Striking differences between alkyl sulfate and alkyl sulfonate when mixed with cationic surfactants

Abstract

The properties of alkyl sulfate and alkyl sulfonate are similar except for their Krafft points. However, alkyl sulfate and alkyl sulfonate behave quite differently when they are mixed with cationic surfactants and show some totally unexpected results. In this work sodium alkyl sulfate (CnH2n+1SO4Na,CnSO4)–alkyl quaternary ammonium bromide [CnH2n+1N(CmH2m+1)3Br, CnN, m=1–4] mixtures and sodium alkyl sulfonate (CnH2n+1SO3Na, CnSO3)–CnN mixtures were studied. It was found that, in contrast to the single surfactants, CnSO3–CnN mixtures were much more soluble than CnSO4–CnN mixtures. Besides, the two kinds of catanionic surfactant mixtures were quite different in their phase behavior and aggregate properties. The results were interpreted in terms of the interactions between surfactant molecules, which were very different in the two kinds of mixed systems owing to the distinction between alkyl sulfate and alkyl sulfonate in the molecular charge distribution.