Viscosity coefficients of smectics C∗

Abstract

By extending the statistical theory of rheological properties of nematics, we derive elementary expressions for all phenomenological viscosity coefficients of ferroelectric smectics C∗ in terms of a small number of parameters. The results permit estimates of signs and ratios of viscosity coefficients and their tilt angle dependence. It is shown that a number of coefficients generally appear to be very small and can be neglected in practical calculations. We discuss also the influence of molecular biaxiality on the rotational viscosity of smectics C.