Effect of Temperature and Alkyl Chain Length on the Micellar Properties of n-Alkyltrimethylammonium Bromides in a Low pH Medium

Abstract

The critical micelle concentrations (CMC) of n-alkyltrimethylammonium bromides of alkyl chain length 10, 12, and 14 carbon atoms in glycine buffer solutions of pH 3.2 and ionic strength 0.0062, at the temperatures of 15, 20, 25, 30, and 35°C have been determined by the electrical conductivity method. From the conductivity data the degrees of dissociation of micelles (β) have been calculated. The variation of the CMC with temperature is a second-order polynomial. β decreases with increasing alkyl chain length and is practically constant with temperature. To obtain the thermodynamics quantities of micellization, the equilibrium model has been applied. Only small differences have been observed in the standard molar Gibbs free energies of micellization over the temperature range studied, these being the variation with the alkyl chain length in a linear function. The enthalpy of micellization is strongly dependent on the temperature. In the temperature range studied the London dispersions are predominant between approximately 25 and 35°C and hydrophobic interactions are predominant in the load range.