Surface-chemical study of an aqueous mixture of α-sulfolauric acid salts with cationics

Abstract

The physicochemical properties of an aqueous mixture of α-sulfolauric acid (H 2LS) and its various salts, including sodium α-sulfolaurate (NaHLS), triethanolammonium α-sulfolaurate (TeAHLS) with a cationic surfactant, decyltrimethylammonium bromide (DeTAB), have been investigated. The surface activities of H 2LS and its salts were enhanced greatly in the mixed systems; e.g. for a 1:1 mixed solution, the cmc and γ cmc can be reduced from 1.4 × 10 −2 mol dm −3 and 45 mN m −1 to 5 × 10 −4 mol dm −3 and 24 mN m −1 respectively. The effect of inorganic electrolytes (NaBr and HBr) on the surface activity and the molecular interactions between the two surfactants in the mixed adsorption layer and micelles have been studied systematically. It was found that the phase separation concentrations (PSCs) of the mixed surfactant solutions are greater than the cmcs. For 1:1 NaHLS-DeTAB solution, PCS/cmc=3.2. It is also revealed that, unlike the common anionic-cationic mixture, e.g. C 10H 21SO 4Na-DeTAB, the mixed micellar solution is thermodynamically stable up to 3 × cmc.