Investigation of the texture and structural changes in liquid-crystal solutions of poly-γ-benzyl-L-glutamate under the effect of electric fields in a sandwich-type cell

Optical polarization microscopy and low-angle scattering of linearly polarized light have been used to investigate the textural and structural changes in liquid-crystal solutions of poly-γ-benzyl-L-glutamate placed in a sandwich-type cell ('lengthwise' observation geometry) with a thickness in the range of 20 to 200 μm and subjected to the action of electric fields with various frequencies. As distinct from the results obtained previously with a 'transverse' observation geometry, strong wall-boundary effects are observed that prevent the formation of the 'fingerprint' texture in the absence of a field. Other observations include 'chessboard' and 'Swiss-roll' packing of cholesteric domains, the breakdown of π walls as the electric field strength is increased and a simultaneous increase in the proportion of homeotropic texture. At a certain sandwich thickness and field frequency, an unusual accretion of material with homeotropic texture into coarse cells has been observed. As in optical cells, the same sequence of structural rearrangements with an increase in the field has also been observed in the 'sandwich' conical strain, textural transitions, the partial unfolding of the cholesteric domains and electrohydro- dynamic instability.