Threadlike micelles from cetyltrimethylammonium bromide in aqueous sodium naphthalenesulfonate solutions studied by static and dynamic light scattering

Abstract

Dynamic and static light scattering measurements have been made on both dilute and semidilute solutions of the threadlike micelles formed in equimolar mixtures of CTAB and sodium naphthalenesulfonate in aqueous solutions. In dilute solution (1 mM), the first normal mode of the chains (tj) was isolated from the contin decay time spectra as a function of measurement angle. The value of t¡ agreed with that estimated by the free-draining Zimm model. At higher, semidilute concentrations (C > 0.02 M) above which the solutions become viscoelastic, the decay time distribution is bimodal with well-separated components on the time scale. The faster (q2-dependent) component reflects the cooperative motions of the transient network formed through interchain entanglements. The slow (q-independent) component of large amplitude apparently reflects the disruption/coalescence kinetics of the micellar aggregates, which are characterized by a strong positive concentration dependence of the measured relaxation rate (i.e., a relaxation time which decreased with increasing concentration of the CTAB/naphthalenesulfonate complex) and an activation energy of about 84 kJ-mol"1.