On the association between poly(vinyl alcohol) and sodium dodecyl sulfate and its effect on liquid-liquid interfacial tension: A mathematical model

Association between poly(vinyl alcohol-co-vinyl acetate) copolymer (PVA) and sodium dodecyl sulfate (SDS) was studied experimentally and theoretically. It was found that, for the ethyl acetate-aqueous phase interface in which PVA was previously adsorbed, the interfacial tension (gamma) increases abruptly to a maximum and then exhibits a relatively mild decay with the addition of SDS to the aqueous phase. The theoretical results indicate that vinyl acetate (VAc) segments determine gamma. However, for relatively low concentrations of SDS (C-SDS), this latter plays a major role because through its association with the VAc segments it modulates the extent to which PVA is adsorbed at the interface, indirectly determining the value of gamma. As C-SDS approaches to the CMC value for SDS, its influence on gamma decreases because SDS tends to self-assembly rather than associates with VAc. These model predictions are consistent with experimental findings reported in the literature.