The ferroelectric polarization of liquid crystals and its measurements

In liquid crystals, the chiral tilted smectic phases only present, a spontaneous (ferroelectric) polarisation, which is due to the molecular rotations cramped by the structure in these phases. The amplitude of the polarisation given by a polar group on the molecule varies with the distance of this group from the chiral part. This spontaneous polarization is a very important parameter because its linear coupling with an applied electrical field is the basis of all applications of these compounds. The measurement of the polarization is obtained from the current induced when it is reversed. I comment on different methods to obtain a good measurement by polarization reversal in the whole sample and separation of the reversal current from the ionic and displacement currents.