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

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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 Ec , 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. Ec required to unwind the helix has been measured for a category of Sm C* liquid crystals having: The results have been discussed in the light of the method used by de Gennes to calculate Ec 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.