VISCOSITY COEFFICIENTS OF SMECTICS-C

By extending the statistical theory of theological properties of nemat ics, we derive elementary expressions for all phenomenological viscosi ty coefficients of ferroelectric smectics C- in terms of a small numb er of parameters. The results permit estimates of signs and ratios of viscosity coefficients and their tilt angle dependence. It is shown th at 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.