Unusual Alignment of Liquid Crystals on Rubbed Films of Polyimides with Fluorenyl Side Groups

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• 作者：Suk Gyu Hahm ; Taek Joon Lee ; Taihyun Chang ; Jin Chul Jung ; Wang-Cheol Zin ; Moonhor Ree
• 刊名：Macromolecules
• 出版年：2006
• 出版时间：August 8, 2006
• 年：2006
• 卷：39
• 期：16
• 页码：5385 - 5392
• 全文大小：477K
• 年卷期：v.39,no.16(August 8, 2006)
• ISSN：1520-5835

文摘

We synthesized two polyimides (PIs), poly(4,4'-(9,9-fluorenyl)diphenylene cyclobutanyltetracarboximide) (CBDA-FDA) and poly(4,4'-(9,9-fluorenyl)diphenylene pyromellitimide) (PMDA-FDA), and investigated in detail the surface morphology, molecular orientation, and nematic liquid crystal (LC) alignments ofrubbed CBDA-FDA and PMDA-FDA films. The rubbed CBDA-FDA film surface was found to containmicrogrooves that run parallel to the rubbing direction, but was found to induce LC alignment perpendicular tothe rubbing direction. In contrast, the rubbed PMDA-FDA film surface was found to contain unusual meanderingmicrogrooves that run perpendicular to the rubbing direction; this is the first report of such structures on a rubbedPI film. The PMDA-FDA film surface was found to induce LC alignment parallel to the rubbing direction. Eventhough these two PI films have quite different groove structures and LC alignment behaviors, the polymer mainchains in their surfaces lie in the film plane and are preferentially oriented along the rubbing direction, and thefluorenyl side groups lie in the out-of-plane and are preferentially oriented perpendicular to the rubbing direction.These LC alignment, anchoring energy, surface morphology, and polymer segmental orientation results indicatethat LC alignments on the surfaces of rubbed PI films are determined by the interplay between the directionallyanisotropic interactions of the LC molecules with the oriented polymer main chain segments, the oriented fluorenylside groups, and the microgrooves. The directionally anisotropic interactions of the LC molecules with the orientedpolymer chain segments were found to be much stronger than those with the directionally developed microgrooves.We conclude that CBDA-FDA and PMDA-FDA PIs are promising alignment layer materials for the fabricationof advanced LC display devices.