Thermodynamic and interfacial properties of binary cationic mixed systems

The critical micelle concentration of a binary mixture of C12–C16 triphenylphosphonium bromides with decyltrimethylammonium bromide was determined as a function of temperature employing conductometric titration to evaluate the thermodynamic properties of self-assembly. Using surface tensiometry, the thermodynamics of adsorption, surface excess, and the minimum area occupied by surfactant molecules were also evaluated. Results were analyzed using regular solution theory (RST) to obtain the composition of the mixed micelles and the interaction parameter, βm, to evaluate the type and strength of interactions of surfactants in the mixed micelle. Activity coefficients and excess free energy of mixing were also determined.