THERMODYNAMICS OF MICELLIZATION OF N-ALKYLPYRIDINIUM CHLORIDES

The effect of temperature on the thermodynamic parameters of micellization of a homologous series of n-alkylpyridinium chlorides has been studied by isothermal microcalorimetry. The decyl, dodecyl and tetradecyl compounds were studied both in water and in 0.1 M NaCl in the temperature range 6-60-degrees-C. Enthalpies and entropies of micellization are strongly temperature dependent whereas there exists only a weak temperature dependence for the standard Gibbs energies. With increasing temperature, the micellization process changes from endothermic to exothermic, indicating the importance of hydrophobic bonding. The transition temperature decreases with increasing chain length; this was interpreted in terms of a relationship between the temperature and the enthalpy per CH2 group. It was concluded by extrapolation that this enthalpy was zero at a temperature of about -12-degrees-C. Enthalpies of micelle formation calculated from the temperature dependence of the CMC compare satisfactorily with those obtained microcalorimetrically.