外加电压频率对液晶介电各向异性的影响

液晶材料的介电各向异性通常与频率有关。为进一步研究频率对液晶材料介电常数的影响,首先,使用紫外可见分光光度计(METASH UV-9000S)和表面轮廓仪(Contor GK-T)分别测量液晶盒厚度以及聚酰亚胺(PI)取向层厚度,通过精密热台(LTS 350)控制实验温度20℃,使用精密LCR表(Agilent E4980A)测定4种不同液晶材料在100～2 000Hz的频率内的平行和垂直排列向列相液晶盒电容;然后,利用液晶盒电容模型计算出不同频率下液晶的平行和垂直介电常数,并绘制频率-介电各向异性曲线;最后,分析频率对液晶介各向异性的影响。实验结果表明:温度一定,正性液晶的介电各向异性随频率的升高而减小,然后逐渐趋于平缓,负性液晶的介电各向异性随频率变化基本保持不变。此项研究对进一步分析液晶材料的介电特性具有一定的指导意义。

Influence of the frequency of external applied voltage on the dielectric anisotropy of liquid crystal

The dielectric anisotropy of liquid crystal materials is usually related to the frequency. For further investigations of the influence of frequency on the dielectric constant of liquid crystal materials, firstly, the thickness of the liquid crystal cells and the thickness of the polymide (PI) orientation layers were measured by UV spectrophotometer (METASH UV-9000S) and Surface Profiler (Contor GK-T) respectively. The precision hot-stage (LTS 350) was used to control the experimental temperature of 20℃, and the capacitance of parallel and vertical aligned nematic liquid crystal cells were measured by a precision LCR meter (Agilent E4980A) at the frequency of 100~2 000 Hz for four different liquid crystal materials. Then, the parallel and vertical dielectric constants of liquid crystals at different frequencies were calculated through the capacitance model of LC cell, the curves of dielectric constant versus frequency were plotted as well. Finally, the influence of the frequency of external applied voltage on the dielectric anisotropy of liquid crystal was analyzed. The experimental results showed that the dielectric anisotropy of the positive liquid crystal decreased with the increase of the frequency at a certain temperature first, and then gradually flatten out, while dielectric anisotropy of negative liquid crystal remained unchanged with the change of frequency. This research has a guiding significance for further analysis of the dielectric characteristics of liquid crystal materials.