An aqueous anionic/nonionic surfactant two-phase system in the presence of salt. 1. Rheological behavior and microstructure

Abstract

Aqueous binary surfactant solutions, based on the cloud point phenomenon, have been utilized to design efficient extraction of a variety of substances. In this study, the effect of the anionic surfactant sodium dodecyl sulfate (SDS) on the clouding behaviour of aqueous nonionic surfactant solutions of Triton X-114 (TX-114), in the presence of 100 mM sodium chloride (NaCl), has been studied as a function of temperature by means of turbidity, dynamic light scattering (DLS), and rheo-small angle light scattering (Rheo-SALS). It is found that the addition of 2 mM SDS lowers the phase separation temperature of the surfactant solution by about 2 °C. The hydrodynamic radius of the surfactant aggregates increases with increase of temperature and SDS concentration. The change in microstructure of the surfactant aggregates at different temperature and SDS concentrations is also reflected by the characteristic length and aspect ratio extracted from their SALS patterns, which range from 269 to 623 nm and from 1.01 to 1.40, respectively. The increasing characteristic length and aspect ratio with SDS concentration indicate the growth of the mixed surfactant aggregates is in the flow direction and these elongated aggregates can align under shear.