Micellization and catalytic activity of the cetyltrimethylammonium bromide–Brij 97–water mixed micellar system

Abstract

Surface tension measurements and the kinetic study of the basic hydrolysis of ethyl p-nitrophenyl chloromethyl phosphonate were used to examine the structural behavior and catalytic activity of the cethyltrimethylammonium bromide (CTAB)–polyoxyethylene (10) oleyl ether, C 18H 35(OCH 2CH 2) 10OH (Brij 97)–water mixed micellar system. Application of the regular solution model to the experimental data yields the value of the interaction parameter β as −4.6, which indicates an attractive interaction of the surfactants in the mixed micelle and reflects synergistic solution behavior of the mixture. The mixed micellar composition is found to be enriched in the surfactant with the lower critical micelle concentration (cmc). In the kinetic study a nonmonotonic change in the pseudo-first-order rate constant of basic hydrolysis of the substrate is observed with increasing mole fraction of nonionic surfactant. The pseudophase micellar model reveals that the concentration factor mainly contributes to the catalytic effect, while the microenvironmental factor plays a negative role.