Dissolution of anionic surfactants. Effect of cations on the change in heat capacity

Abstract

The dissolution of surface-active agents in water usually results in significant heat capacity change, ΔrCp, which is due to water structuring around the nonpolar "tails". For most surfactants, ΔrCp is proportional to the chain length. The heat of dissolution of various salts of anionic surfactants was measured using a reaction calorimeter. The heat capacity change was evaluated from the temperature dependence of the enthalpy. The effect of cations on the ΔrCp of dissolution of fatty and sulphonic acid salts was investigated. All the examined surfactants showed a similar effect; however, the value of ΔrCp was found to be unusually high for copper dodecyl and tetradecyl sulphonates, and this was explained in terms of solid-phase hydration. © Springer-Verlag 1999.