The Role of Intermolecular Interactions in the Micellization Process of Alkyltrimethyl Ammonium Bromides in Water

Abstract

Abstract The micellization process of model cationic surfactants, alkyltrimethylammonium bromides with different alkyl chain length: dodecyl-(C12TAB), tetradecyl-(C14TAB) and hexadecyl- (C16TAB) has been investigated by the conductivity measurements over the temperature range 298.2 K–313.2 K. Understanding micelle formation requires its complete thermodynamic parameters, which were estimated by applying the proposed alternative derivation of pseudo-phase model. The critical micelle concentration (CMC), standard free Gibbs energy (Δmic G 0), enthalpy (Δmic H 0) and entropy (Δmic S 0) of micellization were analysed as a function of the increase in alkyl chain and temperature. At lower temperatures, the micellization in each case was found to be entropy-driven due to the increase in bulk water entropy. London or dispersion interactions are responsible for the cohesion between the apolar chains in the micelles and increase as the length of chains increases. Δmic H 0 reflects the contribution of London interactions, electrostatic repulsion between head groups and removing the alkyl chains from water (dehydration of CH2 and CH3 groups). As the temperature is increased, less energy is required for dehydration and hence the enthalpy of micellization became more exothermic and its effect more significant. The enthalpy-entropy compensation phenomenon was observed for all studied surfactants.