Rheo-optic behavior of wormlike micelles under a shear-induced structure formational condition - Verification of stress-optic rule by full component measurement of refractive index tensor

Abstract

An aqueous cationic surfactant solution, CTAB/NaSal, forms wormlike micelles and shows viscoelastic properties. It also shows shear-induced structure change at shear rates higher than 4 s-1. Full components of the refractive index tensor under step shear flow were measured by using double-beam rheo-optical analyzer in addition of shear stress and first normal stress difference measurement. Each component of the refractive index tensor is proportional to the corresponding component of the stress tensor when shear rate is lower than 6 s-1. However, a stress-optical coefficient, C, suddenly decreases above 4 s-1. At shear rates between 4 to 6 s-1, the stress-optic rule holds, but micellar structure might change.