SURFACE-CHEMICAL STUDY OF AN AQUEOUS MIXTURE OF ALPHA-SULFOLAURIC ACID SALTS WITH CATIONICS

The physicochemical properties of an aqueous mixture of alpha-sulfolau ric acid (H2LS) and its various salts, including sodium alpha-sulfolau rate (NaHLS), triethanolammonium alpha-sulfolaurate (TeAHLS) with a ca tionic surfactant, decyltrimethylammonium bromide (DeTAB), have been i nvestigated. The surface activities of H2LS and its salts were enhance d greatly in the mixed systems; e.g. for a 1:1 mixed solution, the cmc and gamma(cmc) can be reduced from 1.4 x 10(-2) mol dm(-3) and 45 mN m(-1) to 5 x 10(-4) mol dm(-3) and 24 mN m(-1) respectively. The effec t of inorganic electrolytes (NaBr and HBr) on the surface activity and the molecular interactions between the two surfactants in the mixed a dsorption layer and micelles have been studied systematically. It was found that the phase separation concentrations (PSCs) of the mixed sur factant solutions are greater than the cmcs. For 1:1 NaHLS-DeTAB solut ion, PCS/cmc=3.2. It is also revealed that, unlike the common anionic- cationic mixture, e.g. C10H21SO4Na-DeTAB, the mixed micellar solution is thermodynamically stable up to 3 x cmc. (C) 1998 Elsevier Science B .V.