Surfactants are well known compounds that are used in many fields for providing low surface tension resulting in increased wettability, spreadability, emulsifiability, dispersibility, penetrability, and improved adhesion.
All surfactants are comprised of a hydrophobic segment, a hydrophilic segment, and a connecting linkage of intermediate polarity joining the two segments together. Surfactants are classified as cationic, anionic, amphoteric, or nonionic depending on whether the hydrophilic segment contains, respectively, a cationic group, an anionic group, both a cationic and an anionic group, or a nonionic hydrophilic group. The nonionic hydrophilic segment, generally, is a polyoxyalkylene group, such as the product of oligomerization of ethylene oxide, but may also be a polyhydroxylated group such as sorbitol or glycerol, their alkyl ether derivatives, or their polyoxyalkylene derivatives. Amine oxide surfactants are also classified as nonionic, having only formal charges in the N--O hydrophile. The hydrophobic segment has generally been a long chain hydrocarbyl group, a polyfluorinated aliphatic group, or a polysiloxane group.
Examples of nonionic surfactants having, for instance, a linear or branched, alkyl or alkylaryl, hydrocarbyl hydrophobic segment and a polyethylene oxide hydrophilic segment where the two segments are joined by an ether connecting linkage are known as Tergitol 15--S--X.TM. and Triton CF.TM. (Union Carbide, Danbury, Conn.). The general structural formula for these surfactants is as below: EQU R--O--(CH.sub.2 --CH.sub.2 O).sub.n --H
wherein R is a C.sub.8 to C.sub.20 hydrocarbyl group and n is a number having a value from about 3 to 40 or more. Coatings made from compositions containing such a surfactant would be more hydrophilic than a coating made in its absence since the surfactant would remain in the coated film upon drying and not be removed except possibly by copious washing with water. Such surfactants would also be categorized as chemically stable, resisting all but the most severe acid, base or enzymatically catalyzed destructive processes. Loss of such surfactants in the waste streams from treatment baths constitutes a serious environmental problem, particularly when the hydrophobe is polyfluorinated.
Destructible nonionic surfactants are known. It is disclosed in U.S. Pat. No. 2,476,307 that a hydrolyzable silicon-containing compound of the formula: EQU C.sub.18 H.sub.37 Si[O(CH.sub.2 CH.sub.2 O).sub.4 H].sub.3
is soluble in water to give a slightly cloudy solution useful for producing oil-in-water type emulsions that can render textile fiber water-repellent by a process in which the silicon ester hydrolyzes, splitting off the polyglycol radicals, and changing the residue into a polymer of an alkyl-siliconic acid. However, coating compositions containing solely such a silicon-containing compound would not produce an oil-repellent finish on a substrate.
U.S. Pat. No. 4,865,910 teaches the treatment of a glass fiber product with fluoroalkylsilanes of the formula: EQU CF.sub.3 --CH.sub.2 --CH.sub.2 --SiX.sub.3
wherein X represents a hydrolyzable group such as an alkoxy group, including 2-methoxyethoxy. Also taught is that fluoroalkylsilanes of the formulae: ##STR1## lack water solubility and that surface treatment with their methanolic solutions exhibits no effect.
U.S. Pat. Nos. 4,929,666 and 5,006,624 describe water-dispersible, crosslinkable polymeric surfactants having fluorocarbon and ionic moieties that can be cured into tough, solvent resistant, low critical surface tension coatings useful for protective finishes that adhere to most surfaces. Such polymeric surfactants require polyfunctional crosslinkers capable of reacting with the ionic moiety of the surfactant in order to cure.
Conventional methods for providing oil- and water-repellent coatings via aqueous delivery generally utilize a fluorochemical (resin or polymer) dispersed in water containing an external stable surfactant.