The mechanism of shear induced structural changes in liquid crystals—cholesteric-polymer solutions

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Abstract
The reflectance spectra and rheological properties for a cholesteric liquid crystal‐polyisobutylene solution, have been obtained as a function of mechanical shear. The optical data are explained in terms of a layered structure consisting of tilted and untilted helical Grandjean texture and a dynamic focal‐conic texture. At low shear rates < 1.72 sec−1, this system behaves optically and rheologically as a normal mixed cholesteric system. At greater shear rates, the structural reinforcing properties of the polyisobutylene cause optical and rheological behavior different from that observed in mixed cholesteric and cholesteric‐nematic mixtures. The most striking effect of the polyisobutylene is its facility to disrupt the shear induced focal‐conic component, causing relaxation to the Grandjean texture in a way that is similar to raising the temperature or releasing the surface constraints on the system.