Measurement of Azimuthal Anchoring Energy  at Liquid Crystal/Photopolymer Interface

Li, Xiang Tong; Pei, Dong He; Kobayashi, Shunsuke; Iimura, Yasufumi

doi:10.1143/jjap.36.l432

Cited by 84 publications

(34 citation statements)

References 5 publications

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“…40 The molecularly oriented photoalignment layer based on photoreactive liquid-crystalline polymeric film 10 is reported to improve the azimuthal-anchoring energy due to the improved interaction between the LCs and oriented mesogenic side groups in the alignment layer. 41 Furthermore, polarizationselective photosensitization of cinnamate-containing polymeric films has been explored to improve the photosensitivity.…”

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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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“…The polymer films containing dimerized moiety of cinnamoyl group have been investigated as a photoalignment material by many researches. 2,[6][7][8][9][10] Schadt et al have obtained the alignment film by photodimerization of cinnamoyl group in the poly(vinyl 4-methoxycinnamate). LC molecules in the LC cell were aligned perpendicular to the electric vector of the incident LPUV light.…”

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confidence: 99%

Photoreaction of New Chalcone-Based Side Chain Type Liquid Crystalline Polymers and Alignment Behavior of Liquid Crystal on the Irradiated Films

Mutoh

Tsutsumi

Koide

2002

Polym J

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ABSTRACT:We investigated the photoreaction of the side chain type liquid crystalline polymers with a chalcone derivative in the side chain. The polymer films were irradiated with linearly polarized UV (LPUV) light (350 nm) under different conditions. The photodimerization of the chalconyl moieties would mainly occur due to a decrease in the peak assigned to the chalconyl moiety by UV-vis spectroscopy measurements. The extent of the photoreaction in the liquid crystalline (LC) state is larger than that in the solid state after spin-coating and in the locked-in LC state after annealing. The LC cell was fabricated from the polymer film irradiated with LPUV light to examine the alignment properties of low molar mass LC molecules on them. A mixture of low molecular liquid crystal with the dichroic dye was filled in the LC cell. The low molecular liquid crystal was easily aligned parallel to the electric vector of the incident exposed LPUV light in the LC cell with the polymer film irradiated in the LC state.KEY WORDS Chalcone / Liquid Crystalline Polymer / Photodimerization / Photoalignment / The alignment of liquid crystalline (LC) molecules plays an important role for liquid crystalline displays (LCDs). The rubbing process has been mainly employed for the uniaxial orientation of the LC molecules. However, the rubbing process has many disadvantages for LCDs such as generation of electrostatic charge and dust. Therefore, many methods of alignment technique for LC molecules are focused on rubbing free methods. Photoalignment procedure is recognized as one of rubbing free methods and is investigated as one of candidates that overcome the generation of electrostatic charge and dust for the rubbing process. 1,2 Photoalignment procedure is based on photochemical reactions such as photoisomerization, photodimerization (photocrosslinking) and photodecomposition. With respect to photoisomerization, polymers containing an azobenzene derivative were intensively investigated. [3][4][5] The reversible photoreaction of the azobenzene moieties in the polymer induced a reversible change in the alignment direction of low molecular weight LC molecules. Generally photodimerization of photosensitive groups in the polymer was employed to obtain a stable alignment of low molecular weight LC molecules.Photodimerization of the cinnamoyl chromophore in the polymer film have been studied in detail. The polymer films containing dimerized moiety of cinnamoyl group have been investigated as a photoalignment material by many researches. 2, 6-10 Schadt et al. have obtained the alignment film by photodimerization of cinnamoyl group in the poly(vinyl 4-methoxycinnamate). LC molecules in the LC cell were aligned perpendicular to the electric vector of the incident LPUV light. 6 Alignment behavior of LC molecules would be easily improved by the liquid crystalline polymer surface where mesogenic groups are aligned. Kawatsuki et al. had reported alignment properties of side chain type liquid crystalline polymers with the cinnamoyl groups as an alignmen...

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“…2,[6][7][8][9][10][11][12] It is desirable that photo-dimerization occurs by the exposure of relatively longer wavelength of the UV light to avoid partial degradation of polymers by the irradiation.…”

Section: 2mentioning

confidence: 99%

“…[3][4][5] Photo-dimerization of photosensitive groups in polymers is employed to obtain a stable alignment of LC molecules. 2,[6][7][8][9][10][11][12] It is desirable that photo-dimerization occurs by the exposure of relatively longer wavelength of the UV light to avoid partial degradation of polymers by the irradiation. 13 Photoreaction of chalcone moieties takes place by the irradiation with relatively longer wavelength of the UV light.…”

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Photo-alignment Properties of Main-Chain Liquid-Crystalline Polyimides Containing Chalcone Derivative

Mutoh

Nakao

Koide

2005

Polym J

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ABSTRACT:We investigated photo-alignment properties of main-chain polyimides prepared from acid anhydrides [4,4 0 -(hexafluoro-isopropylidene) diphthalic anhydride (6FDA) or 4,4 0 -biphthalic anhydride (BPDA)] and diamine derivatives containing a chalcone group. The polyimides in the film state were irradiated with linearly polarized UV (LPUV) light under different conditions. The liquid-crystalline (LC) cell was fabricated from the polyimide film irradiated with LPUV light. A mixture of a low molecular liquid crystal (4-cyano-4 0 -n-pentylbiphenyl: 5CB) and a dichroic dye was filled in the LC cell. 5CB in the LC cell was easily aligned perpendicular to the electric vector of the incident LPUV light. [DOI 10.1295/polymj.37.162] KEY WORDS Chalcone / Liquid-Crystalline Polymer / Photo-alignment / Polyimide / Alignment of liquid-crystalline (LC) molecules is important for liquid-crystalline displays (LCDs). Rubbing has been mainly employed for the uniaxial orientation of the LC molecules. However, rubbing has many disadvantages for LCDs such as generation of electrostatic charge and dust. Therefore, many methods of alignment technique for LC molecules focus on rubbing free methods. Photo-alignment procedure is a rubbing free method and is investigated as one of candidates that overcome the generation of electrostatic charge and dust for the rubbing process. 1,2The photo-alignment procedure is based on photochemical reactions such as photo-isomerization, photo-dimerization (photo-crosslinking) and photodecomposition.3-5 Photo-dimerization of photosensitive groups in polymers is employed to obtain a stable alignment of LC molecules. 2,[6][7][8][9][10][11][12] It is desirable that photo-dimerization occurs by the exposure of relatively longer wavelength of the UV light to avoid partial degradation of polymers by the irradiation.13 Photoreaction of chalcone moieties takes place by the irradiation with relatively longer wavelength of the UV light. Non-mesogenic photosensitive polymers containing chalcone derivatives have been studied for the photo-alignment film. 13-19The alignment of LC molecules is easily improved by the surface of LC polymers that exhibit a mesophase. This idea arises from the simple role of solubility for organic compounds, that is, like dissolves like. We already investigated thermal and photo-alignment properties of side-chain LC methacrylate polymers and side-chain polyimides bearing the chalcone derivative in the side chain. [20][21][22] Generally, main-chain polyimides demonstrate good thermal and mechanical properties based upon the rigid rod-like chemical structure of the polymer backbone. Therefore, main-chain polyimides would be suitable candidates for the polymeric materials applied to the photo-alignment film, because many polyimide derivatives have been used as an alignment film of LCDs owing to excellent thermal and mechanical properties.In this study, we investigate the extent of photoreaction of the chalcone-based main-chain polyimides prepared from two anhydride compounds [4,4 0 -(...

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Measurement of Azimuthal Anchoring Energy at Liquid Crystal/Photopolymer Interface

Cited by 84 publications

References 5 publications

Photoalignment and Photoinduced Molecular Reorientation of Photosensitive Materials

Photoalignment and Photoinduced Molecular Reorientation of Photosensitive Materials

Photoreaction of New Chalcone-Based Side Chain Type Liquid Crystalline Polymers and Alignment Behavior of Liquid Crystal on the Irradiated Films

Photo-alignment Properties of Main-Chain Liquid-Crystalline Polyimides Containing Chalcone Derivative

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