Phase Diagrams, Viscous Properties And Application On Extraction Of Mixed Cationic And Anionic Surfactant Systems

Three-dimensional phase diagram, phase behavior and viscous properties of the mixed cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfonate (AS) systems were investigated, and TEM micrographs of some representative systems were also given in order to explain their rheological behavior. Meanwhile, the extraction effect of the aqueous two-phase systems formed by the oppositely charged surfactants on the active component emodin of Chinese rhubarb was explored preliminarily.CTAB/AS/H₂O system is actually a five components system, i.e., CTAB, AS, NaBr, complex salt CTAAS formed by oppositely charged surfactant ion pair and water. The pseudo-ternary phase diagrams have been drawn based on the experimental results. The phase behavior, the formation region of the aqueous two-phase systems and the corresponding properties of the mixed system have been studied. The overall phase diagram has been plotted based on the phase behavior investigation on the many specially chosen planes in the three-dimensional space. The experimental results indicated that certain concentration and molar ratio conditions were required for the formation of the aqueous two-phase systems. The formation of the aqueous two-phase systems was not only observed in the conventional mixing plane, but also the extension of the aqueous two-phase regions could be observed in the three-dimensional space.The shear viscosities of the mixed systems were measured with the cone and plate viscometer of NXE-1B type. The typical rheological phenomena of the systems at isotropic single-phase region with AS in excess are as follows: at a constant x_T, when the molar ratio of CTAB to (CTAB+AS) MR_{CTAB/(CTAB+AS)} increases, the rheological behaviors of the systems usually changes from Newtonian fluids to antithixotropic fluids first, and then to complex thixotropic fluids, and finally to thixotropic fluids. The changes of the rheological behaviors for the systems at the isotropic single-phase region with CTAB in excess are similar to the above phenomena as MR_{CTAB/(CTAB+AS)} decreases. At either isotropic single-phase region, under certain x_T, there exists one shear viscosity maximum peak. As x_T increases, the value of the shear viscosity maximum peak increases. Addition of salt resulted to obvious increase of the value of the shear viscosity maximum peak, and meanwhile the shear viscosity maximum peak shifted to the position far from the equimolar ratio of CTAB and AS. The salt effect on the rheological properties of the mixed systems in the isotropic single-phase region with cationic surfactant or anionic surfactant in excess was mainly dependent on the inorganic anions or cations, respectively. The rheological behaviors of the isotropic single-phase systems around the shear viscosity peak and those of lamellar liquid crystalline systems are complicated. Total surfactant concentration, molar ratio, shear rates and shear time all have influence on the shear viscosities of these systems. The differences observed in rheological behavior may be related to their microstructure differences. Experimental results illustrate that both the isotropic single-phase systems and lamellar liquid crystalline systems located at position very close to the boundaries of the aqueous two-phase systems, as well as the coexisted phases in aqueous two-phase systems are not very viscous. when x_T≤0.005, their shear viscosities are usually several to dozens mPa·s.The extraction conditions of the aqueous two-phase CTAB/AS/H₂O systems on the effective component emodin of Chinese rhubarb were explored preliminarily. The investigation indicated that the absorbances of the emodin in the mixed systems were dependent on the time and temperature which the systems were kept at constant temperature. The extraction efficiency of the aqueous two-phase system with cationic surfactant in excess (ATPS-C) is high, and about 98% of the emodin was extracted to the concentrated top phase of the ATPS-C.