Rubbing-Induced Surface Morphology and Polymer Segmental Reorientations of a Model Brush Polyimide and Interactions with Liquid Crystals at the Surface
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- 作者：Seung Woo Lee ; Boknam Chae ; Byeongdu Lee ; Wooyoung Choi ; Seung Bin Kim ; Sang Il Kim ; Su-Moon Park ; Jin Chul Jung ; Kyung Hoon Lee ; and Moonhor Ree
- 刊名：Chemistry of Materials
- 出版年：2003
- 出版时间：August 12, 2003
- 年：2003
- 卷：15
- 期：16
- 页码：3105 - 3112
- 全文大小：311K
- 年卷期：v.15,no.16(August 12, 2003)
- ISSN：1520-5002
文摘
Poly{p-phenylene-3,6-bis[[4-(n-octyloxy)phenyl]oxy]pyromellitimide} (C8-PMDA-PDA PI),a model brush polymer with a fully rodlike backbone, was determined to be positivelybirefringent by prism coupling analysis. Films of the PI were examined in detail by opticalretardation and polarized infrared spectroscopy before and after mechanical rubbing with avelvet fabric. In addition, the alignment behavior of liquid crystal (LC) molecules in contactwith rubbed films of the model polymer was investigated. Atomic force microscopic imagingrevealed that rubbing caused microgrooves, as well as fine grooves (around 100 nm in size)with a surface morphology that resembled ground-beef, to develop parallel to the rubbingdirection. The morphologies of these grooves are attributed to the structure of the fabricfibers and the shear deformation characteristics of the polymer. At the rubbed surface, thepolymer main chains and the n-octyl end groups of the bristles were determined to be orientedparallel to the rubbing direction whereas the phenyloxy units of the bristles were found tobe oriented perpendicular to the rubbing direction. When LC molecules were placed in contactwith the rubbed PI films, the LC molecules formed a uniformly aligned structure with apretilt angle ranging from 25 to 87
along the rubbing direction, depending on the rubbingdensity. The tendency to form this structure was attributed to the favorable anisotropicinteractions of the LC molecules with the parallel reoriented polymer main chains and n-octylend groups of the bristles in the rubbed surface, as well as with the microgrooves and finegrooves aligned parallel to the rubbing direction. The large pretilt angles were favored despitethe relatively short alkyl side end group of the PI, which contains only half of the 16 carbonsgenerally required to achieve large pretilt angles of LCs. This result suggests that the n-octylend groups of the bristles play a critical role in the generation of large pretilt angles, mostlikely through favorable interactions between these groups and the aliphatic tails of the LCmolecules.
along the rubbing direction, depending on the rubbingdensity. The tendency to form this structure was attributed to the favorable anisotropicinteractions of the LC molecules with the parallel reoriented polymer main chains and n-octylend groups of the bristles in the rubbed surface, as well as with the microgrooves and finegrooves aligned parallel to the rubbing direction. The large pretilt angles were favored despitethe relatively short alkyl side end group of the PI, which contains only half of the 16 carbonsgenerally required to achieve large pretilt angles of LCs. This result suggests that the n-octylend groups of the bristles play a critical role in the generation of large pretilt angles, mostlikely through favorable interactions between these groups and the aliphatic tails of the LCmolecules.