Complex dielectric constant of an antiferroelectric liquid crystal family represented by 4-(1-methylheptyloxycarbonyl) 3-fluorophenyl 4'-dodecylbiphenyl-4-carboxylate was measured in the frequency range between 10-2 Hz and 107 Hz. The experimental results were analyzed using a generalized Cole-Cole expression, and seven dielectric relaxation modes were confirmed to exist. Possible models of collective molecular motions are proposed for mode assignments on the basis of the experimental results of temperature dependence of the modes, together with those of cell gap and bias field dependences.

The phase sequence of a new family of chiral smectic liquid crystals, represented by 4-(1-methylhepthyloxycarbonyl) 3-fluorophenyl 4′-dodecylbiphenyl-4-carboxylate (MHFPDBC), were investigated by measurements of dielectric dispersion under various bias field strengths. Three phases, ferrielectric smectic Cγ * phase (SmCγ *), antiferroelectric phase (AF) and ferrielectric phase (FI), were confirmed between ferroelectric SmC* phase and antiferroelectric SmC A * phase. In the dielectric measurements around the ferrielectric phases, an opposite bias treatment prior to the application of the target bias field strength is important. Observed dielectric relaxation modes were discussed together with the results of electrooptical and conoscopic observations.

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