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.