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-ODNCnMPD 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.

Renewable, Eugenol—Modified Polystyrene Layer for Liquid Crystal Orientation

“…The conventional method of mechanical rubbing of polyimide (PI) surfaces commonly used in the display industry produces stable LC orientation layers on these surfaces [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ]. Polyimide derivatives containing hydrophobic long alkyloxy and/or alkyl side chains such as ( n -decyloxy)biphenyloxy and n -octadecyl groups have been improved for use as vertical LC orientation layers [ 26 , 27 , 28 , 29 ]. However, PI derivatives require a high baking temperature of over 200 °C for their synthesis from the PI precursor to apply the LC orientation layers on plastic substrates for versatile displays.…”

Liquid crystal alignment behaviours on poly(methyl methacrylate) having polyhedral oligomeric silsesquioxane groups

“…[2,3] Polyimide derivatives having longchain alkyl or alkyloxy groups have been synthesised in order to use them as vertical LC alignment layers. [4][5][6][7] Hard baking processes are used to produce polyimide alignment layers and the hard baking temperature of the polyimide films is usually over 200°C, which is too high for manufacturing flexible plastic devices. Therefore, lower temperature processes using comb-like polymers, irradiating photoreactive polymers with UV light and fabricating micro-and nanostructures have been investigated to achieve the vertical LC alignment.…”

Alignment Layer of Liquid Crystal Using Plant-Based Isoeugenol-Substituted Polystyrene

“…Polyimide (PI) derivatives are most commonly used as LC aligning materials using the rubbing technique because they provide stable LC-aligning properties [ 66 ]. Polyimide derivatives having alkyl and/or alkyloxy side groups, such as polyimide derivatives containing octadecyl and n -decyloxybiphenyloxy side chains, exhibit vertical LC aligning behaviors [ 67 , 68 , 69 ]. Although polyimide derivatives have been widely employed in the display industry, polyimide precursors are treated at high temperatures in order to produce polyimide film, and the film itself shows a yellowish color.…”