The pumping phenomenon in smectic C* liquid crystals

It is known from experiments that smectic C* liquid crystals arranged in a bookshelf geometry between two parallel glass plates can exhibit a pumping phenomenon under the application of an electric field when the lower plate is fixed and the upper plate is allowed the possibility of some movement. This phenomenon, which reflects a change in the cell thickness via mechanical vibrations of the top plate, is known to occur when the direction of an applied electric field is suddenly reversed. An elementary model is developed that describes some of the key features of this effect and is directly relevant to the observations reported in the literature. Two aspects are considered: first, the effect of a simple field reversal, and secondly, the frequency-induced effects of an alternating electric field. A steady increase in the cell thickness occurs under alternating fields and this reflects a pumping phenomenon as the director orientation couples to the flow.