NEXAFS studies on the rubbing effects of the surface structure of polyimides

Mori, Isamu; Araki, Tohru; Ishii, Hisao; Ouchi, Yukio; Seki, Kazuhiko; Kondo, K.

doi:10.1016/s0368-2048(96)80101-0

Cited by 20 publications

(10 citation statements)

References 4 publications

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“…An inclination of molecular units with respect to the sample surface has previously been observed for other polyimides by Ouchi and co-workers. 27,28 The authors rationalized their findings by assuming that the aromatic cores are assembled at the surface like shingles. This picture implicitly invokes the concept of a "quasi-epitaxial" interaction, where the aromatic cores of the liquid crystal molecules line up with the aromatic cores of the polyimide.…”

Section: Discussionmentioning

confidence: 93%

“…12 In previous NEXAFS experiments, Ouchi and coworkers have compared the surface orientation of two different homologous series of polyimides. 27,28 They found that the angular position of the X-ray absorption minimum deviated from normal incidence by several degrees. They derived a molecular picture of the near surface polymer conformation that correlates with the results of surface SHG and bulk tilt angle measurements.…”

Section: Introductionmentioning

confidence: 99%

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Molecular Orientation at Rubbed Polyimide Surfaces Determined with X-ray Absorption Spectroscopy: Relevance for Liquid Crystal Alignment

et al. 1998

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The molecular orientation at the surface of polyimide (PI) alignment layers used for liquid crystal displays has been determined using X-ray absorption spectroscopy (NEXAFS). The second moments of the orientation distribution function obtained from a detailed analysis reveal that, upon rubbing, the PI substrates develop biaxiality and an inclination of a few degrees. For a nematic liquid crystal (LC) in contact with these alignment layers, the pretilt angle was determined and revealed a weak correlation with buffing strength.

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Section: Discussionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Molecular Orientation at Rubbed Polyimide Surfaces Determined with X-ray Absorption Spectroscopy: Relevance for Liquid Crystal Alignment

et al. 1998

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“…Early proposals of the molecular orientation at the polymer surface were based on bulk-sensitive optical measurements. [6][7][8][9][10][11] Recently, surface-sensitive studies have been carried out using the near-edge X-ray absorption fine structure (NEXAFS) [12][13][14][15] and grazing incidence X-ray scattering (GIXS) 16 techniques. Both NEXAFS 15 and GIXS 16 studies on BPDA-PDA polyimide demonstrated the preferential near-surface alignment of polyimide chain segments along the rubbing direction, linking it to the preferred in-plane alignment direction of the LCs.…”

Section: Introductionmentioning

confidence: 99%

“…The origin of both the tilt direction, which for polyimide substrates is always found to point up into the rubbing direction, as shown in Figure 1, and the size of the tilt angle are of interest. Previous NEXAFS studies on BPDA-Cn and PMDA-Cn polyimides 12,14 linked the LC pretilt angle to a tilt angle of the aromatic building blocks at the polyimide surface. In another study the size of the pretilt angle has been explained in terms of the van der Waals interaction between the first LC monolayer and the polymer surface, independent of any asymmetry at the polymer surface.…”

Section: Introductionmentioning

confidence: 99%

Microscopic Origin of Liquid Crystal Alignment on Rubbed Polymer Surfaces

et al. 1998

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Surface-sensitive and polarization-dependent near-edge X-ray absorption fine structure (NEXAFS) measurements clearly reveal a preferred in-plane and out-of-plane orientation of phenyl and CO groups at the surface of rubbed polyimide films. The unidirectional molecular alignment at the surface is argued to provide the template for liquid crystal (LC) alignment of the films. Both the LC orientation along the rubbing direction as well as the direction of the out-of-plane LC pretilt are explained in a simple model. In this model the LC direction follows the preferential orientation of the phenyl rings at the surface. The preferred phenyl orientation is explained in terms of preferential chain segment alignment through a pulling action of the rubbing cloth fibers. The proposed LC alignment model is based on the existence of a statistically significant unidirectional bond asymmetry at the polymer surface, and it does not require the existence of crystalline order.

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“…Interestingly, poly-m-APM has been investigated by the Nagoya group with NEXAFS measurement. 20,21 While a correlation between shingling in the substrate and a pretilt could be very well established for a related compound, shingling was not found for poly-m-APM. These authors provided a picture which was not based on shingling.…”

Section: E Pretiltmentioning

confidence: 99%

Orientation of liquid crystal monolayers on polyimide alignment layers: A molecular dynamics simulation study

Vegt

Müller‐Plathe

Gelessus

et al. 2001

The Journal of Chemical Physics

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Detailed atomistic molecular dynamics simulations were performed on monolayers of 4Ј-n-octyl-4-cyanobiphenyl ͑8CB͒ adsorbed onto a surface of poly-m-alkanpyromellitimide ͑poly-m-APM͒, where m is the number of CH 2 units between the imide moieties. Poly-3-APM and poly-4-APM surfaces served as model surfaces to investigate the influence of microscopic grooves, polar carbonyl groups exposed to the surface, and an anisotropic van der Waals interaction between the liquid crystal ͑LC͒ molecules and the polymer chains. A Lennard-Jones fluid was chosen as the bulk phase in order to mimic the bulk LC phase. The fluid lubricates the motion of the LC molecules and increases the molecular tilt angle. While microgrooves dominate the alignment of isolated molecules, an anisotropic van der Waals interaction with the main chain is stronger in the case of entire monolayers.

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NEXAFS studies on the rubbing effects of the surface structure of polyimides

Cited by 20 publications

References 4 publications

Molecular Orientation at Rubbed Polyimide Surfaces Determined with X-ray Absorption Spectroscopy: Relevance for Liquid Crystal Alignment

Molecular Orientation at Rubbed Polyimide Surfaces Determined with X-ray Absorption Spectroscopy: Relevance for Liquid Crystal Alignment

Microscopic Origin of Liquid Crystal Alignment on Rubbed Polymer Surfaces

Orientation of liquid crystal monolayers on polyimide alignment layers: A molecular dynamics simulation study

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