A Model of the Unidirectional Alignment Accompanying the Pretilt Angle of a Nematic Liquid Crystal (NLC), 5CB, Oriented on Rubbed Organic-Solvent-Soluble Polyimide Film

Nishikawa, Michinori; Bessho, Nobuo; Natsui, T.; Ohta, Yoshihisa; Norihiro, Yoshida; Seo, Dae Shik; Iimura, Yasufumi; Kobayashi, Shunsuke

doi:10.1080/10587259608034058

Cited by 33 publications

(5 citation statements)

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“…This suggests the importance of knowing the molecular orientation and chemical structure of the polyimide surfaces. Most of the studies rely on bulk-sensitive methods such as infrared dichroism and optical retardation [9][10][11][12][13][14][15] . Recently, some surface-sensitive measurements using electron spectroscopy for chemical analysis 16) and X-ray scattering to obtain molecular orientation and structure 17,18) of polyimide surfaces have been reported.…”

Section: Introductionmentioning

confidence: 99%

Surface studies of polyimide thin films via surface-enhanced Raman scattering and second harmonic generation

Xue

et al. 1998

Macromol. Rapid Commun.

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Two polyimides having the same backbone chemical structure and different pendant side groups at the 2-and 29-positions of the diamine, the six methylene units capped with 4-cyanobiphenyl end groups and trifluoromethyl, were synthesized (6FDA-6CBO and 6FDA-PFMB). Surface-enhanced Raman scattering and surface optical second harmonic generation measurements show that after rubbing the major change in 6FDA-PFMB surface appears in the orientation of the dianhydride, which was originally planar, but becomes tilted with respect to the surface plane. In the case of 6FDA-6CBO, rubbing also causes the originally planar 4-cyanobiphenyls to tilt away from the surface and assume an azimuthally anisotropic distribution.

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Section: Introductionmentioning

confidence: 99%

Surface studies of polyimide thin films via surface-enhanced Raman scattering and second harmonic generation

Xue

et al. 1998

Macromol. Rapid Commun.

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“…7͒. 18 The optical axis of PI-1 is aligned along the polymer backbone. On the other hand, the fluorene unit in PI-2, which has a large birefringence, is aligned perpendicular to the axis of the main chain.…”

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confidence: 99%

Mechanism of unidirectional liquid-crystal alignment on polyimides with linearly polarized ultraviolet light exposure

Nishikawa

Taheri

West

1998

Applied Physics Letters

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116

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Unidirectional liquid-crystal ͑LC͒ alignment by a linearly polarized ultraviolet light ͑UV͒ exposure was examined using two types of polyimide ͑PI͒. PI with a fluorene unit incorporated in a side chain showed LC alignment perpendicular to those of conventional PIs, i.e., perpendicular to the rubbing direction and parallel to the exposure polarization of UV. The results of the dichroic ratio measurement of LC cells, UV absorption spectra, birefringence, infrared absorption spectra, and PI conformation calculations using molecular mechanics suggest that the photodecomposition of PI by UV exposure produces anisotropic van der Waals forces, which align LC along its optical axis.

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“…For a given type of cloth this is correlated to the force applied to the polyimide surface and therefore characterizes the strength of rubbing. More information about the effect of the rubbing parameters can be found in the literature. ,, The pile impression for these experiments was varied between 0 ≤ p ≤ 0.4 mm while keeping all other parameters of the rubbing process constant.…”

Section: Experiments and Resultsmentioning

confidence: 99%

“…The effect of rubbing on the polyimide is not yet fully clear. It is believed that an alignment of the polymer chain parallel to the rubbing direction takes place. − In this respect, rubbing would be similar to stretching of a polymer film, which also leads to an alignment of the polymer chains. This can be concluded from the observed birefringence of polymer surfaces 4,6 after rubbing.…”

Section: Introductionmentioning

confidence: 99%

The Conformation of a Rubbed Polyimide

Meister

Jérôme

1998

Macromolecules

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We report second harmonic generation (SHG) measurements of rubbed and unrubbed surfaces of the fluorinated main-chain polyimide PMDA/BDAF made from pyromellitic dianhydride (PMDA) and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (BDAF). Such rubbed polymers are commonly used as alignment materials for the nematic phases of liquid crystal display cells (LCD), although the rubbing process itself is not yet well understood. The SHG results are used to construct the full orientational distribution function of the noncentrosymmetric part of the polymer. This allows us to determine the preferred conformations of the polyimide at the surface and gives insight into the conformational changes of the polymer during rubbing.

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A Model of the Unidirectional Alignment Accompanying the Pretilt Angle of a Nematic Liquid Crystal (NLC), 5CB, Oriented on Rubbed Organic-Solvent-Soluble Polyimide Film

Cited by 33 publications

References 18 publications

Surface studies of polyimide thin films via surface-enhanced Raman scattering and second harmonic generation

Surface studies of polyimide thin films via surface-enhanced Raman scattering and second harmonic generation

Mechanism of unidirectional liquid-crystal alignment on polyimides with linearly polarized ultraviolet light exposure

The Conformation of a Rubbed Polyimide

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