about lOOOppm.

12. The composition of Claim 11, wherein the concentration of nanoparticles in the composition is less than about lOOppm.

13. The composition of Claim 12, wherein the concentration of nanoparticles in the composition is less than about 25ppm.

14. A method of obtaining a desirable surface property of a composition, comprising mixing hydrophobic nanoparticles in the composition and allowing at the nanoparticles to migrate to a surface of the composition, so that there is a concentration of hydrophobic nanoparticles at the surface.

15. The method of Claim 14, further comprising a drying step.

16. The method of Claim 14, wherein the desirable surface property is selected from the group consisting of antibacterial activity, hydrophobicity, magnetism, or catalytic activity.

17. The method of Claim 14, wherein the hydrophobic nanoparticle comprises one or more of the group consisting of comprise metal nanoparticles, oxide metal nanoparticles, carbon black, silica, halloysite, aluminosilicats, polymer nanoparticles, carbon nanotubes, semiconducting quantum dots, organic nanomaterials, naturally occurring nanomaterials, or nanospheres.

18. The method of Claim 17, wherein the hydrophobic nanoparticles are hydrophobic silver particles or hydrophobic halloysite nanotubes.

19. The method of Claim 14, wherein the hydrophobic nanoparticle comprises a chemically or physically bonded hydrophobic coating.

20. The method of claims 19, wherein the hydrophobic coating comprises one or more selected from the group consisting of alkyl trichlorosilane derivatives, alkyl trialkoxysilane derivatives, fluoro-based silanes, fatty acids, Aerosol-OT (sodium bis(2-ethylhexyl) sulfosuccinate), natural and synthetic lipids, activated carbon, thiol compounds, silicon polymers, fluoropolymers, vinyl monomers, cationic, anionic and neutral surfactants and copolymers.

21. The method of Claim 20, wherein the hydrophobic coating comprises stearic acid, octadecyltrimethoxysilane (OTMS), Triethoxy(octyl)silane (OTES), or

IH, 1H,2H,2H-Perfluorooctyltriethoxysilane (POTS).

22. The method of Claim 14, wherein the hydrophobic nanoparticles are less than about lOOnm when measured in one dimension.

23. The method of Claim 14, wherein the composition comprises one or more of the group consisting of latex paints, water-based coatings, such as aqueous polyurethane coatings, pulp and paper materials, wood fiber based materials, foam, cotton fibers, textiles, membranes, porous or textured metal surfaces, porous ceramics, cementuous materials, glass materials, fiberglass, grout, stucco, sealants, caulks, medical adhesives, industrial adhesives, or combinations thereof.

24. The method of Claim 14, wherein the concentration of nanoparticles in the composition is less than about lOOOppm.

25. A composition made by the method of Claim 14.