Formation of a Banded Texture in Solutions of Liquid-Crystalline Polymers 11. Poly(n-Hexylisocyanate) in Toluene

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Abstract
The kinetics of band formation has been followed during the relaxation of anisotropic solutions of poly(n-hexylisocyanate) in toluene previously subjected to a shear rate, for a time ts. There is a threshold at low, or ts, below which bands do not appear (formation time t b→ ∞). Past the threshold, t s decreases with either or t s, and eventually bands are seen immediately after stopping the flow (tb = 0). However, for still larger particularly for the more viscous solutions and when the flowing solution is well oriented, tb may increase again. The results are similar to those already reported for hydroxypropylcellulose in water and support a previous suggestion for the origin of the banded texture.