Effects of Electric Fields on the Helical Pitch in Chiral Smectic C Liquid Crystals

Abstract

Electric fields (d.c. or low frequency a.c.) applied perpendicular to the helical axis interact with the Chiral Smectic C (Sm C*) through coupling of the permanent polarization. The helix pitch increases on the application of electric field and unwinds completely at a critical electric field E_c , We report here the experimental observations on the variation of the helix pitch as a function of temperature in the Sm C* phase and frequency of the applied electric field. E_c required to unwind the helix has been measured for a category of Sm C* liquid crystals having:

1.	negative dielectric anisotropy and low permanent polarization,
2.	positive dielectric anisotropy and low permanent polarization,
3.	positive dielectric anisotropy and higher permanent polarization.

The results have been discussed in the light of the method used by de Gennes to calculate E_c for unwinding the helix in cholesterics and extended to the Sm C* phase by Meyer and Martinot-Lagarde, From these measurements it has been possible to calculate permanent electric polarization in these materials.