Change in Micellar Structure in Surfactant Solution Induced by Periodical Shear Flow

抄録

The present study examined the structural change in micelles induced by surfactant flow in a channel with complex geometry. The channel used in experiments was a slit channel repeating a periodical expansion-contraction in a flow direction. Test fluid is a mixture of CTAB (cetyltrimethylammonium bromide) and NaSal (sodium salicylate) in distilled water and their concentrations are CTAB 0.03mol/l and NaSal 0.12mol/l. In the present experiments, the measurement of pressure loss through the expansion-contraction channel and the flow visualization using a crossed polarizing system were carried out. In the measurement of pressure loss, we found that the abrupt increment of flow resistance appeared in the flow curves. This abrupt increment of flow resistance was related to the structural change in micelles because the increment tendency was similar to the shear thickening property appearing in steady shear viscosity of fluid. However, with respect to the behavior after the occurrence of shear thickening property, the results for the periodic channel were different from the property of shear viscosity. In the flow image at the condition after the increment of flow resistance, we observed the white turbidity of fluid. Because the white turbidity represents flow birefringence caused by the structural change in micelles, we examined the change in retardation in a proportional relationship with birefringence. We found that the change in retardation around the contraction part became remarkable.