Effects of Electrolytes on Micellar and Surface Properties of Some Monomeric Surfactants

Micellar and surface properties of cationic surfactants, that is, cetyldiethylethanolammonium bromide (CDEEABr), cetyldimethylethanolammonium bromide (CDMEABr), cetyltrimethylammonium bromide (CTAB), and tetradecyldiethylethanolammonium bromide (TDEEABr) in the presence of sodium halide (NaCl, NaBr, and NaI) have been investigated by conductivity and surface tension measurements at 300 K. The critical, micelle concentration (cmc) and interfacial parameters, such as the maximum surface excess (Gamma(max)), minimum area per molecule (A(min)) and surface pressure at the cmc (pi(cmc)) were computed from the surface tension data. The effects of chain length of cationic surfactants in absence and presence of salts have also been studied. The cmc and degree of micellar ionization (alpha) values were found to decrease with an increase concentration of salts and values decrease in the order NaCl <NaBr <NaI. Thermodynamic parameters, standard Gibbs free energy of micellization (Delta G degrees(m)) and adsorption at air/water interfaces (Delta G degrees(ads)) were also evaluated.