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Flow property, which is expressed by the relation between wall shear stress and apparent shear rate, is examined in the flows of surfactant solutions through various capillaries. Furthermore, small angle light scattering (SALS) experiments are carried out in the flow through a slit cell. In the present experiments, aqueous solutions of Cetyltrimethylammonium bromide (CTAB) and Sodium Salicylate (NaSal) are used. The flow curve has a break point and its slope below the bending point significantly depends on the ratio of salt concentration C S to surfactant concentration C D . From the experiments on the effect of capillary diameter, it is found that eqimolar solution for C D = 0.03M exhibits a remarkable diameter dependence below the break point while the solution for C D = 0.03M and C S /C D = 7.7 exhibits a diameter dependence only in a narrow region at intermediate shear rates. In the SALS experiments the butterfly pattern is observed for C S /C D =1 and the four-fold symmetry pattern for C S /C D = 7.7. The characteristic scattering pattern is destroyed just after the startup of the flow at high shear rates where the flow curves overlaps regardless of salt concentration and length and diameter of capillary. This fact suggests that micellar network structures are broken at the high shear rates.

Flows of wormlike micellar solutions in an axisymmetric capillary channel were studied both numerically and experimentally. In the experimental study, velocity distribution measurements with a particle tracking velocimetry (PTV) were carried out using an aqueous solution of 0.03 mol/1 CTAB and 0.06 mol/1 NaSal as a test fluid. The velocity profile showed a plug-like shape and had infiection points where the velocity gradient rapidly changed. High shear rate regions near the channel walls spread with increasing the average velocity. In the numerical analysis, startup fiows of the CTAB/NaSal solution were computed using a modified Bautista-Manero model as a constitutive equation. Startup flows at a constant average velocity C/or at a constant average pressure gradient -A were numerically simulated. The numerical predictions of velocity profile at steady state agreed with corresponding experimental data. In the constant-[/case, the velocity profile changes from Newton-like to plug-like with time. The infiection points in velocity profile appeared and moved towards the center-side with time. Temporal changes in both velocity gradient and fluidity suggested that the behavior in velocity related the shear-rate-jump property of wormlike micellar solution. In the constant-A case, the region of high shear rate and fiuidity did not spread with time and their profiles temporally changed within this region.

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