Effect of acetonitrile on the micellization and thermodynamic parameters of tetradecyltrimethylammonium bromide: Conductometric and fluorimetric studies

Micellization and related thermodynamic parameters of a conventional cationic surfactant tetradecyltrimethylammonium bromide (TTAB) in various compositions of water-acetonitrile (W-AN) mixed media have been studied at four temperatures ranging between 298.15 K and 323.15 K. We employed conductometric and fluorimetric experiments to obtain the parameters like critical micelle concentration (cmc), degree of counterion dissociation (α), and average aggregation number (Nagg). Assuming mass-action model for micelle formation, various thermodynamic parameters were also estimated from the temperature dependence of cmc values. The inclusion of AN caused an increase in cmc of TTAB and a decrease in Nagg of micelles whereas the thermodynamic analysis shows that, although the micellization is not favorable compared to pure water, the process is spontaneous and exothermic.