Formation of a Banded Texture in Solutions of Liquid Crystalline Polymers: 1. Hydroxypropylcellulose in H₂O

Abstract

Abstract The formation of a banded texture was investigated for sheared anisotropic solutions of hydroxypropylcellulose (HPC) in H2O. A cone and plate rheometer made of highly polished glass allowed the exploration of the shear rate (γ) range between 0.1 and 150 sec−1 and the study of the effect of shear time ts. Texture, monitored with a video-camera, appeared after a time tb following cessation of shear. tb is usually a decreasing function of γ and ts. In most cases a precursor banded texture precedes the banded texture, and tb attains zero at high enough γ or ts. However, when a particularly good orientation of the flowing solution is achieved, the precursor texture is not observed, tb is finite, and the bands are particularly well formed. We speculate that bands are the normal relaxation mode for well oriented solution. For less oriented solutions flow instability may lead to bands even during flow.