Syntheses and characteristics of polyimides for the applications to alignment film for liquid crystal display

Abstract

ABSTRACT:In this work, several polyimides (PIs) containing diphenyl ether group were synthesized and characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis. The relationship between the surface structures and the molecular chain conformations of the PIs, whether helical or zigzag, was discussed. The effects of the molecular chain conformations of the PIs on the pretilt angles of liquid crystal molecules were systematically investigated. The surface orientations of polyimides whose chains adopt zigzag and planar conformations were less improved by rubbing treatment than those of polyimides whose chains adopt helical and nonplanar conformations, because the polyimide chains of zigzag and planar conformation are easily packed. The polyimides, whose chains adopt helical and nonpolar conformations, gave larger pretilt angles than the polyimides whose chains adopt zigzag and planar conformations. The pretilt angles measured under the condition of rubbing depth of 0.5 mm were smaller than under the condition of rubbing depth of 0.3 mm.

A study of the stabilization of vertical alignment for liquid crystals by increasing the side‐chain rigidity of polyimides

“…Because it is widely believed that the generation of pretilt angle is highly dependent upon the interaction of PI with LC, great attention has been paid to the effect of functional diamine content on pretilt angle of LC cells. As reported above, for PI1, PI2 and PI3, the lowest content of functional diamine in total diamines to ensure vertical alignment performance is 10, 15 and 25 mol%, respectively.…”

Influence of Chain Stiffness and Preparation Methods on the Efficiency of Polyimide Alignment Layers for Liquid Crystal Orientation

“…In this measurement setup, the test cell is rotated in a linearly polarized laser beam, and the intensity of the light transmitted by the analyzer is recorded as a function of the angle of light incidence. The pretilt angle values range between 0.7 and 5.1 (Table 5), which are typical for polyimide alignment layers [14]. For LC cells with rigid PAE 1, the pretilt angle was increased from 2 for the buffed precursor alignment layer (A) to 3 after imidization (B).…”

“…PI alignment layers are typically prepared from precursor solutions of poly(amic acid)s or PAEs, which are thermally imidized to polyimide layers and finally surface oriented by buffing [13,14,20]. To systematically study the effect of several experimental and structural parameters on the performance of alignment layers, these layers were incorporated in standardized LC guest-host cells, and the DR served as layer performance indicator.…”

“…The pretilt angle is directly influenced by the inclination angle of the polymer backbone structure, which is oriented along the buffing direction and inclined up from the film surface [10][11][12]. Thus the pretilt angle is determined by LC anchoring, a complex interplay of steric repulsions and electronic interactions [13,14]. For buffed aromatic PI alignment layers, the pretilt angle is typically below 5 [14].…”

“…Thus the pretilt angle is determined by LC anchoring, a complex interplay of steric repulsions and electronic interactions [13,14]. For buffed aromatic PI alignment layers, the pretilt angle is typically below 5 [14].…”