Preparation of vertical alignment layers by blending polyimide precursors with and without side chains

Abstract

2009) Preparation of vertical alignment layers by blending polyimide precursors with and without side chains, Liquid Crystals, 36:2, 173-178, A series of polyimides (PIs) were prepared from the precursors, blends of a poly(amic acid) and a side-chain poly(amic acid), based on a diamine 4¢-(tert-butyldimethylsiloxy)biphenyl-4-yl 3,5-diaminobenzoate (DPA). The blended polyimide (bl-PI) films were relatively tough. The surface properties of the bl-PI films were characterised by surface energy measurement, X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance infrared spectroscopy (ATR-IR). The results showed that the non-polar side chains were highly enriched on the surface and 90 pretilt angles of liquid crystal molecules were generated regardless of side chain content. For comparison, the copolyimides (co-PI) with different DPA contents were synthesised. It was found that the enrichment of the side chain on the surface increased with increasing DPA content and the pretilt angles of liquid crystal molecules rose from 3 to above 20 when DPA content increased from 10% to 30%. For the polyimides based on a diamine without a non-polar end group, 4¢-biphenyl-4-yl 3,5-diaminobenzoate (DABBE), both bl-PIs and co-PIs could only generate the same low pretilt angles. In conclusion, by blending poly(amic acids) based on DPA, tough vertical alignment layers could be prepared.

Multiple Alignment Modes for Nematic Liquid Crystals Doped with Alkylthiol-Capped Gold Nanoparticles

“…Because of their high thermal stability and mechanical strength, polyimides are most commonly used as rubbed polymer alignment materials, and significant research efforts have been geared toward modulating the chemical structure of polyimides. Chemical modification and mixing of different polyimides now allow for improved planar alignment (i.e., the long molecular axis of rod-like nematic LCs aligns parallel to the surface) − , homeotropic (vertical) alignment of rod-like LCs, commonly without rubbing (i.e., the short molecular axis aligns parallel to the surface) − , or enable tuning of the LC alignment between planar and vertical. (i.e., tuning the pretilt angle of the LC molecules) − .…”

Mesogen-co-polymerized transparent polyimide as a liquid-crystal alignment layer with enhanced anchoring energy

“…[4][5][6][7] However, the pretilt angle and non-uniform alignment of LCs in large-sized substrates may limit the performance of display panels. [8][9][10][11] The ability to align LC molecules on an alignment layer surface is affected by the surface topography and intermolecular interaction between LC molecules and matrix polymer chains. In general, this ability can be characterized by two performance parameters, namely the pretilt angle of the LC molecules and the surface azimuthal anchoring energy.…”

“… 4–7 However, the pretilt angle and non-uniform alignment of LCs in large-sized substrates may limit the performance of display panels. 8–11 …”