液晶分子与高分子取向膜相互作用强度的定量研究

In the work, the twisting movement ruled by desorption-adsorption model was designed, and the effective adsorption energy of a liquid crystal molecule on polymer film surfaces was obtained as 1eV. The result was proved to be reasonable by the experiment.The total work dealt with the twist angle distribution in the interface layer of liquid crystals, the orientational order parameter and the thickness of this interface layer. The wedge cell was adopted and the relation between anisotropic infrared absorbance and the liquid crystal thickness was measured. The orientational order parameter distribution was also obtained. From this result, it is clear that the surface order parameter is always smaller than that in bulk although the surface rubbing treatment is very strong. The surface order parameter goes up to a saturation value of 0.26 when the rubbing strength is increased, but the order parameter in the bulk keeps in constant as 0.6 no matter how the rubbing treatment is made. The interface layer thickness of liquid crystals is about 7nm. These results suggest that rubbing treatment is not able to control the orientation of every liquid crystal molecule, and it can only give a essential order and a orientation axis. In fact, liquid crystals have the capability to align themselves in a common orientation so that those molecules in the interface layer improve their orientational order only by 7nm of thickness. In the experiment, the anchoring strength of alignment caused by surface molecular adsorption was also investigated. However the maximum anchoring strength caused by adsorption was only 30μm-1, 1/10 of the rubbing effect. Therefore, the alignment formed by molecular orientational adsorption is hard into practice. It also implies that anchoring strength is no matter with adsorption energy.Through above work, we realized that the alignment films should have molecular orientation in itself. And then, we challenged a new alignment method, photo-alignment. Photo-alignment is a kind of method without touch with each other, in which there will be no electric charges or dusts brought into liquid crystal cells. The method of photo-alignment was proposed in the beginning of 1990's, but it has not come into practice, yet. We designed the molecule with photo-sensitive parts in both ends of the molecule and made the photo-polymerization in a common direction. A good alignment result was obtained..The above are the frontier results in the world. They give important contribution to understanding mechanism of liquid crystal alignment, and guidance to designing or renovating the alignment method.

为探索液晶分子与高分子取向膜之间的相互作用机理，本研究将利用热力学控制的动力学过程，探讨界面处液晶分子的脱附几率，进而求得吸附能。由于所利用的动力学方程中涉及液晶扭曲角度的分布，从而使得与扭曲弹性常数相关的分子排列有序度的分布成为重要实验内容。本研究将给出界面处的定量参数，为构思界面匹配性能更好的液晶器件提供理论依据。