Effect of Hydrotropes on the Aqueous Solution Behavior of Surfactants

摘要

Aqueous solutions of surfactants-cationic:tetradecyltrimethylammonium bromide(C_14TABr);anionic:sodium dodecyl sulfate(SDS);and nonionic:polyoxyethylene t-octylphenol(trade name Triton X-102,also called OPE-8)-in the presence of three hydrotropes,viz.,sodium xylene sul-fonate,sodium p-toluene sulfonate,and sodium chloroben-zene sulfonate,were examined by measuring surface tension,viscosity,and cloud points for the nonionic surfactant.The results show a marked decrease in the critical micelle concentration with increase in hydrotrope concentration for C_14TABr,a marginal decrease for SDS,and very little change for OPE-8 up to 0.1 M hydrotrope.The viscosity of cationic surfactant solutions showed a remarkable increase in the presence of trace amounts of hydrotropes(up to 15 mM).In contrast,the SDS solution showed only a slight increase in viscosity at high hydrotrope concentration(150 mM),and the viscosity of the OPE-8 solution remained constant.The cloud point of OPE-8 increased in the presence of hydrotropes,unlike its behavior with the simple salt NaCI.The strong dependence of the solution behavior of cationic surfactants on the presence of hydrotropes is discussed in terms of electrostatic interaction.