THERMODYNAMIC PROPERTIES OF AQUEOUS-SOLUTIONS OF PERFLUORINATED IONICSURFACTANTS

The enthalpies of dissolution of perfluorooctanoic acid, a perfluoropo lyether carboxylic acid and their sodium salts were measured as a func tion of temperature. The heat capacity changes (Delta C-p) were obtain ed from the slope of enthalpy vs. temperature plot. The values of Delt a C-p for perfluorooctanoic acid and its sodium salt are higher than t hose of the corresponding hydrogenated compounds and are accompanied b y lower critical micellization concentrations. The finding is explaine d on the basis of the higher hydrophobicity of perfluorinated compound s. Perfluoropolyether carboxylic acid and its sodium salt showed relat ively lower Delta C-p values which may be due to the branching or the presence of oxygen in the chain. Measurements of the heat capacity cha nge serve also for the explanation of the temperature dependency of th e solubility of surfactants.