Fluorosilicone antifoams

Abstract

AbstractAntifoam compositions for aqueous surfactants are usually emulsions of insoluble oils containing hydrophobic solids. The emulsion allows easy access to the aqueous environment. The oil droplets carry the solid particles to the foam interfaces by spreading, which also contributes to foam rupture. The particles provide a disruptive dewetting surface and may also adsorb the foam stabilizer. This theory requires both oil and solid to have lower surface tension than the foaming surfactant and explains the ineffectiveness of conventional silicone antifoams based on polydimethylsiloxane against silicone and fluorocarbon aqueous surfactants. Some fluorosilicones have lower surface tensions than polydimethylsiloxane and should produce more effective antifoams. To test this idea the liquid surface tensions of a series of fluorosilicone‐containing copolymers were measured. These fluids were formulated into antifoam compounds and emulsions and tested against selected surfactants. Equilibrium and dynamic surface tensions of these test surfactants were also measured. The new antifoams are more effective than conventional silicones against silicone surfactants but are ineffective against fluorosurfactants. The implication of these results on the spreading/dewetting theory is discussed.