Study on the phase behavior of sodium lauroyl methyltaurate mediated by Ca2+
The effects of high-valent inorganic salts on the surface activity and phase behavior of anionic surfactant sodium lauroyl methyl taurate(or sodium methyl lauroyl taurate,SMLT)were studied.The effects of Ca2+ concentration on the surface tension of SMLT solution and the effects of different SMLT/Ca2+ molar ratios on the phase behavior of SMLT in water were investigated.The results showed that the addition of an appropriate amount of Ca2+ had significant impact on the surface activity.When the Ca2+ concentration was increased from 0 to 0.1 mol/L,the cmc decreased from 8.0×10-3 mol/L to 8.0×10-4 mol/L,and the γcmc decreased from 36.00 mN/m to 31.45 mN/m.Meanwhile,by adding Ca2+ to the SMLT solution,the binary phase diagram of the SMLT/water system showed phase regions of micellar solution region,wormlike micelle region,hexagonal liquid crystal region,lamellar liquid crystal region,and micelle-crystal region.The original aqueous two-phase region disappeared,and the micelle-crystal region became larger.When examining the effect of Ca2+ concentration on the viscosity of SMLT solution,it was found that,with a molar ratio of SMLT/Ca2+ of 1,the viscosity was significantly increased,while at a molar ratio of 0.6,solid precipitated from the solution.An SMLT solution at mass fraction of 20%was selected for measurement of rheological performance.According to the rheological curve of the sample,a phenomenon of shear thinning was observed,and the formation of wormlike micelles was observed by cryogenic transmission electron microscopy.
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