Newly Synthesized Polyimide for Aligning Nematic Liquid Crystals Accompanying High Pretilt Angles

Fukuro, Hiroyoshi; Kobayashi, S.

doi:10.1080/00268948808081995

Cited by 57 publications

(14 citation statements)

References 5 publications

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“…It has often been demonstrated that the pretilt angle increases with decreasing surface energy and by introducing nonpolar groups, such as fluorine or alkyl groups, into the polyimide. Introduction of pretilt angle functionality into polyimide molecules can be achieved by long chain alkyl terminal chains, side chains, or main chains or by introducing fluorine atoms or modified diamines . Introduction of a bulky steroid structure has also been considered .…”

Section: Parameters That Define Lc Configurationmentioning

confidence: 99%

Alignment control technology of liquid crystal molecules

Ishihara

Mizusaki

2019

J Soc Info Display

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Liquid crystal displays are now indispensable in everyday life. The display characteristics considerably depend on the configuration of liquid crystal (LC) molecules and interactions between the LC molecules and an alignment film surface. In this paper, we introduce various methods to control parameters that dominate the LC alignment. These parameters include order parameters, the pretilt angle, the director direction, and surface anchoring strength. We also introduce their evaluation methods. In particular, recent alignment film‐free technology is explained in detail. In addition, details of how these parameters are related to the display characteristics, particularly wide viewing angles and fast response characteristics, are described primarily with reference to recent technologies.

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Section: Parameters That Define Lc Configurationmentioning

confidence: 99%

Alignment control technology of liquid crystal molecules

Ishihara

Mizusaki

2019

J Soc Info Display

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“…In order to optimize the performance of the LC device, this planar alignment should be accompanied by a nonzero so-called pretilt (8~), defined as the angle between the average molecular orientation in the bulk (the director) and the surface. Experimental realization and theoretical modeling of (high) pretilt angles with the use of rubbed polymer films has been reported frequently [2][3][4][5]. However, the generation of the pretilt on various substrates is not yet understood.…”

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confidence: 99%

Correlations between surface and bulk liquid-crystal alignment observed with optical second-harmonic generation

1992

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With the use of optical second-harmonic generation from liquid-crystal (LC) monolayers adsorbed on rubbed polymer surfaces, a close correlation between the rubbing-induced azimuthal orientational distribution of the LC monolayers and the resulting LC bulk pretilt angle has been observed. A simple model based on epitaxial growth of the bulk LC on top of the first LC monolayer is proposed to explain this correlation. PACS number(s): 61.30.v, 42.65. Ky, 68.35.8s Understanding the physical mechanisms involved in both surface and bulk liquid-crystal (LC) alignment is not only of fundamental interest but also finds its application in numerous electro-optic LC devices. Realization of a large-area monodomain LC layer sandwiched between two glass plates is a prerequisite for optimal performance of these devices. Homogeneous planar alignment (i.e. , parallel to the surface along some easy axis) of a LC layer can be achieved in several ways [1]. The most widely used technique is the rubbing of polymer-coated glass substrates. In order to optimize the performance of the LC device, this planar alignment should be accompanied by a nonzero so-called pretilt (8~), defined as the angle between the average molecular orientation in the bulk (the director) and the surface. Experimental realization and theoretical modeling of (high) pretilt angles with the use of rubbed polymer films has been reported frequently [2-5]. However, the generation of the pretilt on various substrates is not yet understood. Based on a theoretical model developed by Okano [6], Sugiyama et al. recently proposed a model for pretilted nematic LC layers on rubbed polyimide (PI) layers containing alkyl branches [5]. They correlated the polar 8~t o the azimuthal torsional surface coupling strength induced by the interaction of the bulk LC with the aligned alkyl branches at the surface.As a result of the pioneering work of Shen and coworkers on the use of optical second-harmonic generation (SHG) for the study of molecular orientations, the technique recently has been exploited as a surface analytical tool to investigate the LC-interface alignment [7][8][9][10][11][12][13][14]. No direct correlation has been observed between the polar angle of the first LC monolayer adsorbed on surfactantcoated glass substrates and the bulk pretilt [8,9]. Additionally it was shown that at the LC-PI interface a polar ordered LC monolayer exists, with an anisotropic azimuthal distribution, preferentially along the rubbing direction, even at temperatures well above the bulk nematicisotropic transition temperature [10,11]. It was also shown that both the LC monolayer and the LC director in the bulk are then aligned via short-range intermolecular interactions as opposed to long-range elastic interactions [10][11][12]. Combining these experimental results one con-eludes that the picture of a bulk LC, directly interacting with a flat polymer surface, with some distribution of aligned alkyl branches on top of it, seems no longer justified [5]. Instead, we have to consider the interaction o...

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“…The LC materials are anchored at the substrate along the preferred direction induced by the surface. Several alignment techniques have been reported in the literature [1][2][3][4]. The surface anchoring effect in nematic liquid crystals (NLCs) has been studied extensively from several decades to understand the precise interaction between the surface and LC materials [5,6].…”

Section: Introductionmentioning

confidence: 99%

Effect of Surface Anchoring on Optical Bistability in Deformed Helix Ferroelectric Liquid Crystal

Prakash

Choudhary

Mehta

et al. 2009

Molecular Crystals and Liquid Crystals

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The effect of surface anchoring on the optical bistability in deformed helix ferroelectric liquid crystal (DHFLC) has been investigated by electro-optical and textural methods. The threshold voltage studies have been carried out in strongly and weakly treated DHFLC cells. The long lasting memory effect has been observed in weakly treated DHFLC cells, which is due to minimization of depolarizing and ionic charges. Moreover, the response time has been shown to exhibit the dependence on the surface anchoring and the cell thickness. The informations obtained could be helpful for optimizing the parameters for memory devices based on DHFLC materials.

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Newly Synthesized Polyimide for Aligning Nematic Liquid Crystals Accompanying High Pretilt Angles

Cited by 57 publications

References 5 publications

Alignment control technology of liquid crystal molecules

Alignment control technology of liquid crystal molecules

Correlations between surface and bulk liquid-crystal alignment observed with optical second-harmonic generation

Effect of Surface Anchoring on Optical Bistability in Deformed Helix Ferroelectric Liquid Crystal

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