A Thermodynamic Study of Lipid–Surfactant Interactions in Non-aqueous Media

Abstract

Interactions between the cationic surfactant cetyltrimethyl ammonium bromide, dimethylsulphoxide and lauric acid, have been studied in detail using volumetric and viscometric techniques. The critical micelle concentration (cmc) values have been determined using two different methods. The experimental data have been correlated against temperature and concentration using standard relations. From the density of the surfactant, the change of the apparent molar volumes at infinite dilution, $$ V_{\phi }^{\text{o}} $$ , apparent molar volumes at the cmc, $$ V_{\phi }^{\text{cmc}} $$ , and apparent molar volumes upon micellization, $$ \Delta V_{\phi }^{\text{m}} $$ , have been calculated. The viscosity data have been analyzed by means of the Jones–Dole equation in the pre-micellar region and the Einstein equation in the post-micellar region. The values of Falkenhagen coefficient and Jones–Dole coefficient thus obtained are used to interpret the solute–solute interactions in the pre-micellar region whereas Einstein’s equation is used to explore solute–solvent interactions in post micellar regions. Transition-state theory was applied to obtain the activation parameters of viscous flow, i.e., Gibbs energy of activation $$ \Delta G^{\text{o*}} $$ , per mole of solvent and solute. Moreover, the enthalpy $$ \Delta H^{\text{o*}} $$ and entropy of activation of viscous flow $$ \Delta S^{\text{o*}} $$ were computed in the pre-micelle regions. The obtained results indicate that the cmc strongly depends on the composition of the mixture. The results have been interpreted in the light of various interactions occurring among the components of the mixtures under the applied experimental conditions.