Determination of critical micellar aggregation numbers of surfactant by steady-state fluorescence probe method

Abstract

The critical micelle concentrations of Cetyltrimethylarnrnonium bromide (CTAB), Sodium laurylsulfonate (C12AS) and the given mixtures at ratio 1/1 were measured by surface tension measurement in aqueous solution at room temperature. By drawing lgc-γ to determine the CMC values are 0.00091mol/L, 0.0089 mol/L and 0.00004 mol/L. The results showed that the CMC of mixed surfactants was lower than the pure surfactants, showing a better synergetic behavior. To determine the micelle aggregation number with the method of a steady state fluorescence quenching, Pyrene was used as probe and Benzophenone as quencher. The concentration of pyrene was fixed in 1×10-5mol/L, and the concentrations of Benzophenone were selected in difference. The results showed that the aggregation number increased linearly with the increasing of CTAB concentration. The micelle aggregation number of C12AS solution which is higher than the series of CMC concentration showed the trend of gradually increase. The micelle aggregation number which increased with the increasing of surfactant concentration of the mixed surfactant system were lower than that of pure C12AS and pure CTAB.