Thin-cell dielectric response of a ferroelectric liquid crystal

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Abstract
The results of a study of the dielectric response of the liquid crystal BOH8-MPOOBC in the frequency range 5 Hz to 13 MHz, in the vicinity of the phase transition to the ferroelectric phase, in an aligned cell of 2.7 μm thickness, are presented. At small ac probe fields, critical-like behavior is observed in the dielectric permittivity and the characteristic relaxation time of molecules in the bulk of the sample. At high ac probe fields, a second relaxation appears due to the reorientation of molecules at the cell surfaces. The dielectric strength of the bulk relaxation grows linearly with the spontaneous polarization. The viscosities of the surface and bulk processes, as determined from measured characteristic times and spontaneous polarization, increase in a thermally activated manner for temperatures within the ferroelectric phase. Comparison of frequency-dependent optical response and dielectric response measurements at small applied fields shows that both are due to the same bulk molecular reorientation process.