STABLE AQUEOUS EMULSIONS OF NONPOLAR SILANES HAVING CONSTANT PARTICLE SIZE

Abstract: An aqueous emulsion of a nonpolar silane is disclosed. The emulsion contains an emulsifier system that prevents particle size increase with time. The emulsifier system contains a primary surfactant that prevents coalescence of the particles by ionic repulsion between particles and a cosurfactant. The amounts of each surfactant in the emulsifier system are sufficient to provide an outer mixed monolayer that contacts the water phase and a second inner monolayer of essentially water insoluble cosurfactant. The mixed monolayer is a combination of both surfactants. The surfactant bilayer provides a barrier that prevents diffusion of the silane into the water phase, thereby minimizing diffusion of the silane out of the particle.

Description: STABLE AQUEOUS EMULSIONS OF NONPOLAR SILANES HAVING CONSTANT PARTICLE SIZE FIELD OF THE INVENTION This invention relates to aqueous silane emulsions that can be used in water repellence applications. More particularly, this invention relates to aqueous silane emulsions which do not phase separate with age and that have an average particle size that does not increase significantly with age. BACKGROUND OF THE INVENTION Organosilane and organosilicone compounds dissolved in organic solvents have been used to render masonry and other substrates water repellent in the past. For example, U.S. Patent 3,772,065 to Seiler discloses a method for waterproofing masonry structures. The method comprises impregnating masonry structures with an alcoholic or hydrocarbon solution of hydrolyzed alkyltrialkoxysilanes and their lower oligomers. European Patent 0 075 962 to Pϋhringer discloses an impregnating agent for porous building materials containing tetraalkoxysilanes, alkyltrialkoxysilanes, or aryltrialkoxysilanes, a surfactant, an aliphatic solvent, and an optional condensation reaction catalyst. U.S. Patent 4,937,104 to Pϋhringer discloses a process for imparting hydrophobicity to mineral substrates. The process comprises mixing at least one silane. a hydrolysis product of the silane, a condensation product, or combinations thereof, with a surfactant and a water/ organic alcohol mixture. The resulting emulsion is applied to a mineral substrate. However, organic solvents such as alcohols and hydrocarbons are flammable, expensive, and have detrimental environmental and physiological effects. U.S. Patent No. RE 33,759 to DePasquale et al. discloses an aqueous emulsion containing silanes for rendering masonry surfaces water repellent. The system consists essentially of a hydrolyzable silane, and oligomers thereof; a surfactant having HLB of 4 to 15; and water. The hydrolyzable silane has the formula where n is 1 or 2, R is selected from hydrocarbon and halogenated hydrocarbon groups of 1 to 20 carbon atoms, and R' is selected from alkoxy groups of 1 to 3 carbon atoms, halide groups, amino groups, and carboxyl groups. The surfactant can be nonionic, amphoteric, ionic, or combinations thereof. The preferred surfactants are SPAN® surfactants, which have HLB values in the range of 4.3 to 8.6. and TWEEN® 61 and TWEEN® 81. which have HLB values of 9.6 and 10.0. respectively. However. pH and particle size of the emulsion are not disclosed. Particle size change with time is not disclosed. U.S. Patent No ' s. 4,877,654, and 4.990,377. both to Wilson et al.. disclose aqueous emulsions for rendering porous substrates water repellent. The emulsion comprises a hydrolyzable silane, an emulsifier with HLB of 1.5 to 20, a buffer, and water. The silane has formula R n SiR " 4_ n . where R is selected from hydrocarbon- and halogenated hydrocarbon groups of 1 to 30 carbon atoms; n is 1 or 2, and R " is an alkoxy group of 1 to 6 carbon atoms, a halide group, an amino group, or a carboxyl group. Nonionic. cationic, anionic. and amphoteric emulsifiers are suitable. The emulsion has a pH of 6-8. However, stability and particle size of the emulsion are not disclosed. Particle size change with time of the emulsion is not disclosed. U.S. Patent No. 5,226,954 to Suzuki, discloses an organosilicon composition comprising a monoalkyltrialkoxysilane and/or a condensate thereof, an emulsifier mixture of an anionic emulsifier and a nonionic emulsifier, and water. The composition undergoes emulsification to form an emulsion. 'Emulsification' as defined therein is achieved when the alkylalkoxysilane and the emulsifier are mixed and the resulting upper layer is opaque and further where a small amount of water separates to form a lower layer that is more transparent than the upper layer. Suzuki '954 does not disclose particle size of the emulsion. Suzuki '954 does not disclose particle size increase over time. U.S. Patent No. 5,746,810 to Suzuki discloses an aqueous emulsion of an alkylalkoxysilane, a surfactant, and water. Suzuki '810 discloses that the emulsion is stable and has particle diameter in the range of 2 to 10 micrometers. Suzuki '810 defines 'stable' to mean that after storage, some separation into an opaque layer of silane concentrated emulsion and a colorless transparent layer of water is acceptable when the material can easily be reemulsified. The emulsion has a pH of 7.5-9. United Kingdom Publication GB 2 301 102 A to Toagosei Co., Ltd., discloses an aqueous emulsion prepared by hydrolyzing a silane selected from the group consisting of alkoxysilanes and alkylhalogensilanes by heating in the presence of an acid catalyst and a small amount of water to form a mixture of the silane and its oligomer, and subsequently emulsifying the mixture with water and an emulsifier. The alkoxysilane has the formula R n SiR " 4_ n . where R is selected from alkyl groups, substituted alkyl groups, and aryl groups; n is 1 or 2, and R " is an alkoxy group of 1 to 6 carbon atoms. The emulsifier can be nonionic. anionic, or cationic. The particle size of the emulsion is 1 micrometer or smaller. Emulsions with particle size larger than 1 micrometer tend to be unstable and liable to phase separation. U.S. Patent No. 5,458,923 and U.S. Patent No. 5,314.533, both to Goebel et al., disclose aqueous emulsions of organosilicon compounds. The emulsion comprise an alkoxysilane, an ionic surfactant, an organosilicon surfactant, and water. The emulsion is stable for weeks at pH 6 to 9. 'Stable " is defined as 1. an emulsion having no phase separation and no formation of a layer of cream, or 2. an emulsion that can be reobtained by simple stirring with no loss of effects if a layer of cream does occur. However, none of these patents address the problem of particle size increase with time. This is generally due to a process known as Ostwald Ripening in which the low molecular weight emulsified silane compound has a sufficient solubility in water such that it diffuses from smaller particles through the aqueous phase into larger particles. This results in a net increase in average particle size of the emulsion with time. This can lead to inconsistent behavior or performance of the emulsion in commercial use due to changing properties of the emulsion with age. Additionally, when an alkoxysilane is used as the silane compound in the emulsion, over time the alkoxysilane can react when it contacts the water phase. The alkoxysilane can undergo hydrolysis and condensation, thereby forming a siloxane and liberating alcohol, which can break the emulsion. Therefore, an object of this invention is to provide a means to prevent, or minimize, increasing emulsion particle size with age; producing stable emulsions of low molecular weight silanes. "Low molecular weight" means a molecular weight (MW) less than 1000. Another object of this invention is to provide a means to prevent, or minimize, increasing particle size with age of emulsions of water soluble silanes. Particles of increasing size will cream up more rapidly, in accordance with Stokes Law for the rate of creaming of particles in an emulsion. Conversely, if the particles are sufficiently small, the velocity of random particle movement due to Brownian Motion will be sufficient to prevent creaming. The use of additives in the silane compound phase or water phase to decrease the density difference between the silane compound and water to near zero is one technique to minimize creaming. However, this is often undesirable, as it adds to the manufacturing cost of an emulsion and may have detrimental effects on the use of the emulsion in some applications. To reduce creaming, one may also increase the viscosity of the aqueous phase with thickeners such as alginates. as disclosed in U.S. Patent No. 5,746.810. or with the use of large amounts of emulsifiers relative to the amount of interfacial surface area between the oil particles and the water phase. The use of such large amounts of emulsifier results in the formation of emulsifier structures such as liquid crystals on the particle surface and in the water phase which produces a viscous aqueous phase. Use of excessive amounts of emulsifiers is generally detrimental to the water repellency properties provided by silane emulsions. Therefore, it is a further object of this invention to produce emulsions of silanes having sufficiently small particle size such that they do not exhibit significant creaming and remain essentially stable in uniformity of silane concentration with age. To this end it is an object of this invention to provide emulsions having average particle size less than 10 microns. An emulsion will not change in uniformity due to creaming if the emulsion is so concentrated in dispersed oil particles that it is already a cream from top to bottom of the container. The maximum packing of rigid spheres of the same diameter is 74% by volume. Accordingly, as the concentration of silane phase in a polydisperse particle size emulsion approaches or exceeds this concentration, the emulsion becomes quite viscous and unlikely to exhibit non-uniformity due to creaming, as it is already essentially in a creamed state. Due to the viscous, paste-like nature of such emulsions, they are difficult to pump or handle in commercial use. Therefore, it is a further object of this invention to provide stable and uniform silane emulsions that have low viscosity for ease of handling. The emulsions of this invention have silane concentrations of approximately 65% or less by weight and are easily handled such as by pouring or pumping due to their low viscosity. SUMMARY OF THE INVENTION This invention relates to an aqueous silane emulsion and a method for its preparation. The emulsion comprises an alkoxysilane, an emulsifier system of at least two emulsifiers. and water. One emulsifier is the primary emulsifier. and it is selected from the group consisting of anionic. cationic. and amphoteric emulsifiers. The second emulsifier is a nonionic cosurfactant. and it has an HLB value of less than 1 1. The emulsion has improved stability in that the emulsion of alkoxysilanes exhibits no phase separation with age. The emulsion has uniformity in that the discontinuous phase exhibits no. or minimal, increase in particle size with age. DETAILED DESCRIPTION OF THE INVENTION The aqueous silane emulsions of the present invention are stable and have constant particle size. "Stable" means that the emulsion does not phase separate into a water layer and a silane (oil) layer with age. "Constant" means that the particle size of the emulsion does not increase significantly with age. Preferably, particle size does not increase by more than 10% after the emulsion is stored at about 25°C for at least 14 days. These emulsions are easily handled such as by pouring or pumping due to their low viscosity. Typically, viscosity of the emulsion is not greater than about 5 sq mm/s. Typically, viscosity of the emulsion is not greater than about 5 sq mm/s. However, at silane concentrations greter than 50%, emulsion viscosity will be greater than 5, and may be as high as 1,000 sq mm/s. Emulsions with viscosity in the range of 5 to 1 ,000 sq mm/s are easily poured and pumped. The aqueous silane emulsion comprises: A) a continuous phase comprising water; B) a discontinuous phase comprising at least 1 nonpolar silane, wherein the discontinuous phase forms particles dispersed in the continuous phase; and C) an emulsifier system consisting essentially of (i) a primary surfactant, and (ii) a cosurfactant. This emulsion has the advantage that even a low molecular weight silane can be emulsified to form a stable emulsion with constant particle size. However, it is not meant that this invention is limited to low molecular weight nonpolar silanes. This emulsion can contain nonpolar silanes having molecular weights greater than 1,000. 'Nonpolar silane " means that at least one nonpolar organofunctional group is bonded to the silicon atom. The nonpolar silane is preferably a nonpolar alkoxysilane. Typically, the amount of nonpolar alkoxysilane is 1 to 65 wt% of the emulsion. Preferably, the amount of nonpolar alkoxysilane is from 10 to 60 wt%. however, concentrations as low as 5 to 10 wt% are suitable for some applications. Suitable nonpolar alkoxysilanes have the general formula R n SiR " 4_ n . where each R is independently a monovalent hydrocarbon group. R " is an alkoxy group of 1 to 10 carbon atoms, and n is 1 or 2. R is preferably independently selected from the group consisting of alkyl. halogenated alkyl. aryl and substituted aryl groups. When the emulsion will be used in water repellence applications, preferably R is independently an alkyl group of 8 to 20 carbon atoms and R" has 1 to 6 carbon atoms. However, alkyl groups R having 1 to 7 carbon atoms are also suitable for use in this emulsion. Suitable alkylalkoxysilanes and halogenated alkylalkoxysilanes for component (B) are exemplified by those disclosed by U.S. Patent RE 33,759 to DePasquale et al., which is hereby incorporated by reference for the purpose of disclosing suitable alkoxysilanes. Preferably, the alkylalkoxysilane is selected from the group consisting of isobutyltriethoxysilane, isobutyltrimethoxysilane, n-octyltriethoxysilane, and n- octyltrimethoxysilane. Suitable halogenated alkylalkoxysilanes include 3,3,3-trifluropropyl trimethoxysilane and 6,6,6-trifluorohexyl trimethoxysilane. However, this emulsion is advantageous over the emulsion disclosed by DePasquale et al. because high purity silanes can be emulsified to form stable emulsions having constant particle size. The high purity silanes typically contain about 5 wt% or less of impurities. "Impurity" means any dimer, trimer, or oligomer of the silane; and includes any other siloxane polymer or high molecular weight oil present in the silane. The emulsion of this invention can be produced with a particle size less than 10 micrometers. Preferably, particle size is less than 1 micrometer, and more preferably, particle size is less than 0.5 micrometers. The emulsifier system inhibits particle size increase with age. The emulsifier system comprises a primary surfactant and a cosurfactant. The primary surfactant prevents coalescence of the particles by ionic repulsion between particles. The cosurfactant prevents diffusion of the silane out of the particle, which could result in Ostwald Ripening. The amounts of each surfactant in the emulsifier system are sufficient to provide an outer mixed monolayer that contacts the water phase and a second inner monolayer of essentially water insoluble cosurfactant. The mixed monolayer is a combination of both surfactants. This provides a barrier that prevents diffusion of the silane into the water phase. The surfactant bilayer provides a significant barrier to retard or prevent diffusion of the silane out of the particle. The primary surfactant is selected from the group consisting of anionic, cationic. and amphoteric type emulsifiers. The primary surfactant must be present in the emulsion at a concentration of 0.5 to 3 molecules per 100 square Angstroms of surface area of the silane particles. However, the exact amount of primary surfactant depends on the type of surfactant chosen and. for very dilute emulsions having relatively large particle size where the concentration of primary surfactant becomes low by these constraints, it may be necessary to increase this amount by the critical micelle concentration (CMC) of the emulsifier to adjust for the amount that would be dissolved in the water phase. Anionic surfactants suitable for use as the primary surfactant include sulfonic acid salt derivatives. Suitable anionic surfactants are exemplified by alkali metal sulfosuccinates; sulfonated glyceryl esters of fatty acids such as sulfonated monoglycerides of coconut oil acids; salts of sulfonated monovalent alcohol esters such as sodium oleyl isothionate; amides of amino sulfonic acids such as the sodium salt of oleyl isothionate; amides of amino sulfonic acids such as the sodium salt of oleyl methyl tauride; sulfonated products of fatty acid nitriles such as palmitonitrile sulfonate; sulfonated aromatic hydrocarbons such as sodium alpha- naphthalene monosulfonate; condensation products of naphthalene sulfonic acids with formaldehyde, sodium octahydro anthracene sulfonate; alkali metal alkyl sulfates; ether sulfates having alkyl groups of 8 or more carbon atoms; and alkylaryl sulfonates having one or more alkyl groups of 8 or more carbon atoms. Anionic surfactants are known in the art and are commercially available. For example, suitable anionic surfactants include BIO-SOFT® N-300, a triethanolamine linear alkyl sulfonate available from Stepan Company, Northfield, Illinois; SIPONATE® DS-10, a sodium salt of dodecylbenzene sulfonic acid available from Alcolac Inc., Baltimore, Maryland; and DOWFAX® 8390, a sodium n-hexadecyl diphenyloxide disulfonate, available from the Dow Chemical Company, Midland, Michigan. Cationic surfactants suitable for use as the primary surfactant are typically fatty acid amines, amides, and derivatives and salts of fatty acid amines and amides. Suitable cationic surfactants include aliphatic fatty amines and derivatives such as dodecyl amine acetate, octadecyl amine acetate, and acetates of amines of tallow fatty acids; homologues of aromatic amines having fatty chains such as dodecyl aniline; fatty amides derived from aliphatic diamines such as undecyl imidazoline; fatty amides derived from di-substituted such as oleylamino diethylamine; derivatives of ethylene diamine: quaternary ammonium compounds such as tallow trimethyl ammonium chloride, dioctadecyldimethyl ammonium chloride, didodecyldimethyl ammonium chloride, and dihexadecyldimethyl ammonium chloride; amide derivatives of amino alcohols such as beta-hydroxyethyl stearyl amide; amine salts of long chain fatty acids; quaternary ammonium bases derived from fatty amides of di- substituted diamines such as oleylbenzylamino ethylene diethylamine hydrochloride; quaternary ammonium bases of benzimidazolines such as methyl heptadecyl benzimidazole hydrobromide; basic compounds of pyridinium and derivatives such as cetylpyridinium chloride; sulfonium compounds such as octadecyl chloromethyl ether; urethanes of ethylene diamine such as condensation products of stearic acid and diethylene triamine; polyethylene diamines; and polypropanol polyethanol amines. Suitable cationic surfactants are commercially available. Suitable cationic surfactants include ARQUAD® T-27W, 16-29, C-33, T-50 AND ETHOQUAD® T/13 and T/13 ACETATE, available from Akzo Chemicals Inc.. Chicago, Illinois. Amphoteric surfactants suitable for use as the primary surfactant include cocoamphocarboxyglycinate, cocoamphocarboxypropionate, cocobetaine, N- cocamidopropyldimethylglycine, and N-lauryl-N-carboxymethyl-N-(2- hydroxyethyl)ethylenediamine, quaternary cycloimidates, betaines, and sultaines. Amphoteric surfactants that are commercially available include MIRATAINE® and MIRANOL® available from Rhone-Poulenc Incorporated, Cranberry, New Jersey; and TEGO® BETAINE available from Goldschmidt Chemical Corporation. Hopewell, Virginia. The cosurfactant must have an HLB less than 1 1. Examples of some suitable cosurfactants and their HLB values include: ALDO® MS (3.8-3.9), which is glycerol monostearate, and LONZEST® GMO (3.0), which is an ethoxylated fatty ester, both of which are produced by Lonza Inc.. Fairlawn, New Jersey; S-MAZ® 60K (4.7), which is a sorbitan monostearate available from PPG Industries, Gurnee, Illinois; ARLACEL® 60 (4.7), which is a sorbitan stearate available from ICI Americas Inc., Wilmington, Delaware: oleates such as sorbitan monooleate (4.3). sorbitan trioleate (1.8), polyoxyethylene sorbitan monooleate (10.0); ALDO PGHMS® (3.0), which is propylene glycol monostearate available from Lonza Inc., Fairlawn, New Jersey; MAPEG® EGMS (2.9), which is ethylene glycol monostearate available from PPG/ Mazer Gurnee, Illinois; HODAG® DGS (4.7), which is diethylene glycol monostearate; ETHOX® SAM-2 (4.9). which is a polyoxyethylene stearyl amine available from Ethox Chemicals Inc., Greenville, South Carolina; MACOL® SA-2 (4.9), which is a polyoxyethylene stearyl ester available from PPG/ MAZER. Gurnee, Illinois; and polyoxyethylene ethers such as BRIJ® 72 (4.9). which is a polyoxyethylene lauryl ether and BRIJ® 52 (4.9), which is a polyoxyethylene cetyl ether, both of which are available from ICI Americas Inc.; SPAN® 20 (8.6). which is a sorbitan monolaurate available from ICI Surfactants; and CALGENE® GML (3.0), which is glycerol monolaurate available from Calgene Chemical, Inc. Sorbitan fatty acid esters having HLB values in the range of 4.3 to 8.6 and polyoxyethylene sorbitan fatty acid esters having HLB values in the range of 9.6 to 10 are preferred nonionic cosurfactants. The preferred sorbitan fatty acid esters having HLB values in the range of 4.3 to 8.6 are available commercially under the tradename SPAN®, produced by ICI Americas. SPAN® 20, a sorbitan monolaurate, has HLB of 8.6, SPAN® 40 has HLB of 6.7, SPAN® 60, a sorbitan monostearate, has HLB 4.7, and SPAN® 80 has HLB of 4.3. SPAN® 20 is particularly preferred. Polyoxyethylene sorbitan fatty acid esters having HLB values in the range of 9.6 to 10.0 are commercially available under the tradename TWEEN®, produced by ICI Americas. Particularly preferred are TWEEN® 61, which has HLB of 9.6; and TWEEN® 81 which has HLB of 10.0. The concentration of cosurfactant in the emulsion is 1.5 to 15, preferably 4 to 15, molecules per 100 square Angstroms of surface area of the silane particles. Higher amounts of cosurfactant are unnecessary and may lead to emulsion instability. Emulsion particle sizes cited are "intensity" weighted diameters as measured by dynamic light scattering (photon correlation spectroscopy). A NICOMP® Particle Sizer instrument was used. The balance, up to 100%, of the aqueous silane emulsion comprises water and any optional components. Typically, the amount of water in the emulsion is 30 to 99 weight percent. The aqueous silane emulsion may further comprise one or more of the following optional components: (D) a buffer, (E) a biocide, (F) a thickener, (G) a fragrance, (H) a colorant, (I) a foaming agent, (J) an anti-foaming agent, and (K) a rust inhibitor. Component (D) is an optional buffer used to maintain the pH of the aqueous silane emulsion in a desired range. Buffers are typically organic and inorganic acids and bases, including salts thereof. The amount of buffer added to the emulsion is typically 0.01 to 5 wt%. Suitable buffers are disclosed in U.S. Patent No. 4,877,654, which is hereby incorporated by reference for the purpose of describing suitable buffers. When the emulsion will be used in water repellence applications, the buffer is preferably selected from the group consisting of sodium bicarbonate, sodium benzoate, disodium hydrogen phosphate, and a mixture of ammonium hydroxide and acetic acid. A buffer is preferably added to the emulsion when a biocide is present, or when pH of the emulsion is outside the range of 6 to 9. Component (E) is an optional biocide typically added in an amount of 0.1 to 5 wt% of the emulsion. Biocides are known in the art and are commercially available. For example, 6- acetoxy-2.4-dimethyl-m-dioxane (GIV-GARD DXN®) sold by Guvaudan Corp. is suitable for this invention. Suitable biocides are disclosed in U.S. Patent No.4,877.654. which is hereby incorporated by reference for the purpose of describing suitable biocides. Component (F) is an optional thickener that moderately increases the viscosity of the aqueous phase. Component (F) may be used to prevent creaming of the larger particle size emulsions in this range. The thickener must not affect the stability and particle size of the emulsion. Suitable thickeners are exemplified by water soluble polymers such as polyacrylic acid and polyacrylic acid salts, alginic acid salt, alginic acid ester, polyvinyl alcohol, polyether, casein, mannan, starch, chitosan, carboxymethylcellulose, and methoxymethyl cellulose. U.S. Patent 5,746,810 is hereby incorporated by reference for the purpose of describing suitable thickeners. Thickeners are typically added in an amount of 0.1 to 1 wt% of the emulsion. Component (G) is an optional fragrance. Component (H) is an optional colorant. The colorant can be water based, or it can be an oil-soluble dye. Component (I) is an optional foaming agent. Component (J) is an optional anti-foaming agent. Component (K) is an optional rust inhibitor. Component (K) is, for example, sodium benzoate. The emulsion of this invention can be used in a wide variety of applications, including water repellence applications. This invention further relates to a method for rendering substrates water repellent. The method comprises impregnating the substrate with the aqueous alkoxysilane emulsion, and hydrolyzing and condensing the alkoxysilane. The substrate can be wood, but is preferably masonry. 'Masonry * means any porous inorganic substrate, such as building materials. Masonry includes structural ceramics, cements, insulation products, stone, sheet rock, and concrete. Suitable substrates are disclosed in U.S. Patent 4,877,654, hereby incorporated by reference for the purpose of describing suitable substrates. The method for impregnating the substrate with the aqueous alkoxysilane emulsion is not critical. For example, the emulsion can be applied to a surface of the substrate by brush coating, roller coating, or spraying. Alternatively, the aqueous alkoxysilane emulsion can be mixed with a composition, such as uncured concrete, and thereafter the composition can be cured to form a substrate having water repellency. The amount of emulsion impregnated in the substrate depends on the porosity and surface conditions of the substrate but is typically in the range of 0.05 to 2.0 Kg/sq m. This invention further relates to a method for preparing the emulsion of the present invention. The method comprises: emulsifying a composition comprising A) water; B) at least 1 alkoxysilane, wherein the alkoxysilane forms a discontinuous phase of particles dispersed in the water; and C) an emulsifier system consisting essentially of (i) a primary surfactant, wherein the primary surfactant is a nonionic emulsifier having an HLB greater than 13, and wherein the primary surfactant is present in the emulsion at a concentration of 0.5 to 3 molecules per 100 square Angstrom of surface area of the particles and (ii) a cosurfactant, wherein the cosurfactant is a nonionic emulsifier having an HLB less than 1 1 , and wherein the cosurfactant is present in the emulsion at a concentration sufficient to provide 1.5 to 15 molecules per 100 square Angstroms of surface area of the particles. The emulsion can be made with a desired particle size of the discontinuous phase (i.e., less than 0.5 micrometers) to get the correct range of surfactant coverage on the particles. Particle size can be varied by changing shearing conditions such as sonolation pressure during emulsification. For example, if the particle size and surface coverage is too large, increasing shear or increasing sonolation pressure can be performed to decrease particle size. If particle surface coverage is too low, i.e., because particle size is too small, the shearing intensity can be decreased, additional cosurfactant can be added, or both, as needed. One skilled in the art would know how to adjust particle size by changing shearing conditions. EXAMPLES These examples are intended to illustrate the invention to those skilled in the art and should not be interpreted as limiting the scope of the invention set forth in the claims. All percentages in these examples are weight percentages, unless otherwise indicated. For purposes of these examples. 'n-Otes" means n-octyltriethoxysilane. The surfactants used are shown by tradename in this example. BIOSOFT® N-300 is a triethanolamine linear alkyl sulfonate, an anionic surfactant. SPAN® 20 is sorbitan monolaurate with HLB of 8.6. The equation used to calculate gamma (T), which is number of surfactant molecules per 100 square Angstroms of particle surface area, is shown below: -3 r = % S x D ÷ (9.96 x 10 x M x % silane), where S is the weight percent of the emulsifier in the emulsion, D is the initial particle size (diameter) of the silane particles in nanometers, and M is the molecular weight of the emulsifier. Reference Example 1 An emulsion of a silane was prepared by mixing 12 parts water with the primary surfactant until the primary surfactant was completely mixed with the water. Then 40 parts of the silane were mixed with the cosurfactant and added to the above water mixture. The resulting mixture was stirred at 2000 RPM with a 1.5 inch diameter Cowls blade for 30 minutes. After 30 minutes an additional 58.3 parts water was added and the resulting mixture was processed through a 2 stage homogenizer at 7500/1500 psi. After homogenizing the mixture, 0.001 parts of sodium bicarbonate was added to the mixture to maintain a pH of approximately 7.0. The initial particle size of the resulting emulsion was measured by a NICOMP® particle size analyzer. Particle size is reported in nanometers, unless otherwise indicated below. Based on the amount of primary surfactant added and the initial particle size, a coverage of primary surfactant per 100 square Angstroms of particle size was generated according to the formula above. Similarly, based on the amount of cosurfactant and the initial particle size, a coverage of cosurfactant per 100 square Angstroms of particle size was generated according to the forumula above. The particle size of the emulsion was measured after storage at room temperature. When a clear water layer was visually observed on the bottom of the emulsion, the emulsion was deemed to have failed stability. Table 1 shows the primary surfactant and the amount used, the cosurfactant and the amount used, the silane used, and the amount of water used. Table 2 shows the coverage of primary surfactant and cosurfactant and the particle size measured over time for each sample, until the sample failed stability. Example 1 Sample 1 was an emulsion of N-octyltriethoxysilane was prepared by the method of Reference Example 1. The primary surfactant, sodium laural sulfate, is an anionic surfactant present at 2.8 molecules per 100 square Angstroms of particle surface area. The cosurfactant, SPAN® 20 is a nonionic surfactant, which is a sorbitan monolaureate, having an HLB value of 8.6. Sample 1 was tested for particle size by the method in Reference Example 1. Example 1 shows that stable emulsions of constant particle size can be produced using an ionic primary surfactant with a nonionic cosurfactant having HLB less than 11. Example 2 Sample 2 was an emulsion of N-octyltriethoxysilane was prepared by the method of Reference Example 1. The primary surfactant is BIOSOFT® N-300, a triethanolamine linear alkyl sulfonate, which is an anionic surfactant. The cosurfactant, SPAN® 20 is a nonionic surfactant, which is a sorbitan monolaureate, having an HLB value of 8.6. Sample 2 was tested for particle size by the method in Reference Example 1. Example 2 shows that stable emulsions of constant particle size can be produced using an different ionic primary surfactants with a nonionic cosurfactant having HLB less than 11. Table 1 Examples: Sample Formulations Sample 1 Sample 2 Silane n-Otes 40.00% n-Otes 40.00% Primary Sodium Laural 1.00% BIOSOFT® 1.00% Surfactant Sulfate N-300 o- Surfactant SPAN® 20 2.00% SPAN® 20 2.00% Water 57.00% 57.00%

Claims: We claim: 1. An aqueous emulsion comprising: A) a continuous phase comprising water; B) a discontinuous phase comprising at least 1 nonpolar alkoxysilane, wherein the discontinuous phase forms particles in the continuous phase; and C) an emulsifier system consisting essentially of (i) a primary surfactant selected from the group consisting of anionic emulsifiers. cationic emulsifiers. and amphoteric emulsifiers. wherein the primary surfactant is present in the emulsion at a concentration sufficient to provide 0.5 to 3 molecules of primary surfactant per 100 square Angstroms of surface area of the particles; and (ii) a cosurfactant, wherein the cosurfactant is a nonionic emulsifier having an HLB less than 1 1, and wherein the cosurfactant is present in the emulsion at a concentration sufficient to provide 1.5 to 15 molecules per 100 square Angstroms of surface area of the particles. 2. The emulsion of claim 1, wherein the nonpolar alkoxysilane is present from 1 to 65 wt% of the emulsion. 3. The emulsion of claim 1, wherein the nonpolar alkoxysilane has a molecular weight of less than 1,000. 4. The emulsion of claim 1 , wherein the nonpolar alkoxysilane has general formula R n SiR' _ n , wherein each R is independently selected from the group consisting of alkyl, halogenated alkyl, aryl, and substituted aryl groups, R' is an alkoxy group of 1 to 6 carbon atoms, and n is 1 or 2. 5. The emulsion of claim 4, wherein R is independently an alkyl group of 1 to 20 carbon atoms. 6. The emulsion of claim 5, wherein R is independently an alkyl group of 1 to 7 carbon atoms. 7. The emulsion of claim 1. wherein the primary surfactant is an anionic triethanolamine linear alkyl sulfonate. 8. The emulsion of claim 1 , wherein the cosurfactant has an HLB value less than 9. 9. The emulsion of claim 1 , wherein the concentration of the cosurfactant is sufficient to provide 4 to 15 molecules of cosurfactant per 100 square Angstroms of surface area of the particles. 10. The emulsion of claim 1 , wherein the particles have an average diameter of less than 10 micrometers. 1 1. The emulsion of claim 10, wherein the average diameter is less than 1 micrometer. 12. The emulsion of claim 1, further comprising one or more optional components selected from the group consisting of (D) a buffer, (E) a biocide, (F) a thickener. (G) a fragrance, (H) a colorant, (I) a foaming agent, (J) an anti-foaming agent, and (K) a rust inhibitor. 13. The emulsion of claim 12, wherein the buffer is selected from the group consisting of organic and inorganic acids and bases, and salts of organic and inorganic bases. 14. The emulsion of claim 12, wherein the biocide is present from 0.1 to 5 wt% of the emulsion. 15. The emulsion of claim 12, wherein the thickener is selected from the group consisting of polyacrylic acid and polyacrylic acid salts, alginic acid salt, alginic acid ester, polyvinyl alcohol, polyether, casein, mannan, starch, chitosan, carboxymethylcellulose. and methoxymethyl cellulose. 16. The emulsion of claim 12. wherein the colorant is selected from the group consisting of water based colorants and oil-soluble dyes. 17. The emulsion of claim 12, wherein the rust inhibitor is sodium benzoate. 18. A method comprising: I) emulsifying a composition comprising A) a continuous phase comprising water; B) a discontinuous phase comprising at least 1 alkoxysilane. wherein the discontinuous phase forms particles dispersed in the continuous phase; and C) an emulsifier system consisting essentially of (i) a primary surfactant, wherein the primary surfactant is selected from the group consisting of anionic surfactants, cationic surfactants, amphoteric surfactants, and combinations thereof, and wherein the primary surfactant is present in the emulsion at a concentration of 0.5 to 3 molecules per 100 square Angstrom of surface area of the particles, and (ii) a cosurfactant, wherein the cosurfactant is a nonionic emulsifier having an HLB less than 1 1, and wherein the cosurfactant is present in the emulsion at a concentration sufficient to provide 1.5 to 15 molecules per 100 square Angstroms of surface area of the particles; and II) forming an adsorbed inner layer consisting essentially of the cosurfactant between the discontinuous phase and an outer layer of consisting essentially of a combination of the primary surfactant and the cosurfactant, wherein the combination contacts the aqueous phase. 19. The method of claim 18, wherein the concentration of cosurfactant is 4 to 15 molecules per 100 sq Angstroms of particle size, thereby minimizing size increase of the particles such that the particles do not increase in size by more than 10% after the emulsion is stored at about 25°C for at least 14 days.

Inventors: FISHER PAUL D, GEE RONALD P, FISHER, PAUL, D., GEE, RONALD, P.
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1999
Main classification: C04B41
IPC codes: B01F17, C04B41, C08G77, C08J3, C09D183, C09K3