Effect of electric field on layer compression modulus of smectic A liquid crystals

An apparatus for measuring the mechanical properties of liquid crystals over the frequency range from 100 MHz to 1 kHz was constructed. It was used to study the effect of a static and longitudinal viscosity of a smectic-A liquid crystal having homeotropic alignment. The static electric field was applied perpendicularly to the smectic layers. The specimen used was octylcyanobiphenyl (8CB). The layer compression modulus was found to increase by 0.5% at 7.6 kV/cm, and the amount of increase is proportional to the square of the applied field. This change in the layer compression modulus is reversible with respect to the on-off characteristics of the electric field. This phenomenon is explained by the theory of G. Grinstein and R.A. Pelcovits (see Phys. Rev., vol.A26, p.916, 1982)