• Title/Summary/Keyword: Anchoring energy

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Improvement in the electro-optical properties of PDLCs (고분자 분산형 액정 표시소자의 전기광학적 특성 개선)

  • 최기석;박우상;박세근
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 1998.06a
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    • pp.125-128
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    • 1998
  • The electro-optical properties of PDLCs ( Polymer Dispersed Liquid Crystals ) that have been interested for applications to projection display devices lately are significantly improved. For this improvement, we optimized not only the material parameters of liquid crystal and polymer but also the process conditions. Using TL series liquid crystals and polymer PN393 provided from Merck, we obtained the optimized process conditions such as cell gap, LC concentration, curing temperature and curing time. Under these conditions, we have achieved PDLC cells of threshold voltage 2.6V. contrast ratio 260 and negligible hysteresis.

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The Alignment of Liquid Crystals on the Film Surfaces of Soluble Aromatic Polyimides Bearing t-Butylphenyl and Trimethylsilylphenyl Side Groups

  • Hahm, Suk-Gyu;Jin, Kyeong-Sik;Park, Sam-Dae;Ree, Moon-Hor;Kim, Hyung-Sun;Kwon, Soon-Ki;Kim, Yun-Hi
    • Macromolecular Research
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    • v.17 no.12
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    • pp.976-986
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    • 2009
  • With the study goal of firstly elucidating the anisotropic interactions between oriented polymer chain segments and liquid crystal (LC) molecules, and secondly of determining the contributions of the chemical components of the polymer segments to the film surface topography, LC alignment, pretilt, and anchoring energy, we synthesized three dianhydrides, 1,4-bis(4'-t-butylphenyl)pyromellitic dianhydride (BBPD), 1,4-bis(4'-trimethylsilylphenyl)pyromellitic dianhydride(BTPD), and 2,2'-bis(4"-tert-butylphenyl)-4,4',5,5'-biphenyltetracarboxylic dianhydride (BBBPAn), and a series of their organosoluble polyirnides, BBPD-ODA, BBPD-MDA, BBPD-FDA, BTPD-FDA, and BBBPAn-FDA, which contain the diamines 4,4'-oxydianiline (ODA), 4,4'-methylenediamine (MDA), and 4,4'-(hexafluoroisopropylidene)dianiline (FDA). All the polyimides were determined to be positive birefringent polymers, regardless of the chemical components. Although all the rubbed polyimide films exhibited microgrooves which were created by rubbing process, the film surface topography varied depending on the polyimides. In all the rubbed films, the polymer chains were unidirectionally oriented along the rubbing direction. However, the degree of in-plane birefringence in the rubbed film varied depending on the polyimides. The rubbing-aligned polymer chains in the polyimide films effectively induced the alignment of nematic LCs along their orientation directors by anisotropic interactions between the preferentially oriented polymer chain segments and the LCs. The azimuthal and polar anchoring energies of the LCs ranged from $0.45{\times}10^{-4}\;-\;1.37{\times}10^{-4}\;J/m^2$ and from $0.86{\times}10^{-5}\;-\;4.26{\times}10^{-5}\;J/m^2$, respectively, depending on the polyimides. The pretilt angles of the LCs were in the range $0.10-0.62^{\circ}$. In summary, the soluble aromatic polyimides reported here are promising LC alignment layer candidates for the production of advanced LC display devices.

Characteristics and Stability of Liquid Crystal Alignment for Interfacial Properties of Polyimide-Liquid Crystal (폴리이미드-액정 계면의 특성에 따른 액정 배향의 특성 및 안정성)

  • 동원석;이미혜;백상현
    • Polymer(Korea)
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    • v.27 no.5
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    • pp.484-492
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    • 2003
  • How the characteristics and stability of the rubbing-induced alignment of nematic liquid crystals (LCs) relate to the interfacial characteristics of LC-polyimide has been studied. The characteristics of the LC alignment (such as the LC texture, the pretilt angle, and the anchoring energy) and their thermal stability have been investigated for 5 polyimides synthesized for this work. The work showed that the rubbed polyimide alignment layer induces the strong LC anchoring and that the characteristics and stability of LC alignment are determined by the short-ranged interactions between LC and polyimide molecules at the alignment layer surface. The increased flexibility of the polyimide accelerates thermal imidization, increases the pretilt angle, and improves the alignment stability. It also turned out that fluorination of the polyimide tends to deteriorate the alignment uniformity and stability. No distinct differences in the alignment characteristics were shown for the aromatic- and alicyclic-dianhydride polyimides.

Electro-optical Characterization of Transmission Holographic PDLC with Surfactant

  • Woo, Ju-Yeon;Kim, Eun-Hee;Kim, Byung-Kyu
    • 한국정보디스플레이학회:학술대회논문집
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    • 2004.08a
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    • pp.1204-1207
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    • 2004
  • The effects of surfactant on the electro-optic properties of holographic polymer dispersed liquid crystal(HPDLC) have been studied hoping to increase the diffraction efficiency and to reduce the anchoring energy at interfaces. Octanoic acid(OA) was used as sulfactant. The 2,2,2 trifluoroethyl acrylate(TFEA) was added to the monomer mixture to enhance the phase separation and improve optical properties. The morphology of holographic gratings was examined using scanning electron microscopy(SEM). Addition of surfactant was likely to reduce the surface anchoring of the nematic droplet with the polymer surface which favors lowering of the swiching field and to improve the optical qualities.

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A Study on Fatigue Behaviors of RC Beams Strengthened with Carbon Fiber Sheets (CFS로 보강된 RC보의 피로거동에 관한 연구)

  • Park, Jeong-Yong;Cheung, Jin-Hwan;Kim, Seong-Do;Cho, Baik-Soon;Jang, Jun-Hwan
    • Proceedings of the Korea Concrete Institute Conference
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    • 2005.05a
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    • pp.35-38
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    • 2005
  • Carbon fiber sheets are widely used for strengthening the deteriorated RC structures. However most studies on the strengthening method of RC structures with carbon fiber sheets are concerning static problems. The purpose of this experimental study is to present the basic data on fatigue behaviors of. RC beams strengthened with carbon fiber sheets. The experimental parameters of this study are ; 1) the existence of U-shaped carbon fiber sheets at the ends for anchoring, 2) the number of carbon fiber sheet layers in strengthening the RC beams, 3) the load levels of $60\%\~90\%$ of the static bending moment strength, which is obtained form the static tests. Experimental results are estimated from the relationships of load level, displacement, number of repeated load and released energy. It is concluded that U-shaped carbon fiber sheets for end anchoring is very effective and the beams strengthened with one layer of carbon fiber sheet have longer fatigue life than that with three layers.

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Thermodynamic Control in Competitive Anchoring of N719 Sensitizer on Nanocrystalline $TiO_2$ for Improving Photoinduced Electrons

  • Lim, Jong-Chul;Kwon, Young-Soo;Song, In-Young;Park, Sung-Hae;Park, Tai-Ho
    • Proceedings of the Korean Vacuum Society Conference
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    • 2011.08a
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    • pp.68-69
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    • 2011
  • The process of charge transfer at the interface between two semiconductors or between a metal and a semiconductor plays an important role in many areas of technology. The optimization of such devices requires a good theoretical description of the interfaces involved. This, in turn, has motivated detailed mechanistic studies of interfacial charge-transfer reactions at metal/organic, organic/organic, and organic/inorganic semiconductor heterojunctions. Charge recombination of photo-induced electron with redox species such as oxidized dyes or triiodide or cationic HTM (hole transporting materials) at the heterogeneous interface of $TiO_2$ is one of main loss factors in liquid junction DSSCs or solid-state DSSCs, respectively. Among the attempts to prevent recombination reactions such as insulating thin layer and lithium ions-doped hole transport materials and introduction of co-adsorbents, although co-adsorbents retard the recombination reactions as hydrophobic energy barriers, little attention has been focused on the anchoring processes. Molecular engineering of heterogeneous interfaces by employing several co-adsorbents with different properties altered the surface properties of $TiO_2$ electrodes, resulting to the improved power conversion efficiency and long-term stability of the DSSCs. In this talk, advantages of the coadsorbent-assisted sensitization of N719 in preparation of DSSCs will be discussed.

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Study on seismic strengthening of railway bridge pier with CFRP and concrete jackets

  • Ding, Mingbo;Chen, Xingchong;Zhang, Xiyin;Liu, Zhengnan;Lu, Jinghua
    • Earthquakes and Structures
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    • v.15 no.3
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    • pp.275-283
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    • 2018
  • Seismic strengthening is essential for existing bridge piers which are deficient to resist the earthquake. The concrete and CFRP jackets with a bottom-anchoring method are used to strengthen railway bridge piers with low reinforcement ratio. Quasi-static tests of scaled down model piers are performed to evaluate the seismic performance of the original and strengthened bridge pier. The fracture characteristics indicate that the vulnerable position of the railway bridge pier with low reinforcement ratio during earthquake is the pier-footing region and shows flexural failure mode. The force-displacement relationships show that the two strengthening techniques using CFRP and concrete jackets can both provide a significant improvement in load-carrying capacity for railway bridge piers with low reinforcement ratio. It is clear that the bottom-anchoring method by using planted steel bars can guarantee the CFRP and concrete jackets to work jointly with original concrete piers Furthermore, it can be found that the use of CFRP jacket offers advantages over concrete jacket in improving the energy dissipation capacity under lateral cyclic loading. Therefore, the seismic strengthening techniques by the use of CFRP and concrete jackets provide alternative choices for the large numbers of existing railway bridge piers with low reinforcement ratio in China.

Microscopic Studies and Simulations of Bloch Walls in Nematic Thin Films

  • Park, Jung-Ok;Zhou, Jian;Srinivasarao, Mohan
    • 한국정보디스플레이학회:학술대회논문집
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    • 2005.07a
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    • pp.493-495
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    • 2005
  • The director profiles of the Bloch walls are directly visualized using fluorescence confocal polarizing microscopy. Both pure twist Bloch walls and diffuse Bloch walls are analyzed. Polar anchoring energy was measured from optical simulation of the transmitted light interference pattern or the fluorescence intensity profile of a pure twist wall..

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Liquid Crystal Alignment on Solid Substrates

  • Kim, Jae-Hoon;Shi, Yushan;Kumar, Satyendra
    • 한국정보디스플레이학회:학술대회논문집
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    • 2005.07a
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    • pp.755-758
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    • 2005
  • The mechanism responsible for liquid crystal (LC) alignment on solid substrates treated with mechanical rubbing or polarized UV is not understood. The results of x-ray reflectivity study of LC alignment on a large number of different alignment layers show that the anisotropy in the surface roughness of the substrate completely determines the LC alignment. The anchoring energy depends on the degree of roughness anisotropy and chemical interactions between the substrate and LC molecules.

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Azo-Dyes Photo-Aligning; Physics and Applications

  • Chigrinov, V.G.;Kwok, H.S.;Takada, Hirokazu;Takatsu, Haruyoshi
    • 한국정보디스플레이학회:학술대회논문집
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    • 2005.07a
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    • pp.759-763
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    • 2005
  • This review presents the status of our research in liquid crystal display (LCD) photo-aligning. We present the basic mechanisms of the photo-induced order in various photo-aligning materials and in azo-dye layers in particular and show that photo-aligning methods can provide a controllable pretilt angle and anchoring energy of the liquid crystal cell, as well as its high thermo and UV stability. The photo-aligning of various types of liquid crystal displays is also discussed.

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