Surface dynamics of a freely standing smectic-A film

A theoretical analysis of surface fluctuations of a freely standing thermotropic smectic-A liquid-crystal film is provided, including the effects of viscous hydrodynamics. We find two surface dynamic modes (undulation and peristaltic). For long wavelengths and small frequencies in a thin film, the undulation mode is the dominant mode. Permeation enters the theory only through the boundary conditions. The resulting power spectrum is compared with existing: experiments. It is also shown that feasible light scattering experiments on a freely standing smectic-A film can reveal viscosity and elastic coefficients through the structure of the power spectrum containing contributions from both the undulation and peristaltic modes.