Electric Field Induced Relaxation Processes in Unwinding Helical Texture of Ferroelectric Liquid Crystals

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Abstract
Under the influence of electric field, helical texture of ferroelectric liquid crystals tends to unwind, giving rise to macroscopic polarization which saturates at a critical field Ec. The helix dynamics in a.c. fields from 0–20KHz has been observed in the compounds having: 1. positive dielectric anisotropy and low permanent polarization. 2. negative dielectric anisotropy and low permanent polarization. Two relaxation processes have been observed: a “slow” relaxation determined by relaxation time τs = γ (Kqo2)-1 and a “fast” relaxation determined by the relaxation time τf= γ [2α(T*c-T)]-1 (γ is the dynamic viscosity Coefficient). The typical relaxation frequencies for γs and γf correspond to = 400 Hz and = 1 KHz respectively. It has been observed that new textures result from the superposition of dynamics caused by helix and undulation instability created by electric field induced charged layers.