Equillibrium, Dynamic surface properties of alkyl and alkyl ether sulfates and their relation to foaming behaviour

Abstract

Alkyl sulfates and alkyl ether sulfates are widely used anionic surfactants in cleaning products. There have been several studies showing the effect of ethoxylation on the equilibrium surface properties. However, an understanding of the dynamic behaviour at air water interface is required to explain foaming ability of the surfactants. This project is therefore undertaken to infer the effect of ethoxylation on equilibrium as well as dynamic surface tension (DST) and its relation to foaming behaviour of alkyl sulfates Sodium Dodecyl Sulfate (SDS), Primary Alkyl Sulfate (PAS) and alkyl ether sulphate, Sodium Lauryl Ether Sulfate (SLES). The submicellar solutions of SLES showed a low equilibrium and dynamic surface tension compared to both the alkyl sulfates, SDS and PAS. The study revealed an interesting fact that, the micellar solution of SLES is poor in reducing the dynamic surface tension compared to its nonethoxylated counterpart SDS, as a consequence of increased micellar stability. The foamability of submicellar and micellar solutions showed a good correlation with the observed dynamic surface behavior. Addition of NaCl resulted in a reduction in both equilibrium as well as dynamic surface tension. As expected SLES showed an excellent hardness tolerance, as the ethoxyl group binds the Ca2+ ions preventing its interaction with the sulfate head groups.