聚酰亚胺溶液黏度对液晶预倾角的影响

为了制备具有自取向功能的聚酰亚胺(PI)取向膜,避免摩擦工序在取向膜表面造成静电、灰尘、配向不良等不利影响,本实验通过一系列黏度不同且有水平及垂直取向功能的PI溶液,研究了PI液黏度和其取向膜表面粗糙度的关系,进而研究了PI膜表面粗糙度和液晶预倾角(θ_p)的关系。研究发现:取向膜表面粗糙度随着PI液黏度的增大而增大,θ_p随着粗糙度的增大而增大,但当粗糙度大于一定值(3.760nm)后,θ_p增长缓慢并趋于稳定。这主要是因为PI液黏度增大时,阻碍了相邻PI液滴通过分子链段协同运动向彼此扩散的几率,进而形成取向膜表面的"峰谷"形貌,这种"峰谷"形貌表面对液晶垂直取向起到了支撑作用,正是这种支撑作用使得液晶分子获得较大的θ_p。结合液晶面板响应时间对高预倾角的要求和Inkjet PI液滴喷嘴过小对PI液黏度的限制,得出PI液黏度大约为41CP时,此时取向膜表面粗糙度为4.830nm,液晶取向角为5.5°,能较好地满足液晶取向的要求。

Effect of different polyimide solution viscosity on pretilt angle of liquid crystal

To prepare a kind of polyimide (PI) solution with self-alignment function, and avoid producing disadvantage effect (static electricity, particle, alignment error, etc.) on alignment layer with rubbing process, a series of polyimides with different solution viscosity were used to research the relationship between PI solution viscosity and its surface roughness. Meanwhile, the relationship between the surface roughness of PI alignment layer and pretilt angle(θ_p) of liquid crystal was also studied. The results demonstrated that surface roughness of PI alignment layer increased with PI solution viscosity increasing, and also the θ_p increased with the surface roughness increasing, but when the surface roughness exceeded a certain value of 3.760 nm, θ_p began to increase slowly. It was mainly because that the high PI solution viscosity hindered the synergic motion of PI chain segment to diffuse to each other, thus forming the rough surface topography. This kind of "peak-valley" topography played a supporting role to the vertical alignment of liquid crystal and then resulted in the high θ_p. A high θ_p was generated by high PI solution viscosity to reduce response time, but the micron-grade Inkjet head nozzle would be blocked by high PI solution viscosity. We found that when the viscosity of PI solution was 41CP, its surface roughness of alignment layer was 4.830 nm, and the θ_p reached to 5.5°,which can satisfy the two requirements mentioned above well.