Conductometry and Thermodynamics Study of Metal Dioctylsulfosuccinate in Aqueous Solution

Abstract

The aggregation behavior of metal dioctylsulfosuccinate (MDSS) [Na+, Mg2+, Mn2+, Co2+, and Ni2+] in water has been studied by electrical conductivity (at 303.15 to 323.15 K) and surface tension method (at 303.15 K). Critical micelle concentration (CMCs), degree of counterion dissociation (β) evaluated from conductivity data. Using law of mass action, the thermodynamic parameters viz. Gibbs function (), enthalpy (), and entropy () were evaluated. The enthalpy of micellization decreases strongly with increasing temperature. ΔG is always negative (thermodynamically favored process), and slightly temperature and counterion dependent. Gibbs energy and entropy exploit micellization as thermodynamic favorable process. The electrostatic repulsions between ionic head groups, which prevent the aggregation, are progressively screened as the ionic character decreases with the size of counterion. The plots of differential conductivity (dk/dc) T,P , versus the total surfactant concentration enables us to determine the CMC values more precisely than the conventional method. The data are explained in terms of molecular characteristics of surfactants viz. degree of dissociation, polar head group size and counerion.