The effect of high volume fractions of latex particles on foaming and antifoam action in surfactant solutions

Abstract

Water-Borne coatings usually contain high volume fractions of latex particles together with high concentrations of surfactants. Presence of the latter means that the coatings have an undesirable tendency to foam during dispensing and application. Oil-based antifoams consisting of mixtures of hydrophobic particles and oils are often used to suppress this tendency. The effect of high volume fractions of latex particles on the foam behaviour and antifoam action in solutions of surfactants typically used in water borne coatings is considered. The surfactants were SDS, AOT and Triton X-100 (an ethoxylated octyl phenol). A mixture of hexadecane and hydrophobed silica was used as an antifoam. The effect of latex particles on foam and antifoam behaviour is complex. It can give rise to three effects – depletion of surfactant concentration by adsorption loss, increase in viscosity and stratification stabilisation of thin liquid films by the particles. We show that the first effect appears to dominate in the case of the selected systems. Additional effects due to stabilisation of foam and oil-water-air pseudoemulsion films by latex particles are also found. Antifoam behaviour appears to correlate with pseudoemulsion film stability. Any stabilisation of such films by latex particles is shown to be readily eliminated by the presence of hydrophobed silica particles.