Mayumi Ouchi

Shear-induced structure change and flow-instability in start-up Couette flow of aqueous, wormlike micelle solution

The occurrence of shear-induced structures (SIS) of a wormlike micellar solution is investigated using an aqueous solution of cethyltrimetylammonium bromide (CTAB)/aqueous sodium salicylate (NaSal) with composition CTAB (0.03mol∕L)∕NaSal (0.23mol∕L). A concentric cylinder Couette cell made of transparent glass is used to generate stepwise start-up shear flow. The shear stress and the brightness, which is an index of the transparency of the fliud, are measured simultaneously and the fluid motion is observed by adding tracer particles to the fluid. Measurements of flow birefringence and light intensity of a transmitted laser beam passing parallel to the vorticity axis are also carried out to monitor flow-induced microstructural changes. The transient behavior of the macroscopic properties, i.e., the shear stress and the brightness, are consistent with each other and with the optical microstructural measurements, confirming that the occurrence of the transparent-to-opaque change in the wormlike micelle solut...