FLUORESCENCE-PROBE STUDY OF ANIONIC CATIONIC SURFACTANT SYSTEMS .2. ALKYLSULFONATE ALKYLTRIMETHYLAMMONIUM BROMIDE

Steady state fluorescence and time-resolved fluorescence techniques ha ve been used to study the properties of two kinds of anionic surfactan t systems and four kinds of mixed anionic/cationic surfactant systems. The two anionic surfactant systems are sodium dodecyl sulfate and sod ium dodecylsulfonate (C12As) aqueous solutions. The four alkylsulfonat e/alkyltrimethylammonium bromide systems consist of C12As/cetyltrimeth ylammonium bromide (CTAB), sodium octylsulfonate (C8As)/CTAB, sodium h exadecylsulfonate (C16As)/CTAB and C12As/dodecyltrimethylammonium brom ide (DTAB). We discuss mainly the variation of the micellar aggregatio n number of these systems with the NaCl concentration and temperature. Both the addition of anionic surfactant to cationic surfactant and of cationic surfactant to anionic surfactant result in a large increase in the micellar aggregation number. In addition, by a steady state flu orescence technique, the critical micelle concentration (CMC) for the C8As/CTAB and C12As/DTAB systems and the second CMC for the C12As, C12 As/CTAB and C12As/DTAB systems at which the micelles changed from sphe rical to rod shaped were determined. At the same time, the solubilizat ion position of the fluorescence probe (pyrene) and the polarity of th e probe microenvironment in the mixed anionic/cationic micelles were s tudied.