“Bands” and “Torsads” Textures in Films and Threads of Hydroxypropyl Cellulose

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Abstract
The present paper deals with films and threads of a mesomorphic cholesteric polymer: the hydroxypropyl cellulose. The steady flow behaviour and the shear induced textures (observed by optical microscopy under crossed polars) of films of lyotropic solutions of this polymer have been studied. A detailed analysis of the banded structures, of either the sheared solutions or the dried films obtained by solvent evaporation, is reported. We point out the existence of transverse striated patterns—“torsads”—superposed on the main banded structures, which are associated with the rewinding of the cholesteric structure following the cessation of the shear stress. The torsads, also observed in some threads, originate from the same relaxation phenomena and are discussed in the last part of the paper.

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