Thermodynamics of Micellization of n-Alkyltriphenylphosphonium Bromides: A Conductometric Study

Abstract

The electrical conductivity of aqueous solutions of decyl- (C10), dodecyl- (C12), tetradecyl- (C14) and hexadecyl- (C16) triphenylphosphonium bromides (TPPBr) was measured at various temperatures. From the conductivity data the critical micelle concentration cmc, and the effective degree of counter-ion binding β, were obtained at various temperatures using a simple non-linear function obtained by direct integration of a Boltzmann-type sigmoidal function. The thermodynamic parameters om G i„ , om H i„ and om i„S were estimated from the temperature dependence of the equilibrium constants for the micellization of each surfactant using the phase separation model. The stability of the micellization process for these surfactants is both enthalpy and entropy controlled. The resulting om H i„ and om T i„S plots showed significant correlation, an indication of enthalpy-entropy compensation in the micellization process. The intrinsic enthalpy of micellization i„H* varies linearly with the number of carbon atoms in the chain length of the surfactants