RHEOLOGY OF REGION-I FLOW IN A LYOTROPIC LIQUID-CRYSTAL POLYMER - THE EFFECTS OF DEFECT TEXTURE

A thorough rheological investigation into the region I flow of liquid-crystalline hydroxypropylcellulose in water is reported. At low shear rates a region of shear thinning with a power-law exponent 1/2 is observed over two decades in shear rate. Anomalous transient behavior is seen for applied stresses below the critical stress at the region I-II turnover such that the strain required to reach steady state increases as stress decreases. Recoil measurements show large recoverable strain and similar pseudostrain scaling in both regions I and II. The activation energy for the viscosity is also the same in regions I and II. This rheology combined with in situ flow-small-angle light scattering measurements of the defect texture size show the qualitative and quantitative accuracy of the defect texture stress balance previously proposed to explain region I flow.