The Conformation of a Rubbed Polyimide

Meister, Roland; Jérôme, Bruno

doi:10.1021/ma980592u

Cited by 35 publications

(18 citation statements)

References 16 publications

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“…PI alignment layers are typically prepared from precursor solutions of poly(amic acid)s or PAEs, which are thermally imidized to polyimide layers and finally surface oriented by buffing [13,14,20]. To systematically study the effect of several experimental and structural parameters on the performance of alignment layers, these layers were incorporated in standardized LC guest-host cells, and the DR served as layer performance indicator.…”

Section: Basic Conceptsmentioning

confidence: 99%

Influence of Chain Stiffness and Preparation Methods on the Efficiency of Polyimide Alignment Layers for Liquid Crystal Orientation

Neuber

Giesa

Schmidt

2006

Molecular Crystals and Liquid Crystals

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In this work the influences of chain stiffness, solution concentration, and preparation methods on the formation and efficiency of highly oriented polyimide alignment layers are investigated. To quantify the performance of the alignment layers in liquid-crystalline (LC) cells, the orientation of a calamitic bis-azo dye in a lowmolecular-weight nematic LC guest-host mixture was employed. The degree of orientation was quantified by measuring the dichroic ratio (DR UV ) of the dye with polarized UV spectroscopy. Alignment layers were prepared from precursors of polyimide polymers with different chain stiffnesses. Additionally, the effect of polymer solution concentration, denoted as low (approx. 2 wt%) and high (50 wt%), and orientation techniques (casting and shearing) were systematically investigated. Cells assembled with buffed polyimide alignment layers originating from 1.5 wt% solutions in N-methyl-2-pyrrolidone (NMP) of a rigid para-linked poly(amic ethyl ester) precursor polymer resulted in a very high DR UV of 15. This value can be compared to values obtained with commercially available flexible polyimide layers, which had a DR UV of only 8. Pretilt angles of selected cells were also measured and were found to be in the range of 0.7 to 5.1 .

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Section: Basic Conceptsmentioning

confidence: 99%

Influence of Chain Stiffness and Preparation Methods on the Efficiency of Polyimide Alignment Layers for Liquid Crystal Orientation

Neuber

Giesa

Schmidt

2006

Molecular Crystals and Liquid Crystals

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“…(11) and using Eqs. (13) and (16) at threshold condition leads to the relationship between the threshold field and anchoring strength as the follows:…”

Section: ͑14͒mentioning

confidence: 99%

“…Then the anisotropic distribution of PI chains is responsible for the LC alignment. Surface molecular distribution of PI film treated by rubbing or photoexposure has been revealed through prominent experiments by several scientists [5][6][7][8][9][10][11][12][13]. Despite such experimental results, LC anchoring properties on rubbed surfaces that were considering surface distribution of PI molecules was reported by Baharat R. Acharya et al [14].…”

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confidence: 99%

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Dependence of threshold behavior upon surface distribution of polymer chains in a twisted nematic liquid crystal

et al. 2004

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On the basis of a general Rapini and Papoular equation and a unified surface anchoring energy theory, dependence of the threshold behavior of the liquid crystal director upon the statistical distribution of polyimide chains is theoretically investigated for a twisted nematic liquid crystal cell. We assumed that the anisotropy distribution of polyimide chains induced by the rubbing can be dominated by a Gaussian distribution around the rubbing direction. Our results show that the threshold behavior of a twisted nematic liquid crystal is affected strongly by the surface distribution of polymer chains.

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“…[1][2][3][4][5][6][7][8][9][10][11][12][13] The rubbing technology of the polyimide (PI) substrate is the most widely used alignment process for producing LC alignment layers, [14][15][16][17][18][19][20][21][22][23][24][25][26][27] which can induce planar or homeotropic alignment of LC cells by changing the molecular structure of the polyimide derivatives. In particular, polyimides with fluorinated groups have been studied widely to obtain homeotropic alignment layers.…”

Section: Introductionmentioning

confidence: 99%

Liquid crystal alignment properties of polystyrene derivatives containing fluorinated side groups

2010

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The liquid crystal (LC) alignment properties of a series of polystyrene derivatives containing various fluorinated side chain terminal moieties, such as 4-fluorophenoxymethyl, 3,4,5-trifluorophenoxymethyl, pentafluorophenoxymethyl, and 4-trifluoromethoxyphenoxymethyl groups, were investigated. These polymers could induce homeotropic and/or homogeneous planar LC alignment on their surfaces by changing the LC molecules and rubbing conditions. For example, when a positive (MJ001929 from Merck) and negative dielectric anisotropic LC mixture (MLC-7026-000 from Merck) were used, homeotropic LC alignment was observed in the LC cells made from unrubbed films of pentafluorophenoxymethyl-and 4-trifluoromethoxyphenoxymethyl-substituted polystyrenes with a smaller surface energy, whereas random planar LC alignment was observed in those made from the other polymers with a larger surface energy. On the other hand, homeotropic LC alignment behavior was observed in all the LC cells made from unrubbed films of all the polystyrene derivatives when 5CB was used as the LC material.

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The Conformation of a Rubbed Polyimide

Cited by 35 publications

References 16 publications

Influence of Chain Stiffness and Preparation Methods on the Efficiency of Polyimide Alignment Layers for Liquid Crystal Orientation

Influence of Chain Stiffness and Preparation Methods on the Efficiency of Polyimide Alignment Layers for Liquid Crystal Orientation

Dependence of threshold behavior upon surface distribution of polymer chains in a twisted nematic liquid crystal

Liquid crystal alignment properties of polystyrene derivatives containing fluorinated side groups

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