Property of Shear Viscosity of Organic Substance Added Surfactant Solution and Effect of Additives on Structural Transformation

We investigated rheological properties of surfactant solutions including a small amount of organic additives, and discussed the effect of additives on the structural transformation of micelles. Test fluids used were mixtures of an aqueous solution of CTAB/NaSal and 2,2,4-trimethylpentane (isooctane). The ratio of NaSal to CTAB (0.03 mol/l) was 7.7 and the concentrations of isooctane to the surfactant solution were 0.01 wt% and 0.1 wt%. In measurements of linear viscoelasticity, it was found that the dynamical property of fluids including additives was described by a single mode Maxwell model. However, the relaxation time decreased with the increase in isooctane concentration. Such change in relaxation time was related to the solubilization of organic additives into micelles, which weakened the mechanical strength of micelles. Furthermore, viscosity curves showed that the structural transformation from a wormlike micelle to a spherical one occurred. In experiments of small angle light scattering in shear flow, the comparison of scattering patterns between a fluid with additives and that without additives captured differences due to the structural transformation. In addition, it was found that the isooctane in solution took a spherical structure, which distributed in a wide range of diameter.