Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, Vol.366, 2567-2576, 2001
Physical properties of some novel nematic bimesogens for the flexoelectric effect
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 molecular dielectric anisotropy can improve flexoelectric characteristics. New bimesogen compounds have recently been synthesised that exhibit switching angles of 45 degrees for applied fields of about 9 V.mum(-1). In this paper, results from dielectric, electro-optic and dynamic light scattering measurements 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 positive, no electric field Freedericksz transition could be induced but Williams domains are observed instead. The large decrease in the bend elastic constant to viscosity coefficient ratio is attributed to a large increase in the bend viscosity coefficient.
Keywords:bimesogens;dielectric anisotropy;Williams domains;dynamic light scattering;visco-elastic properties