Alignment layers based on poly(oxadiazole‐naphthylimide)s: New aspects on tuning anisotropy of the surface morphology and adhesion via rubbing

Abstract

Two poly(oxadiazole-naphthylimide) films are prepared and characterized to elucidate their suitability as alignment layers for nematics in display devices. First, rheological behavior is analyzed to establish in correlation with molecular modeling the optimal conditions of solution shearing to obtain uniform films by spin coating. Second, the polymer foils are subjected to rubbing with cellulose diacetate cloth to induce surface anisotropy required for nematic orientation. Novel insights are extracted here by studying the effect induced by the positioning of the textile fiber parallel/orthogonal to the rubbing direction on the induced polymer morphology through atomic force microscopy. The balance between the isotropic and anisotropic characters of the surface morphology of the unrubbed and rubbed polyimide (PI) samples is evaluated by Fourier spectrum integrated into polar coordinates and autocorrelation function analysis. The involvement of the created surface features on the anisotropy of the interfacial PI/nematic adhesion is further investigated. The qualitative orientation ability of the surface textured samples is evaluated revealing that both PI chain flexibility and fiber positioning are paramount for attaining uniform orientation of the nematic.

Prominent processing techniques to manipulate semiconducting polymer microstructures

“…345 While mechanical rubbing is cost-effective (the equipment is cheap and easy to fabricate) and efficient (highly oriented polymer films can be obtained by repeating the rubbing procedure even tens of times 346 ), this technique carries along some disadvantages: it efficiently orients polymer chains located only at the near-surface region of the films and might produce electrostatic charges and dust particles. 345,347 Although the technique of mechanical rubbing is mostly known for its use in the alignment of PI substrates employed in flat panel liquid crystals displays, 347 nowadays it has been broadly utilized to uniaxially orient polymer films, 348 including conjugated poly(2,5-dinonyloxy-1,4-phenylenevinylene), 349 P3HT, [350][351][352] PBTTT, 353,354 etc. In most of these latter cases, rubbing was conducted to boost the (out-of-plane) anisotropic OFET charge mobility.…”