EFFECT OF TEMPERATURE AND ALKYL CHAIN-LENGTH ON THE MICELLAR PROPERTIES OF N-ALKYLTRIMETHYLAMMONIUM BROMIDES IN A LOW PH MEDIUM

The critical micelle concentrations (CMC) of n-alkyltrime-thylammonium 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 temperat ures of 15, 20, 25, 30, and 35 degrees C have been determined by the e lectrical conductivity method. From the conductivity data the degrees of dissociation of micelles (beta) have been calculated. The variation of the CMC with temperature is a second-order polynomial. beta decrea ses with increasing alkyl chain length and is practically constant wit h temperature. To obtain the thermodynamics quantities of micellizatio n, the equilibrium model has been applied. Only small differences have been observed in the standard molar Gibbs free energies of micellizat ion over the temperature range studied, these being the variation with the alkyl chain length in a linear function. The enthalpy of micelliz ation is strongly dependent on the temperature. In the temperature ran ge studied the London dispersions are predominant between approximatel y 25 and 35 degrees C and hydrophobic interactions are predominant in the load range. (C) 1995 Academic Press, Inc.