Rotational Viscosity of Smectic C* Phase in Ferroelectric Liquid Crystals

Scient~$c-Research Institute of Organic Intermediate Productsand Dyes, Moscow (Submitted May 20,1987) Zh. Eksp. Teor. Fiz. 94,125-132 (February 1988) The energy dissipation in the smectic C * phase of ferroelectric liquid crystals is analyzed. I t is found that the dynamics of molecular rotation about a normal to the smectic layers and of rotation resulting in a change of the tilt angle of molecules in the layers can be described by introducing two different rotational viscosity coefficients. Methods for experimental determination of the values of these coefficients are developed. Relationships are derived for describing the dependence of the rotational viscosity coefficients of a smectic C liquid crystal on its order parameter; the validity of these relationships is confirmed experimentally. The difference between the rotational viscosity of nematic and smectic C phases of liquid crystals is studied.