Control of Liquid Crystal Alignment Based on 3-Dimensional Molecular Manipulation

液晶的均匀排列对于它们的光学和光电应用是必不可少的，这通常是通过机械摩擦聚酰亚胺(PI)层来获得的。然而，摩擦过程中会产生粉尘颗粒和表面静电，这会对薄膜晶体管造成电气和机械损伤。近年来，线偏振紫外光照射下聚酰亚胺薄膜引起的液晶单向取向技术得到了发展。该方法允许容易地控制对准方向和快速制备对准层，并且造成很少的灰尘颗粒和静电损害。在这种情况下，液晶的对准垂直于LPUV光的偏振，为了给出准确的LCS预倾斜，应进行两次曝光。在这个项目中，我们开发了一种新的方法，通过在热处理过程中照射来诱导液晶与LPUV光的偏振平行对准。在热亚胺化过程中，用8.5 mW/cm2的低功率紫外光照射涂覆聚酰胺酸的ITO玻璃基板。辐照时间约为30min，热处理温度为10 0~2 5 0℃，升温速率为5℃/mm。辐照后，底物在250℃下亚胺化10min。用上述两片平行极化轴的衬底构建了间距为5μm的液晶盒。4‘-戊基-4-氰基联苯(5CB)掺杂0.3wt%二向色性染料M-137(λmax=639 nm)，在75℃下以各向同性相填充到电池中，冷却至室温。通过偏光显微镜和偏光紫外可见光谱分析发现，所制备的液晶分子呈均匀排列。

Uniform alignment of liquid crystals (LCs) is indispensable for their optical and optpelectronic applications, which is conventionally obtained by mechanically rubbing a polyimide (PI) layer. However, dust particles and static surface charges are produced by the rubbing process, which would cause electrical and mechanical damage to thin film transistors. In recent years, the technique for unidirectional alignment of LCs caused by PI films exposed to linearly polarized UV (LPUV) light has been developed. this method allows for easy control of the alignment direction and the fast preparation of an alignment layer, and causes little dust particles and electrostatic damage. In this case, the alignment of LC is perpendicular to the polarization of LPUV light, and exposure should be made two times in order to give precise pretilt of LCs. In this project , we developed a novel method to induce a parallel alignment of LC to polarization of LPUV light by irradiating during the thermal treatment process. Polyamic-acid-coated ITO glass substrate was irradiated with LPUV light at 8.5 mW/cm^2 during the thermal imidization process. The irradiation time was about 30 min and the thermal treatment was processed from 100 to 250 ℃ at a heating rate of 5 ℃/mm. After irradiation, the substrate was then imidized for 10 min at 250 ℃. LC cells with a gap of 5 μm were constructed using two pieces of the above substrates with parallel polarization axes. 4'-Pentyl-4-cyanobiphenyl (5CB) doped with 0.3 wt% dichroic dye M-137 (λmax = 639 nm) was filled into the cells in an isotropic phase at 75 ℃ and cooled down to room temperature. By polarizing microscopy and polarized UV spectra, it was found that the LC molecules were aligned uniaxially and uniformly.