Predicting conditions for intermediate phase formation in surfactant systems

Abstract

For a pure surfactant below its cloud point, only the location of the limiting tie-line between L ₁ and L ₂ regions is needed to predict with diffusion path theory whether an intermediate phase such as a liquid crystal or microemulsion forms when an aqueous solution of the surfactant is brought into contact with a pure oil. A critical surfactant concentration should exist above which intermedaite phase formation occurs. Experiments for anionic and nonionic surfactants with pure polar oils are consistent with this prediction. In view of results presented previously, removal of pure oils from polyester/cotton fabric during washing processes should improve significantly when intermediate phasews develop. If the surfactant is above its cloud point, at least one intermediated phase forms. In this case the criterion for improved detergency is that water, which solubilizes little oil, not be the only intermediate phase. An approximate method for predicting when such behavior will occur is presented. The results seem generally consistent with available experimental observations.