Structure transitions of mixed micelles in aqueous systems

The conductances of cetylpyridinium chloride (CPyCl), tetradecyltrimethylam monium bromide (TTAB), and their mixtures over the entire mol fraction rang e of CPyCl (x(CPyCl)) were measured in aqueous micellar solutions of non-io nic surfactants (polyoxyethylene tert.-octylphenyl ether, polyoxyethylene s orbitan (20) monolaurate, and polyoxyethylene (80) sorbitan monooleate) con taining 0.25-16% w/w of each additive at 30 degrees C. The conductivity cur ves for CPyCl, TTAB, and their mixtures show a clear break point which subs equently becomes less significant with increasing amount of non-ionic surfa ctant. The break point in each curve represents the structure transition (S T) of non-ionic surfactant micelles upon incorporating the ionic surfactant monomers in order to form the mixed micelles. A variation in the slopes be fore and after the ST reveals that the micelles of the polyoxyethylene tert .-octylphenyl ether also undergo ST.