Hysteretic Behavior of a Reversely-Pretilted Weakly-Anchored Large-Pitch Cholesteric and a Finger-Print Embedded Into a Homeotropic Matrix Under Different Sweeping Rates of an AC Voltages

Abstract

The structural transformations of an initially planar Grandjean-like texture with a weak θ-polar anchoring and a reverse pretilt of the liquid crystal at the boundaries are studied under the influence of an AC voltage with a sweeping rate of 0,02 V/sec, 0,2 V/sec and 2 V/sec. At a sweeping rate larger than 1 V/sec, the liquid crystal oscillate with a large dynamic hysteresis between the Grandjean-like and homeotropic orientations passing through a conical deformation. The increase of the voltage at a sweeping rate smaller than 1 V/sec led to a textural hysteresis resulted in Helfrich's instability, a 90° rotation of the helix and a total unwinding. The decrease of the voltage however, caused after a relatively fast dielectric reorientation the formation of domains of Rault-Cladis with a zig-zag form which after relaxation in usual fingers disappeared into the initial Grandjean-like orientation. Dynamic hysteresis was also observed in electricallyexcitated finger-print embedded into a homeotropic matrix-homeotropic pseudonematic phase transformation.

Keywords:

• large-pitch cholesteric
• homeotropic orientation
• planar orientation
• electro-optic behavior
• dynamic hysteresis and textural transformations