A comparison study between sodium dodecyl sulfate and sodium dodecyl sulfonate with respect to the thermodynamic properties, micellization, and interaction with poly(ethylene glycol) in aqueous solutions

Abstract

The density, sound velocity, and conductivity measurements were performed on aqueous solutions of sodium dodecyl sulfate (C 12H 25SO 4Na) or sodium dodecyl sulfonate (C 12H 25SO 3Na) in the absence and presence of poly(ethylene glycol) (PEG) at different temperatures. Changes in the apparent molar volumes and isentropic compressibilities upon micellization were derived using a pseudophase-transition approach and the infinite dilution apparent molar properties of the monomer and micellar form of C 12H 25SO 4Na and C 12H 25SO 3Na were determined. Variations of the critical micelle concentrations (CMCs) of both surfactants in the solutions investigated with temperature were obtained from which thermodynamic parameters of micellization were estimated. It was found that at low temperature the micelle formation process is endothermic and therefore, this process must be entropically driven. However, upon increasing the temperature, the enthalpic factor becomes more significant and, at temperatures higher than 303.15 K the micellization is enthalpy driven. The interactions between C 12H 25SO 4Na/C 12H 25SO 3Na and PEG were studied and it was found that sodium alkyl sulfonates were seen to interact more weakly than their sulfate analogues.