Thermodynamic parameters of clouding phenomenon in nonionic surfactants: The effect of the electrolytes

Abstract

Abstract In this study, the thermodynamics of the cloud point (CP) of the two non-ionic surfactants, polyoxyethylene (40) iso octylphenyl ether, (TX-405) and polyoxyethylene (23) lauryl ether, Brij-35 were investigated in different electrolyte concentrations. In the measurements of cloud point temperatures, UV–visible spectrophotometer was used instead of visual observation. Li 2 SO 4 , Na 2 SO 4 , KNO 3 , K 2 SO 4 , K 3 PO 4 and (NH 4 ) 2 SO 4 were used as electrolytes. Thermodynamic parameters were calculated from cloud point values of nonionic surfactant-electrolyte mixtures. The CP values in the presence of KNO 3 were obtained by an extrapolation of the straight line. The results of the energetics of clouding showed that the standard Gibbs free energy ( ΔG CP o ) was positive but the enthalpy ( ΔH CP o ) and the entropy ( ΔS CP o ) were negative in all cases. Furthermore, the enthalpy–entropy compensation relationship was estimated and the compensation temperature values (T c ) values were found as 389.70 K and 391.19 K for TX-405 and Brij-35, respectively.