Stabilization of liquid crystal photoaligning layers by reactive mesogens

Yaroshchuk, O.; Kyrychenko, V.; Du, Tao; Chigrinov, Vladimir G.; Kwok, Hoi Sing; Hasebe, Hiroshi; Takatsu, Haruyoshi

doi:10.1063/1.3168526

Cited by 60 publications

(33 citation statements)

References 9 publications

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“…64,65 Polymethacrylate with amide side groups 27 and polyamide 28 are also active for the LC photoalignment. 66,67 Furthermore, liquid-crystalline polymer 29 shows an axis-selective photo-Fries rearrangement of the benzoate side groups followed by thermally amplified molecular reorientation, and the resultant film has an LC alignment ability. 68 In this case, the LC alignment direction depends on the exposure energy and type of end substituent groups.…”

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confidence: 99%

Photoalignment and Photoinduced Molecular Reorientation of Photosensitive Materials

Kawatsuki¹

2011

Chemistry Letters

116

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Photosensitive materials for photoalignment of liquid crystals (LCs) and photoinduced molecular reorientation are described, especially focusing on azobenzene-containing materials and photocrosslinkable polymers. All the materials generate photoinduced optical anisotropy by means of linearly polarized (LP) light exposure. The large optical anisotropy is induced when the axis-selective photoreaction is accompanied by molecular reorientation. Ç IntroductionDue to practical applications of the alignment layer of functional materials such as low-molecular-weight liquid crystals (LCs), photoalignment and photoinduced molecular reorientation of photosensitive films have received much attention. 13 Additionally, these films have been investigated for molecularly oriented birefringent devices due to the absence of mechanical damage, absence of electric charge, and patterning ability.13 Photoinduced optical and physical anisotropies can be generated in a photoreactive polymeric film by light exposure because the photoreaction changes the inherent refractive index of the molecules. Irradiating with linearly polarized (LP) light causes the photosensitive molecules parallel to the polarization (E) of LP light (y axis) to preferentially photoreact (Figure 1). This axis-selective photoreaction leads to optical anisotropy (birefringence) between the y axis and xz plane if the photoreaction changes the inherent refractive indices of the molecules.To obtain uniaxial alignment of LCs on thin polymeric films, the LC photoalignment layer should exhibit optical or physical anisotropy. Under this circumstance, a large molecular orientation of the film is unnecessary. The anisotropic interaction between the photoalignment layer and LC molecules induces uniaxially oriented LC molecules.1 Because the axis-selective photoreaction induces a small change in the refractive index of the photoalignment layer, 4 a thick film is necessary for optically anisotropic devices such as a birefringent film. Consequently, a large optical anisotropy in the photoreacted film is generated when molecular reorientation occurs during an anisotropic photoreaction. 3Various types of materials that undergo an axis-selective photoreaction to generate photoinduced optical anisotropy have been investigated, including azobenzene-containing polymers 2,57 and photocrosslinkable polymers. 1,3,4 For the azobenzene molecules, axis-selective photoisomerization is generated when the film is irradiated with linearly polarized (LP) light (Figure 2a). Similarly, irradiating with LP ultraviolet (LPUV) light induces both axis-selective [2 + 2] photo/cycloaddition (photocrosslinking) reaction and photoisomerization for cinnamic ester derivatives (Figure 2b). Low-molecular LC molecules easily align on these anisotropically photoreacted films. When an axis-selective photoreaction occurs without generating molecular reorientation, the photoinduced birefringence (¦n) is less than 0.01. 4 An anisotropic photoreaction combined with molecular motion may generate a large optica...

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confidence: 99%

Photoalignment and Photoinduced Molecular Reorientation of Photosensitive Materials

Kawatsuki¹

2011

Chemistry Letters

116

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“…To solve the problems, photo alignment which has non-contact type has been developed [7][8][9][10][11][12]. This can provide the excellent order parameter for high quality image of the LCDs.…”

Section: Introductionmentioning

confidence: 99%

High Speed In-Plane Switching Liquid Crystal Cell by Using Photo Alignment Method

Mun

Cho

Lee³

et al. 2015

Molecular Crystals and Liquid Crystals

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We proposed a fast response time in-plane swithcing (IPS) liquid cryatal (LC) mode in the photo-alignment layer. In order to achieve the fast response time, we first enhanced the anchoring energy of the photo-alignment layer by coating the reactive mesogens (RMs) which can modify the surface condition and also applied the low cell property in the LC cell by using the positive A-plate with same effective retardation as the LC layer.In the experiments, we demonstrated that the coated RM layer can make the strong surface anchoring energy because of its strong polymer chain by the UV exposure and also confirmed the improved response time in the low cell gap IPS cell. As measured results, the response time of the proposed IPS LC cell could be improved over 56.86% and 62.18% compared with that of a conventional photo-aligned IPS cell with/without RM coating, respectively because of the low cell gap property.

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“…[15][16][17] In order to overcome these limitations, the current photoaligning materials [18][19][20][21][22][23][24] need to be further improved. The recently introduced polymer-surface stabilisation by reactive mesogen (RM) [25,26] and photoaligning stabilisation [27][28][29][30][31] can be promising candidate methods for the enhancement of surface anchoring. Nevertheless, the switching stability of electro-optic characteristics of photoaligned IPS LCD with electric field stress still needs to be improved.…”

Section: Introductionmentioning

confidence: 99%

Reducing driving voltage and securing electro-optic reliability of in-plane switching liquid crystal display by applying polysulfone photoalignment layer with photo-reactive mesogens

et al. 2014

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2014) Reducing driving voltage and securing electro-optic reliability of in-plane switching liquid crystal display by applying polysulfone photoalignment layer with photo-reactive mesogens, Liquid Crystals, 41:8, 1057-1064, Newly synthesised photocurable polysulfone (PSCMh) was applied as a photoalignment layer of in-plane switching liquid crystal display (IPS LCD). When the linear polarised ultraviolet light (LPUVL) was irradiated on the typical calamitic nematic liquid crystals on the PSCMh alignment layer, the liquid-crystal director was aligned perpendicular to the LPUVL. Based on the experimental results, it was realised that IPS LCD photoaligned by PSCMh with additional polymer layer associated with reactive mesogen (RM) showed a low driving voltage with reduction of 0.2 V compared to the rubbed cell and also excellent electro-optic reliability such as alignment stability, residual direct current and voltage holding ratio compared to the purely photoaligned cell. Therefore, it was concluded that the polymer stabilisation of PSCMh with RM was effective for improving IPS LCD performances.

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Stabilization of liquid crystal photoaligning layers by reactive mesogens

Abstract: Photoalignment effect in a liquid-crystal film doped with nanoparticles and azo-dye Appl.In-plane order of liquid crystal molecules adsorbed on photoaligned polyimide films: Coverage dependence in submonolayer range

Cited by 60 publications

References 9 publications

Photoalignment and Photoinduced Molecular Reorientation of Photosensitive Materials

Photoalignment and Photoinduced Molecular Reorientation of Photosensitive Materials

High Speed In-Plane Switching Liquid Crystal Cell by Using Photo Alignment Method

Reducing driving voltage and securing electro-optic reliability of in-plane switching liquid crystal display by applying polysulfone photoalignment layer with photo-reactive mesogens

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