Application Of High Dielectric Alignment Layer In Liquid Crystal Display

Nowadays,Liquid crystal displays（LCDs）are widely used in our daily lives,such as mobile phones,televisions,computers,automotive instrumentations,displays of home appliances,and so on.In order to meet the needs of people,new models,new materials,and new technologies are proposed to achieve faster response,higher contrast,and wider viewing angles.The material with high dielectric constant can significantly affect the distribution of the electric field,so this kind of material has great potential in liquid crystal display.In this thesis,polyvinylidene fluoride（PVDF）as alignment layer in liquid crystal displays were analyzed.The optical property,mechanical property,thermal stability and electrical property of PVDF was measured.Experiments show that the absorbance of PVDF material is 0.2（or less）in visible light,which is better than the conventional alignment material polyimide（PI）,and the average transmittance of ITO glass substrate coated with PVDF in visible light range is higher than that of ITO glass substrate coated with PI.The alignment effect can be generated by mechanical friction and the liquid crystal molecules are ordered or aligned,and PVDF can maintain good thermal stability as temperature is lower than 400°C.Since the dielectric constant of PVDF is usually between 6.0 and 8.0,it has significant effect on the distribution of the electric field in the liquid crystal display,and its dielectric loss is also less than PI.Twist-Nematic Liquid Crystal Displays（TN-LCDs）were made.The electro-optical curves and switching behavior of TN-LCDs were tested.The lower operating voltage and the faster response time was obtained from experiment.It can be confirmed by experiments that PVDF could be used in LCD as the alignment layer.In order to understand the interaction between PVDF alignment layer and liquid crystal molecule,the pretilt angle of liquid crystal molecules on the surface of PVDF alignment layer was measured by crystal rotation method.Result shows that the pretilt angle is 4.1°.The polar anchoring energy of the substrates with PVDF alignment layer were researched by fully-leaky guided mode technique.Theoretical results and the experimental results about the polarisation-conserving signals of reflectivity(R_SS)recorded by full-leaky guided mode in liquid crystal technique are analysed to evaluate the anchoring energy of PVDF alignment layer.The result shows that the polar anchoring energy between PVDF alignment layer and liquid crystal molecules is 2.8×10^-4 J/m²Results show that PVDF can be used as the alignment layer of LCD for better performance.The research is of guiding significance to study the application of high dielectric materials in LCDs.