含氟三环NCS液晶材料的介电性能研究

Dielectric properties of fluorine-containing tricyclic NCS liquid crystal materials

为了探究液晶材料的介电性能,本文研究了4PPTGS和4PUTGS两种含氟三环NCS类液晶材料的介电各向异性和介电损耗。首先用精密LCR表(Agilent E4980A)测量液晶盒的电容并用双盒模型和液晶盒电容模型得到4PPTGS和4PUTGS两种液晶材料的平行和垂直介电常数,再由电压-电容特性曲线得到它们的阈值电压,并进一步探讨了介电各向异性和阈值电压对温度的依耐性;然后,在20 Hz^10kHz范围内研究了外加电压频率对液晶材料介电损耗的影响,两种液晶材料在1kHz左右都存在介电损耗峰值,为了减小器件的功耗和提升器件的质量,液晶材料应选择在介电损耗小的频率下工作;最后,通过对平行和垂直排列向列相盒中液晶材料在不同电压下介电损耗的测试与分析,介电损耗的变化是由于在外加电场下液晶分子固有偶极矩的取向极化引起的,介电损耗值的大小与液晶分子的排列状态密切相关。此项研究对提升液晶材料在应用中的介电性能具有一定的指导意义。

In order to investigate the dielectric properties of liquid crystal（LC）materials,the dielectric anisotropy and dielectric loss of two fluorine-containing tricyclic NCS LC materials,4 PPTGS and 4 PUTGS,were studied in this paper.Firstly,the capacitances of the LC cells were measured with a precision LCR meter（Agilent E4980 A）.The parallel and vertical dielectric constants of both LC materials were obtained by using the dual-cell model and the LC cell capacitance model.On the basis of the voltage-capacitance characteristic curve,we further explored the dependence of dielectric anisotropy and threshold voltage on temperature.In addition,the effect of applied voltage frequency on the dielectric loss of LC materials in the range of 20 Hz～10 kHz were studied.There are dielectric loss peaks around 1 kHz for both LC materials.Consequently,to reduce the power consumption and improve the quality of the device,LC materials should be selected to work at the frequencies with low dielectric loss.Finally,the dielectric loss of LC materials in parallel and vertical aligned nematic cells were tested and analyzed for different voltages.The change of the dielectric loss is due to the orientation polarization of the intrinsic dipole moment of the LC molecules under the applied electric field,and the value of dielectric loss is closely related to the arrangement of the LC molecules.This paper has a certain guiding significance for improving the dielectric properties of LC materials in applications.