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

The density, sound velocity, and conductivity measurements were performed on aqueous solutions of sodium dodecyl sulfate (C12H25SO4Na) or sodium dodecyl sulfonate (C12H25SO3Na) 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 C12H25SO4Na and C12H25SO3Na 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 C12H25SO4Na/C12H25SO3Na and PEG were studied and it was found that sodium alkyl sulfonates were seen to interact more weakly than their sulfate analogues.

Apparent molar volume against molality: ○, ●, and △, respectively in water, (1 and 4) wt% PEG solution at 293.15 K; ×, △, and ♢, respectively in water, (1 and 4) wt% PEG solution at 313.15 K.Figure optionsDownload as PowerPoint slideResearch highlights
► C12H25SO3Na(SDSn) was seen to interact with PEG more weakly than C12H25SO4Na(SDS).
► The constraints on molecular mobility of SDS micelles are larger than those of SDSn.
► Entropy change on micellization for SDSn is larger than those for SDS.
► Micelle formation of SDS is less endothermic and more spontaneous than that of SDSn.
► Micelles of SDS have smaller aggregation number than that of SDSn.