N-ALKYLTRIMETHYLAMMONIUM BROMIDES IN A BUFFERED MEDIUM - A THERMODYNAMIC INVESTIGATION (CORRECTED VERSION OF PC241)

The critical micellar concentrations (c(c.m)) of n-alkyltrimethylammon ium bromides of alkyl-chain length 10, 12, and 14 carbon atoms in glyc ine buffer solutions at pH = 10.0 have been determined at the temperat ures T = (288.15, 293.15, 298.15, 303.15, and 308.15) K by the electri cal-conductivity method. From the conductivities the degrees beta of t he counterion binding have been calculated. It is shown that ln(c(c.m) /c-degrees) decreases linearly with increase in the length of alkyl ch ain and that plots of the c(c.m) against temperature pass through mini ma between T = 293.15 K and 303.15 K. Beta increases with increasing a lkyl-chain length and decrease with temperature. To derive thermodynam ic quantities for micellization from temperature, the classical-equili brium model has been applied. Only small differences in the standard m olar Gibbs free energies of micellization over the temperature range s tudied have been observed. The enthalpy of micellization is strongly d ependent on the temperature.