Anisotropic Excluded Volume Effect and Alignment of Nematic Liquid Crystal in a Sandwich Cell

Okano, Kōji

doi:10.1143/jjap.22.l343

Cited by 62 publications

(36 citation statements)

References 6 publications

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“…Our results show that, for a rubbed polymer surface, a biaxial asymmetry exists on a molecular level. It is then reasonable to attribute the orientation of the LC, which is placed in contact with the oriented polymer surface, to an anisotropic interactions between the two systems, the dominant ones being the excluded volume interaction [28,30] arising from steric effects between the LC rods and the surface, and the intermolecular interaction [28,[31][32][33][34].…”

Section: Theory Of Lc Alignment: Maximum Overlap Modelmentioning

confidence: 99%

See 1 more Smart Citation

Liquid crystal alignment by rubbed polymer surfaces: a microscopic bond orientation model

Stöhr

Samant

1999

Journal of Electron Spectroscopy and Related Phenomena

189

134

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Section: Theory Of Lc Alignment: Maximum Overlap Modelmentioning

confidence: 99%

“…It has been shown that for a nematic LC consisting of rod-like units which is positioned on a clean, well-defined flat surface, the anisotropic part of the excluded volume interaction has the general form [30] DW ex Asin 2 a 30…”

Section: Theory Of Lc Alignment: Maximum Overlap Modelmentioning

confidence: 99%

Liquid crystal alignment by rubbed polymer surfaces: a microscopic bond orientation model

Stöhr

Samant

1999

Journal of Electron Spectroscopy and Related Phenomena

189

134

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“…[21] When the free surface is covered with a segregated layer, the excluded volume effect from the plane solid substrate should dominate. [22] An alternative explanation can be the tendency to adopt a planar orientation of the mesogenic groups in the segregated PBMA-b-PAz. [14b] It is noteworthy that the LC mesogens and MPS domain orientations in pure LC polymer films were unaffected by the surface energy of the substrate surface.…”

mentioning

confidence: 99%

Liquid‐Crystalline Polymer and Block Copolymer Domain Alignment Controlled by Free‐Surface Segregation

et al. 2013

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The surface effects and anchoring of liquid crystals (LCs) have long been significant concerns for material chemists and physicists.[1] The surface alignment of LCs by mechanical rubbing [2] is a widely recognized phenomenon and of particular significance in technological applications for display device fabrication.[3] Surface molecular orientations [4] and topographical grooves and undulations [5] of the substrate provide LC alignment effects. Furthermore, in the past two decades, the photoalignment of LCs on photoreactive polymer film surfaces by anisotropic irradiation [6] has become a significant method and an alternative to mechanical rubbing processes. The aligning substrates are not limited to polymer surfaces; various types of surfaces, such as hard inorganic materials [7] and soft bio-related interfaces, [8] can be used for the alignment induction. In addition to low-molecular-mass LCs, polymer LC materials are also aligned by the surface effect.[9] Despite the tremendous amount of accumulated knowledge and the number of potential applications, the surface alignment processes developed to date mostly involve manipulations on the surfaces of solid or condensed phases.Herein, we report on LC alignment alternation, which is attained by a modification of the free surface (air-film interface). The homeotropic surface anchoring effect and layer structuring at the free surface of calamitic LC molecules have been shown experimentally [10] and have been further verified by theoretical simulations.[11] To modify the free surface, the present approach adopts the surface segregation [12,13] of a small amount of a free-surface-active polymer. We demonstrate here that the coverage of the surface with the free-surface-active polymer leads to a homeotropic-to-parallel orientation change of LC mesogens, which further leads to an efficient in-plane photoalignment of microphase separation (MPS) domains of a relevant LC block copolymer by linearly polarized light (LPL).[14] With regard to the MPS alignment control, the important role of a top coat layer has recently been demonstrated by Bates et al. [15] In this case, a polar-to-nonpolar chemical conversion of the top layer is achieved to fulfill the requirement of spin-casting from an aqueous solvent and to provide a neutral (non-preferential) layer for the hydrophobic block copolymer during the annealing. In the present approach, in contrast, no additional coating procedure is required, providing a simple, versatile method for the desired alignment control of MPS domains.First, the alignment behavior of an LC azobenzene (Az) homopolymer (PAz in Figure 1 a; M n = 8.0 10 4 , M w /M n = 1.13, and g-43 8C-SmC-100 8C-SmA-120 8C-iso) was examined. A spincast film of PAz was prepared (thickness: 100-200 nm) from a chloroform solution. After annealing at 130 8C (above the isotropization temperature) for 10 min followed by gradual cooling via a smectic LC phase to room temperature, this film spontaneously formed the out-of-plane (perpendicular) orientation of Az side mesogens, a...

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“…In order to confirm the groove theory, a nanosized ultrafine pattern with a simple periodical shape is necessary for analysis and has not been investigated to date. [4][5][6][7][8][9][10] Therefore a nanosized pattern is interesting from the theoretical and practical points of view. However, LC alignment using nanosized and well-regulated patterns is not well understood.…”

Section: Introductionmentioning

confidence: 99%

Alignment of Nematic Liquid Crystal Molecules Using Nanometer-Sized Ultrafine Patterns By Electron Beam Exposure Method

Kagajyo¹,

Fujibayashi²,

Shimamura³

et al. 2005

Jpn. J. Appl. Phys.

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We have investigated the alignment of nematic liquid crystal (NLC) molecules using nanometer-sized ultrafine groove, tilted, and dot patterns fabricated by the electron beam exposure method. In order to improve the wetting condition of NLCs, we sputtered silicon dioxide on a substrate after the fabrication of ultrafine patterns. For a homogeneous alignment cell with an ultrafine groove pattern, an azimuthal anchoring energy of 2:84 Â 10 À4 J/m 2 was obtained. We also confirmed tilted and homeotropic alignments using tilted and dot patterns, respectively.

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Anisotropic Excluded Volume Effect and Alignment of Nematic Liquid Crystal in a Sandwich Cell

Abstract: It is shown that the orientation dependent excluded volume interaction between elongated nematic molecules and the cell walls always favors the planar alignment of nematic liquid crystals. For thermotropic liquid crystals the anchoring energy of this effect amounts to several erg/cm2.

Cited by 62 publications

References 6 publications

Liquid crystal alignment by rubbed polymer surfaces: a microscopic bond orientation model

Liquid crystal alignment by rubbed polymer surfaces: a microscopic bond orientation model

Liquid‐Crystalline Polymer and Block Copolymer Domain Alignment Controlled by Free‐Surface Segregation

Alignment of Nematic Liquid Crystal Molecules Using Nanometer-Sized Ultrafine Patterns By Electron Beam Exposure Method

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