Reorientation of the director and the bonds in a hexatic smectic phase

Some smectic liquid crystal phases exhibit a long range bond-orientational order. In hexatic smectic phases with molecules tilted towards the layers director rotations are combined with distortions of the bond net. The coupling of the director to the bond field influences strongly the threshold behaviour of the Freedericksz transition of planar oriented smectic I films sandwiched between parallel plates. In contrast to nematic and smectic C films, the threshold voltage depends on the film thickness. Investigating this thickness dependence several material parameters can be obtained by adjusting the experimental data to the threshold formula.