光控取向弱锚定表面的液晶分子排列

Liquid Crystal Molecules Alignment on the Weak Anchoring Surface by LPP Method

研究了光敏聚酰亚胺ＰＩ（ＢＴＤＡ－ＴＭＭＤＡ）用于液晶取向时的弱锚定边界特性。实验测得了两基板皆为摩擦取向层扭曲向列液晶显示器件（ＤＲ－ＴＮ－ＬＣＤ）及两基板皆为光控取向层的扭曲向列液晶显示器件（ＤＬＰＰ－ＴＮ－ＬＣＤ）的电光特性和时间响应特性曲线。研究了液晶排列的稳定性，讨论了液晶分子在光控取向弱锚定表面上的排列机理。

A new method is studied, which can align the liquid crystals by the linear polarized photo-polymerization (LPP) using ultraviolet (UV) light. The weak anchoring properties of the photosensitive polyimide PI(BTDA-TMMDA) are investigated, by which the liquid crystal molecules are aligned. The experiment results shows that the liquid crystals are uniformly aligned by the polyimide PI(BTDA-TMMDA) only through the exposure of the polarized UV light for 30 minutes. The electro-optical and response time characteristic curves of TN-LCDs made of the double-rubbed (DR) and double-linear polarized pho- topolymerization (DLPP) substrates are measured. It shows that the threshold voltage (Vth = 1.22V) and the saturated voltage (Vsat=1.69V)of DLPP-TN-LCD are lower than the DR-TN-LCD's (Vth=1. 92V,Vsat=2. 65V) due to the weak anchoring on the surface. The response time TON (14ms) of the DLPP-TN-LCD is shorter than the DR-TNLCD'S (TON= 27. 5ms), and TOFF(82. 5ms) is longer than DR\TN-LCD's (TOFF= 43. 5ms). The LC is aligned uniformly after treated 30min at 130℃. The mechanism of LC alignment on the weak anchoring surface is also discussed. IR spectral difference of polyimide surface before and after exposure of polarized UV light shows that the spread of the carboxyl (C= O) is different between the directions perpendicular and prarllel to the vector of the polarized UV light, so the anisotropy is produced on the PI surface. Thus, the liquid crystal molecules are aligned under the influence of the anisotropic PI surface.