THE THICKNESS MODE CONTRIBUTION TO THE PERMITTIVITY OF FERROELECTRIC LIQUID-CRYSTALS

Dielectric properties of a material prepared of valine in the ferroele ctric SmC phase are studied in the frequency range 100 Hz divided by 1 MHz and for the sample thickness d between 6 and 100 mu m for both h elicoidal and twisted sample structure. In all studied samples a low f requency relaxation has been found with the relaxation frequency propo rtional to 1/d(2) and with the contribution to permittivity proportion al to d(2). we suggest this relaxation to be assigned to a 'thickness mode', which is a fluctuation of the molecular twist existing within t he smectic layers in the direction of the sample plane normal. This tw ist deformation existing in both helicoidal and twisted samples is fix ed by the anchoring on the sample surfaces. It is shown that the thick ness mode is an important source of permittivity in the SmC phase of the studied material.