Effects of added tetramethylammonium chloride on sodium dodecyl sulfate micellar structure: electron scavenging ability of doxylstearic acid spin probes and their reaction with N,N,N',N'-tetramethylbenzidine photogenerated cations studied by electron spin resonance

Abstract

Electron spin resonance (ESR) studies are carried out for a series of chi-doxylstearic acids (chi = 5, 7, 10, 12, and 16) and photoproduced N,N,N'N'-tetramethylbenzidine (TMB) cations in sodium dodecyl sulfate micelles in order to investigate the effects of added tetramethylammonium chloride (TMACl) on the micellar structure at room temperature. It is observed that chi-doxylstearic acids not only act as electron acceptors for electrons produced by photoionization of TMB but also react with TMB cations to produce nonparamagnetic products. chi-Dependences of the reactivities of these two reactions suggest that chi-doxylstearic acids increase their average number of gauche conformations inside the micelles when TMACl is added to the micellar solution. It is concluded that tetramethylammonium cations act as spacers between head groups of surfactant molecules to become more disordered and loosely packed inside the micelles. This confirms previous electron spin echo modulation studies on frozen micellar solutions.