COLLECTIVE DIRECTOR MODES AT THE TRANSITIONS TO HEXATIC FERROELECTRICLIQUID-CRYSTALLINE PHASES

Measurements of the dielectric constant and the modulation depth of th e light intensity as a function of temperature and electric field freq uency are reported for two compounds of the homologous series ylbutano yloxy]-4'-[4-n-alkyloxybenzoyloxy]biphenyl exhibiting cholesteric, sme ctic-A, smectic-C*, hexatic-I*, and hexatic-F* phases. Relaxation pro cesses related to the hexatic-I-smectic-C* and hexatic-to-hexatic pha se transitions are characterized and the results discussed in terms of bond orientational order and its coupling to the molecular tilt direc tion. Parameters describing this coupling are determined by fitting th e results of a theoretical model to the experimental data.