Characterisation of aqueous solutions of ionic surface active agents by conductometry

Abstract

Conductometry data were analysed to determine some equilibrium properties of sodium decylsulphonate aqueous solution. Temperature dependence of conductivity above solubility and below Krafft temperature enabled a determination of the enthalpy of solid phase dissolution. At 15 °C Δ _r H=8.0 kJ mol^-1>which agrees well with calorimetry (8.3 kJ mol^-1>). Increase of enthalpy with temperature is due to the heat capacity change, being 850 J K^-1> mol^-1>. Conductivity data above the Krafft temperature enabled estimation of the degree of association of counterions with charged heads of surfactant chains comprising micelles, as well as the corresponding equilibrium constant. The latter slightly decreases with surfactant concentration which is due to decrease in electrostatic potential affecting the state of associated counterions.