Physical properties of some novel nematic bimesogens for the flexoelectriceffect

In a chiral nematic liquid crystal, the flexoelectric effect consists of a fast and linear coupling with an applied electric field. One difficulty to overcome is the unwinding of the helix that occurs at higher fields due to dielectric coupling, The use of bimesogens, which possess very low molecula r dielectric anisotropy can improve flexoelectric characteristics. New bime sogen compounds have recently been synthesised that exhibit switching angle s of 45 degrees for applied fields of about 9 V.mum(-1). In this paper, res ults from dielectric, electro-optic and dynamic light scattering measuremen ts are reported for the new bimesogenic mixture. The dielectric anisotropy Delta epsilon changes sign with temperature and its values range between -0 .2 and 0.3 for the temperature range studied. For Delta epsilon weakly posi tive, no electric field Freedericksz transition could be induced but Willia ms domains are observed instead. The large decrease in the bend elastic con stant to viscosity coefficient ratio is attributed to a large increase in t he bend viscosity coefficient.