Journal of Chemical Thermodynamics, Vol.77, 54-62, 2014
Thermodynamic analysis of unimer-micelle and sphere-to-rod micellar transitions of aqueous solutions of sodium dodecylbenzenesulfonate
Temperature dependence of specific conductivity of sodium dodecylbenzenesulfonate (NaDBS) aqueous solutions was analyzed. Two breaks on the plot appeared for all temperature, which suggest two micellar transitions. This has been corroborated by surface tension measurements. The first transition concentration occurs at the critical micelle concentration (CMC), whilst the second critical concentration (so-called transition micellar concentration, TMC) is due to a sphere-to-rod micelles transition. The dependence of CMC and TMC on the temperature allows the computation of the corresponding thermodynamic functions: Gibbs free energy, enthalpy and entropy changes. For the CMC, enthalpy and entropy increments were found that decrease with the temperature values. However, an anomalous behavior was obtained for the TMC, where both Delta S-0 and Delta H-0 values raised with the temperature increase. However, for both transitions, an (enthalpy + entropy) compensation is observed. These results will be compared with similar systems reported in the literature. (C) 2014 Elsevier Ltd. All rights reserved.
Keywords:Sodium dodecylbenzenesulfonate;Electrical conductivity;Critical micelle concentration;Transition micellar concentration;Sphere-to-rod transition;Micellization thermodynamics