Thermal and Optical Stabilities of Photoisomerizable Polyimide Layers  for Nematic Liquid Crystal Alignments

Park, Byoungchoo; Jung, Youngyi; Choi, Hyun–Hee; Hwang, Ha-Keun; Kim, Youngkyoo; Lee, Sooman; Jang, Sei‐Hum; Kakimoto, Masa–aki; Takezoe, Hideo

doi:10.1143/jjap.37.5663

Cited by 82 publications

(19 citation statements)

References 18 publications

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“…The attachment of such fragments to a side chain increases the reaction rate and the photo-induced ordering. This position also increases the range of controllable LC pretilt angles [95]. The molecular mass of the photoaligning polymer also importantly affects photoalignment properties.…”

Section: Photo-degradation In Polyimide Filmsmentioning

confidence: 99%

“…The attachment of the fragments to a side chain increases the reaction rate and the photoinduced ordering. It also enables LC pretilt angles to be controlled over a wide range [95]. According to Akiyama et al's study [96], the attachment of azobenzene in the ortho position provides alignment with much greater photo-and thermal stability of the than that in the para position.…”

Section: Photo-crosslinking In Cinnamic Side-chain Polymersmentioning

confidence: 99%

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Photo-Alignment Technology

Lin

2014

Topics in Applied Physics

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LCDs are used in many everyday devices, including mobile phones, notebook computers and wide screen televisions. A typical LCD is composed of two glass substrates between which is a gap that is filled with LC. The arrangement of the LC is controlled by the boundary condition of an alignment film. A long-range orientational interaction causes the preferable alignment of a LC by the surface boundary to extend into the LC bulk. The alignment layer is typically rubbed with a special cloth to induce a unidirectional alignment of the LC. In the first devices based on twisted LCs, these LCs were aligned only by rubbing transparent electrodes. The rubbing technique became much more reliable when the glass substrate was covered with a rubbed polymer layer. The rubbing of polymers is a very simple technique and it is now extensively utilized in both small scientific laboratories and large LCD factories.Despite the extensive use of rubbing in LCD manufacturing, it has some serious shortcomings that arise from the contact involved in rubbing. These critically affect the production of the most recent generation of LCDs and miniature LC photonic devices. First, rotational rubbing for the polymer surface causes the accumulation of static charges and the formation of fine dust particles. The accumulation of static electricity may destroy the transistors or diodes in the LCD. The second shortcoming is the effect of decreasing in manufacturing yield. Rubbing for large and high-resolution active matrix LCDs (AMLCDs) involve additional difficulties that are associated with the precise control of the rubbing characteristics. Other problems are the difficulty of producing local structures with the required LC director alignment in the selected areas of the device. Finally, this method cannot be used to align LCs in closed volumes.For all of the above reasons, new alignment solutions and approaches are sought. There are some alternative methods of rubbing include laser writing, micro-rubbing, ion beam irradiation and photoalignment. Of these methods, the

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Section: Photo-degradation In Polyimide Filmsmentioning

confidence: 99%

Section: Photo-crosslinking In Cinnamic Side-chain Polymersmentioning

confidence: 99%

Photo-Alignment Technology

Lin

2014

Topics in Applied Physics

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“…However, main chain LC-type polymers (case b in Figure 4) also serve as fascinating photoalignment layers. Azobenzene, [84][85][86] stilbene, 87 cinnamate-type [88][89][90] and chalcone 91,92 functionalities have been introduced into polyester and polyimide main chain structures. In Figure 6, a few examples from these series are displayed.…”

Section: Photoresponsive Main Chain Lc Polymersmentioning

confidence: 99%

New strategies and implications for the photoalignment of liquid crystalline polymers

Seki

2014

Polym J

141

118

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The photoalignment of liquid crystalline materials has been studied extensively over the past two and a half decades and has recently become of technological importance in the liquid crystal display panel industry. This review introduces recent attempts at the photoalignment of liquid crystalline polymers and focuses on two aspects. First, strategies to ensure effective in-plane alignment of photoresponsive mesogens are highlighted. Despite the numerous investigations reported to date, film systems have not been well optimized in terms of realizing efficient photoreactions that consider the mesogen orientations. Second, new photoalignable systems composed of block copolymers with surface-grafted polymers and block copolymer films are introduced. The photoalignment processes in these mesoscopic systems involve strong cooperative motion of the different hierarchical size features. In the course of these approaches, a new strategic platform, photoalignment of liquid crystalline polymers via commanding from the free surface, is proposed. These approaches are expected to offer new concepts and possibilities for smart light-responsive materials and systems. Polymer Journal (2014) 46, 751-768; doi:10.1038/pj.2014.68; published online 13 August 2014 INTRODUCTIONPhotoreactions in ordered media have been the subject of numerous studies. In liquid crystal (LC) systems, molecules are packed with substantial motional freedom, and photoreactions trigger changes in the packing state or the collective molecular orientation. The effects can be amplified to the mesoscopic, microscopic and even macroscopic levels due to strong motional cooperativity. Photochromic reactions have frequently been incorporated in LC media because of their repeatability for controlling material properties. This approach has provided various types of smart, light-responsive materials 1 exhibiting surface-mediated photoalignment of LC materials, 2-6 photoinduced phase transitions, 7-12 photoorientation/addressing of polymer thin films, 13-18 photoinduced mass migrations, [19][20][21][22][23][24][25][26][27][28] phototactic sliding motions, 29-31 photo-driven motions and morphology of monolayers, 32-35 and macroscopic photomechanical deformations. [36][37][38][39][40][41][42][43][44][45][46] Photoalignment research and technology started in 1988 with the discovery of the reversible alignment control of nematic LCs by the photoisomerization of azobenzene on a substrate surface (Figure 1) by Ichimura et al. 47 It was demonstrated that the E/Z (trans/cis) photoisomerization of an azobenzene monolayer on a substrate can switch the alignment of nematic LC molecules between the homeotropic and planar modes. This active functional surface was dubbed a 'command surface' or 'command layer.' Shortly after this finding, Gibbons et al., 48 Dyadyusha et al. 49 and Schadt et al. 50 showed that angular selective excitation of an azo dye-doped polyimide or a photocrosslinkable polymer film with linearly

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“…Although rubbing is a simple and inexpensive method, it has many intrinsic drawbacks such as generation of electrostatic charges, contamination from rubbing debris and high temperatures (up to ca 250 1C). As alternatives to the rubbing process, noncontact methods such as photo-alignment [2][3][4][5] and ion-beam irradiation 6 have been used but they also have critical drawbacks associated with controlling the orientation of photoswitchs on the surface and low anchoring energies. 7 Indium-tin oxide (ITO) has been widely used as an electrode for LC display because of its low electrical resistance and high transmittance in the visible range of the optical spectrum.…”

Section: Introductionmentioning

confidence: 99%

Bifunctional ITO layer with a high resolution, surface nano-pattern for alignment and switching of LCs in device applications

et al. 2012

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We describe a novel method for liquid crystal (LC) alignment using nano-patterns of electrically conductive indium-tin oxide (ITO) layers with high resolution (cao 20 nm) and high aspect ratio (ca 10), fabricated based on the secondary sputtering phenomenon. The ITO pattern developed in this manner not only provides high anchoring energy comparable to that of rubbed polyimides, but also maintains its low resistivity as an electrode. As a result, the patterned ITO can function as an electrode and alignment layer at the same time, which facilitates successful fabrication of bifunctional conductive alignment layer for LC devices. The LC cells fabricated using patterned ITO substrates show highly stable alignment of LCs over large area and good electro-optical responses. Moreover, systematic approach made by the precise control of pattern dimensions allows us to estimate a critical anchoring energy required for an effective LC alignment based on Berreman's theory.

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Thermal and Optical Stabilities of Photoisomerizable Polyimide Layers for Nematic Liquid Crystal Alignments

Cited by 82 publications

References 18 publications

Photo-Alignment Technology

Photo-Alignment Technology

New strategies and implications for the photoalignment of liquid crystalline polymers

Bifunctional ITO layer with a high resolution, surface nano-pattern for alignment and switching of LCs in device applications

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