Unwinding of the Helical Texture of a Smectic C* Liquid Crystal, Through Ferroelectric and Dielectric Anisotropic Coupling With an Applied Fiel

A large enough DC or low frequency AC field couples to the permanent polarization P and unwinds the helical texture of a smectic C* liquid crystal.′ From the measurement of the unwinding critical field, one can deduce the value of P. We present here a general model to compute the unwinding critical field; this model takes into account both the effects of P, and of the dielectric anisotropy. This point will be useful to an understanding of the AC high frequency regime.2