Thermochemistry of dissolution of sodium alkylsulfonates

The effect of temperature on the solubility of ionic surfactants was interpreted in terms of standard enthalpy and entropy of dissolution at reference temperature by considering the change in the heat capacity. The significant value of the latter quantity causes the curvature of the function logarithm of equilibrium constant (or solubility) vs. the reciprocal thermodynamic temperature. The solubility data for several sodium n-alkylsulfonates, published by Saito, Moroi, and Matuura, were interpreted by nonlinear regression analysis. It was found that both the enthalpy and entropy of dissolution decrease with the chain length. The heat capacity increases in the course of the dissolution process.