Thermodynamics of the micellization process of carboxylates: A conductivity study

The micellization behaviour of the long-chain carboxylates: sodium octanoate (NaC8), sodium decanoate (NaC10), potassium decanoate (KC10), caesium decanoate (CsC10) and sodium dodecanoate (NaC12) in aqueous solutions were studied using electrical conductivity measurements between the temperatures (278.15 and 328.15) K. By using the pseudo-phase separation model and Gibbs-Helmholtz equation, the thermodynamic parameters for the micellization process were obtained from the temperature dependence of the critical micelle concentration, CMC, and the degree of micelle ionisation, beta. The heat capacity of micellization, Delta(mic)c(p)(o), estimated from the temperature dependence of enthalpy of micellization, Delta H-mic(o), were correlated with the size of the non-polar accessible surface area of the solvent, which is removed from contact with water during micellization. In all systems investigated, results suggest that the micelle core is still in contact with water molecules. (C) 2014 Elsevier Ltd. All rights reserved.