Small-angle light scattering of polymer liquid crystals under shear flow

Abstract

We presented some experimental results on flow small-angle light scattering (‘‘flow SALS’’) of lyotropic polymer liquid crystals which involved real-time, in situ, and simultaneous measurements of mechanical properties and small-angle light scattering (SALS) of a complex structured fluid. The flow-SALS studies were conducted under steady-state Couette flow and during relaxation process occurring after the cessation of the steady-state shear flow. We found the following universal behavior on the structure and properties for two kinds of the liquid crystal systems, i.e., poly(γ-benzyl L-glutamate) in m-cresol and hydroxypropyl cellulose in water. (i) Upon increasing shear rate γ̇, the ‘‘polydomain’’ structure gradually tends to be transformed to the essentially ‘‘monodomain’’ texture through annihilation of the disclinations. On the top of this general tendency, we found more specific characteristic of the fluid systems with γ̇, (ii) at γ̇<γ̇c, a critical shear rate above which a remarkable shear thinning occurs, the disclinations are more or less uniformly distributed in space, while at γ̇>γ̇c the disclinations are localized into domains and dispersed in the more or less uniform medium with a high degree of orientation, (iii) the relaxation after cessation of the steady state shear depends on its γ̇ before the cessation and is quite different below and above γ̇c, and (iv) the cessation from γ̇>γ̇c involves formation of the ‘‘band texture’’ during the relaxation process of the fluids.