Study On Liquid Crystal Optical Alignment Based On Polyimide

With the liquid crystal material was widely used in the field of display,as a common preparation method for liquid crystal alignment layer,the friction method due to its serious shortcomings,has become more and more inapplicability,explore a new liquid crystal orientation technology to replace the friction orientation technology is the need for the development of liquid crystal display technology in future.Optical alignment technology is the most promising technology to replace the friction orientation technology,that as one of the non-contact orientation technology,because of its simple equipment and the ability to control the liquid crystal molecular orientation.This paper uses the 365 nm ultraviolet light exposure,linearly polarized 457 nm laser beam and two orthogonal circularly polarized light interference as the experimental means;Subjects are the glass substrate with orientation layer that was preparation by Polyimide polymers containing azo groups,the empty liquid crystal cell composed by two substrate,and the liquid crystal cell with liquid crystal;use the observed CCD with orthogonal polarizer device to found the sample direct change with different light excitation,Based on the observed experimental phenomena,to analysis summary the liquid crystal orientation characteristics controlled by light.The experiment found that UV irradiation can make the azobenzide play cis-trans isomerism reaction,the azobenzide absorption light energy to become into cis structure,then causes the polymer molecules to rotate,and perpendicular to the surface of the substrate,the liquid crystal molecules will be oriented along the long axis of polymer molecules because of the interaction between liquid crystal molecules and polymer molecules.Using linear polarized 457 nm laser irradiation of the liquid crystal cell,azobenzide absorbed light and break the balance state,play cis-trans isomerism reaction,then become into trans structure and perpendicular to the polarization direction to the direction of rotation,the polymer molecules are arranged along the surface of re orientation in the direction perpendicular to the polarization direction of polarized light,the liquid crystal molecules will change samely like polymer molecules because of the interaction between them.The experimental results showed that the orientation of cell with better than empty cell,the observed image contrast is much larger than that cell without liquid crystal,and the response time is shorter than ten times shorter than the empty cell.Finally,using two orthogonal circularly polarized 457 nm laser to interfere with the surface of the empty cell and the cell filled with liquid crystal,the holographic polarization grating are fabricated successfully.It is found that the diffraction spot of the cell filled with liquid crystal is much brighter than the empty cell that by 632 nm laser probing.The results show that the holographic grating can be fabricated by the empty cell,but the grating prepared by the cell with liquid crystal is better.In addition,when the sample is heated to a certain temperature,the writing of liquid crystal by external light field can be wiped out.The experimental results show that the liquid crystal orientation is not only controlled by the wavelength of the light,but also controlled by the polarization direction of the light.Besides the application value in the display field,the research results of this thesis are also applicable to the development of optical communication liquid crystal devices,such as optical power controller and polarization controller;and it also has a certain reference value for the application of optical orientation technology in the industrialization of the new orientation layer and the optical information storage.