Sojeong Lee

Liquid-crystal alignment on the rubbed film surface of semi-flexible copolyimides containing n-alkyl side groups

Abstract Semi-flexible copolyimides with various alkyl chain lengths (BTDA-ODA/CnMPD PIs) were newly synthesized in N-methyl-2-pyrrolidone from benzophenonetetracarboxylic dianhydride, 4,4′-oxydiphenylene diamine, and 3,5-diaminobenzoyl n-alkanoates. The films were rubbed with varying rubbing densities, and on the rubbed surface the alignment behavior of a nematic liquid-crystal (LC) was examined. LCs were always aligned along the rubbing direction either homogeneously or homeotropically, depending on the side chain length as well as the rubbing density. The results inform that flexible n-alkyl side groups in the copolyimide play a critical role to align LCs on the surface, and their role is strongly dependent on its length. In addition, thermal, optical, and dielectric properties were investigated.

Novel polypyromellitimides and their liquid crystal aligning properties

Various aromatic poly{3,6-bis[(4-n-alkyloxy)phenyloxy]-pyromellitimide}s {poly(Ar-C m -PMDA)s, m = 1, 4, 8, 12] were prepared in film form by routine two-step condensation of 3,6-bis[(4-n-alkyloxy)phenyloxy]pyromellitic dianhydrides (C m -PMDAs) with various aromatic diamines. After characterization of their chemical structures their solution, thermal and liquid crystal (LC)-aligning properties in terms of pretilt angle at various rubbing densities were measured and discussed with respect to their backbone structures. All polyimide films showed excellent thermal stability and homogeneous LC alignment, but the poly(p-phenylene-C 12 -PMDA) exhibited completely homeotropic alignment while the pretilt angle values of poly(p-phenylene-C 8 .-PMDA) varied with varying rubbing density.

Fully rodlike polyimides containing flexible side chains with various lengths and their ability to align liquid-crystals on the rubbed surface

Abstract Rodlike poly(p-phenylene pyromellitimide)s with various side chains (Cm-PMDA-PDA Pis) were newly prepared in a good quality of films. The polyimide films were rubbed, and used in constructing liquid-crystal (LC) cells which were filled with a nematic LC containing a dichroic dye. For the LC cell, both pretilt angle and alignment director of LCs were dependent strongly on the side chain length as well as the rubbing density. On the polymer film, both homogeneous and homeotropic LC alignments were achievable by either changing the side chain length or varying rubbing density. Unlike polymers reported previously as a LC alignment layer material, the Cm-PMDA-PDA PI induced LCs to pretilt with a negative angle rather than a positive angle: this is a unique property characteristic of the Cm-PMDA-PDA PIs. In addition, film properties were measured.

Alignment behavior of liquid-crystal molecules on the surface of photoreactive polymer films treated by Uv-irradiation and rubbing

Abstract Photoreactive polyimides, which contain cinnamoyl and 4-fluorocinnamoyl moieties as side groups, were synthesized, providing a good quality of films. For these polymers in thin films, the photoreactivity and photoreaction-induced polymer alignment were examined by polarized and unpolarized uv-exposures and uv-visible spectroscopy. And, their rubbing processability was investigated. The alignment and pretilt of LCs on the film were dependent upon all the process parameters (polarization, exposure dose, and exposing method of uv light and rubbing density) as well as the fluoro substituent.

New Photoreactive Polymers Containing Short Side Chains as Orientation Layer Materials: Effect of Side Chain Lengths on the Alignment of Liquid-Crystals

Abstract A series of photoreactive polymers having cinnamoyl moieties with various flexible chain lengths as side groups were newly synthesized. The polymers were soluble in common organic solvents, producing a good quality of thin films in spin- and bar-coating and subsequent baking process. Their photoreactivity to UV light and photoalignment behavior were determined. And the polymers were evaluated as an orientation layer material to control the alignment of liquid-crystals on the film surface.

A Rodlike Polymer with Various Side Chain Lengths and its Ability to Align Liquid-Crystals

Abstract A rodlike polymer with various side chain lengths was prepared in a good quality of films. The polymer films were rubbed, and used in constructing liquid-crystal (LC) cells which were filled with a nematic LC containing a dichroic dye. For the LC cells, the ability of polymers to align LCs was evaluated, and compared to that of semi-rigid polymer containing the same type of side chains as the rodlike polymer had.

A new class of photoreactive polymers for liquid-crystal displays: Synthesis and properties

Abstract High performance photoreactive polyimides with various side chains were newly synthesized. These polymes contained phenylvinylpyridine moieties as phtoreactive side chains. The polymers were soluble in common organic solvents, giving a good quality of thin films. For the polymers, photoreactivity and photoaligning ability were investigated. Further, the polymers in films were evaluated as an orientation layer material to control the alignment of liquid-crystals on the surface.