title: The effect of junction modes between backbones and side chains of polyimides on the stability of liquid crystal vertical alignment.
abstract: Polyimides (PI-N9 and PI-N12) were synthesized from two kinds of functional diamines, whose junction modes between backbones and side chains were different. Side chains of PI-N9 were linked to the backbones with an ether bond spacer; and side chains of PI-N12 were directly linked to the backbones without any spacer. The PI alignment layer surfaces were investigated by atomic force microscopy, surface free energy measurements, X-ray photo-electron spectroscopy and polarized attenuated total reflection Fourier transformed infrared spectroscopy. It was found that PI-N9 lost the vertical alignment capability after high-strength rubbing, while PI-N12 could still induce liquid crystals (LCs) to align vertically under the same condition. The mechanism of the macroscopic molecular orientation of the PI surface is proposed. During the high-strength rubbing process, the side chain could rotate around the flexible ether bond which existed between the side chain and the main chain of PI-N9 and then fell over. Therefore, PI-N9 could not induce the vertical alignment of LCs anymore. But PI-N12 could keep LCs aligning vertically all the time, which proved that the stability of LC alignment induced by PI-N12 was better.
authors.affiliation: State Key Laboratory of Polymer Materials Engineering of China, College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, China. wang_yh@scu.edu.cn.
authors.forename: Xinyuan
authors.initials: X
authors.lastname: Che
authors.affiliation: State Key Laboratory of Polymer Materials Engineering of China, College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, China. wang_yh@scu.edu.cn.
authors.forename: Shiming
authors.initials: S
authors.lastname: Gong
authors.affiliation: State Key Laboratory of Polymer Materials Engineering of China, College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, China. wang_yh@scu.edu.cn.
authors.forename: Heng
authors.initials: H
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Polymer Materials Engineering of China, College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, China. wang_yh@scu.edu.cn.
authors.forename: Bin
authors.initials: B
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Polymer Materials Engineering of China, College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, China. wang_yh@scu.edu.cn.
authors.forename: Yinghan
authors.initials: Y
authors.lastname: Wang