Temperature dependence of heat capacities of sodium decanoate, sodium dodecanoate, and sodium dodecyl sulphate, in water

Abstract

The enthalpies of solution at very low concentrations of the surfactants sodium decanoate, sodium dodecanoate, and sodium dodecyl sulphate in water were determined from 288.15 to 338.15 K. The heat capacities of dissolution ΔC_p,2^∞ from 293.15 to 333.15 K of these surfactants were derived from enthalpies of solution. The ΔC_p,2^∞values were combined with estimated values of heat capacities C_p,2^∞ of the pure solids and of intrinsic heat capacity C_p,2(in), to obtain the structural heat capacity C_p,2^∞(str) at various temperatures. These results along with the partial molar heat capacities C_p,2^∞ reported in the literature for homologous sodium salts of lower fatty acids provide an interesting insight into the temperature sensitivity of "hydrophobic hydratio".