Physicochemical investigations in systems of composition biosurfactant/sodium dodecyl sulfate/water around the critical micelle concentration

Abstract Some results of the investigation of the physicochemical properties of aqueous solutions of the synthetic surfactant sodium dodecyl sulfate (SDS) together with each of the two surfactants obtained from assimilating processes, sophorose lipid or rhamnose lipid, in the concentration range that involves micelle formation, are presented and discussed in this paper. The measurements of the solubilities, surface tensions, conductivities, pH values, and enthalpies of diluted mixtures of these solutions at 25°C were evaluated for this purpose. An improved method using a concentration gradient is proposed for precise conductivity and calorimetric measurements in the now conditions. The mathematical model for the description obtained from these experimental data was additionally developed. The results reveal that the low solubility of glycolipids in water may be considerably improved in the presence of SDS. The observed concentration dependence of all studied properties, suggest that formation of mixed micelles consisting of SDS and glycolipid monomers may occur. This aggregation takes place at a concentration of about one order of magnitude lower than the critical micelle concentration of SDS alone. The surfactant mixtures in solution exhibit non-ideal behaviour.