Effect of Hydrophobic Chain Length of Surfactants on Enthalpy−Entropy Compensation of Micellization

Abstract

It is well-known that there exists a minimum critical micelle concentration (cmc) in the cmc−temperature curve. It is found that the temperature of minimum cmc, Tmin, for both nonionic and ionic surfactants increases as the hydrophobicity of surfactants decreases. The temperature dependence of cmc is used to calculate the enthalpies and entropies of micelle formation for six different homologous series of surfactants. The enthalpy−entropy compensation plot exhibits an excellent linearity. It is found that all the compensation lines for surfactants in a homologous series are parallel to one another and the intercept of these compensation lines is a linear function of the hydrophobic chain length of surfactants.