Analysis for the dielectric properties of trans-cyclohexyl(tri)biphenyl liquid crystal compounds in microwave frequency bands
At present,the liquid crystal materials used in microwave phase shifters are mostly high birefringence polybiphenyls or polyphenylacetylene liquid crystal compounds as the main components.But these liquid crystal compounds inevitably have some disadvantages such as large viscosity,slightly higher dielectric loss or poor photothermal stability.The trans-cyclohexyl(tri)biphenyl liquid crystal compounds with relatively low viscosity and high thermal stability are widely used in displays devices,but their microwave dielectric properties studies have been fewer reported.In this paper,six compounds of trans-cyclohexylbiphenyl and tri-biphenyl isothiocyanate were synthesised selectively,and their liquid crystal phase and microwave(10～30 GHz)dielectric properties were tested.Their dipole moments and polarizabilities were calculated by molecular simulation using density functional theory(DFT),and compared with the properties of the related polybiphenyl liquid crystal compounds to explore the effect of the trans-cyclohexyl structure on the microwave dielectric properties of liquid crystal molecules.The experimental results show that the isothiocyanato-trans-cyclohexyl(tri)biphenyl liquid crystal compounds not only have relatively low melting points(<90℃)and wide nematic temperature ranges(86～160℃),but also have low maximum dielectric losses(≤7.25×10-3)at 10～30 GHz,which makes their microwave quality factors relatively high(η≥30)and suitable to be used as effective components in microwave-usable liquid crystal materials.
trans-cyclohexyl(tri)biphenylliquid crystals for microwaveslow dielectric losswide temperature nematic phasesynthesis
万方数据
维普
