Effect of propylene carbonate on the adsorption and aggregation of surfactants

Surface tension of TX-100 and AOT was measured at 25 °C in water + propylene carbonate (PC) media containing 5, 10, 15, and 18 wt.% PC. Micellization does not take place in neat PC. Critical micelle concentration (cmc) of TX-100 increases with increase in percentage of PC, while that of AOT passes through a minimum around 5% PC. cmc values of AOT in 15% and 18% PC were obtained from the fluorescence emission spectra of pyrene, but not from surface tension data. Counter ion binding constant of AOT has two values in 5% PC as in water, whereas it has single value in mixed solvents containing 10% or more of PC. With increase in surfactant concentration, variation of aggregation numbers of TX-100 and AOT show opposite trends. The recently reported solvophobicity index works in the present system also.