Relationship between Shear-Induced Structure and Optical Anisotropy on CPyCl/NaSal Aqueous Solution.

Abstract

An aqueous solution of cetylpyridinium chloride and sodium salicylate, which forms wormlike micelles, shows shear-induced structure changing phenomenon at a certain shear rate. An opaque ring region appears in parallel plate flow cell when this phenomenon takes place. The critical shear rate was calculated by measuring the inner diameter of the opaque ring and the rotation rate of flow cell, and it was 85 s-1 in this case. The opaque ring is blinking at a constant period in steady shear flow. The minimum inner diameter of the ring region is decreased and the blinking frequency becomes higher with increasing shear rate. Three-dimensional information of birefringence, dichroism and orientation angle was measured by a double-beam rheo-optical analyzer. Birefringence changed periodically and it was synchronized with blinking of the opaque ring. The orientation angle of birefringence in shear plane was fluctuating and it was not clearly synchronized with the blinking of the opaque ring. Dichroism measured by shear direction was also fluctuated but mean value was almost zero. On the other hand, dichroism in shear plane was fluctuated with non-zero mean value.