• Title/Summary/Keyword: Nematic liquid crystal

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A study on Electro-Optical Characteristics of the UV Aligned FFS Cell on the Organic Layer (유기막에 UV 배향한 FFS 액정셀의 전기광학특성)

  • Han, Jeong-Min;Hwang, Jeoung-Yeon;Kim, Byoung-Yong;Han, Jin-Woo;Kim, Jong-Hwan;Lee, Sang-Keuk;Oh, Yong-Cheul;Seo, Dae-Shik
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2006.11a
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    • pp.278-279
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    • 2006
  • In this study, we investigated the electro-optical (EO) characteristic of fringe-field switching (FFS) mode cell by the two kinds of ultraviolet (UV) alignment method on the organic thin film (polyimide Pl). The suitable organic layers for FFS cell and the aligning capabilities of nematic liquid crystal (NLC) using the in-situ photo-alignment method were studied. An unstable V-T curve of UV-aligned FFS-LCD with conventional photo-alignment method can be achieved. However, a stable V-T curve of UV-aligned FFS-LCD with in-situ photo-alignment method (1h), and V-T curve of UV-aligned FFS-LCD with in-situ photo-alignment method was much stable comparing with that of other UV-aligned FFS-LCD's, As a result, more stable EO performance of UV-aligned FFS-LCD with in-Situ photo-alignment method is obtained than that of the other UV-aligned FFS-LCD's.

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Liquid Crystal Alignment Effect and Electro-Optical Characteristics of TN-LCD on a-C:H Thin Films (a-C:H 박막을 이용한 액정 배향 효과 및 TN-LCD 의 전기광학 특성)

  • Hwang, Jeong-Yeon;Jo, Yong-Min;Rho, Soon-Jun;Baik, Hong-Koo;Seo, Dae-Shik
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2002.11a
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    • pp.124-127
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    • 2002
  • LC aligning capabilities and the variation of pretilt angles with ion beam irradiation on the a-C:H thin films, and electro-optical (EO) performances of the ion beam aligned twisted nematic (TN)-liquid crystal display (LCD) with oblique ion beam exposure on the a-C:H thin film were studied. A high pretilt angle of $3.5{^{\circ}}$ via ion beam irradiation on the a-C:H thin film was measured. Also, the LC pretilt angle decreased due to the increase in surface roughness at over 2 min of IB exposure time. It is considered that this roughness increase due to increasing IB exposure time that generated destroy of oriented rings of atoms related to LC alignment. An excellent voltage-transmittance (V-T) curve of the ion beam aligned TN-LCD was observed with oblique ion beam exposure on the a-C:H thin film for 1 min. Also, a faster response time for the ion beam aligned TN-LCD with oblique ion beam exposure on the a-C:H thin film for 1 min can be achieved. Finally, the residual DC property of the ion beam aligned TN-LCD with ion beam exposure of 1 min on the a-C:H thin film is almost same as that of the rubbing aligned TN-LCD on a PI surface.

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Novel optical representation of binary data to improve the beam intensity uniformity at the recording plane in the storage of Fourier holograms of digital data (디지털 데이터의 Fourier 홀로그램 저장에서 기록면의 빔세기 균일도 향상을 위한 2진 데이터의 새로운 광학적 표현)

  • 장주석;신동학;오용석
    • Korean Journal of Optics and Photonics
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    • v.12 no.4
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    • pp.339-344
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    • 2001
  • We propose a method to represent binary data by modulating both the intensity and the phase of uniform plane waves with a twisted-nematic liquid crystal display for holographic digital data storage especially in a disk-shaped recording medium. As far as intensity modulation is concerned, our method is not different from the conventional method, because binary bit values 0 and 1 are represented by the dark (off) and lit (on) states of the liquid crystal display pixels, respectively (or vice versa). With our method, however, the on pixels are also controlled so that the beams passing through them can have one of two different phase delays. If the difference of the two phase delays is close to 180 degrees, we can reduce the dc component of the data image and thus improve the beam intensity uniformity at the holographic recording plane when Fourier plane holograms are recorded. The feasibility of our method is experimentally demonstrated. rated.

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Characteristic Analysis of Vertical Alignment by Ion-beam Irradiation Angle and Energy Density (이온빔 조사 각도와 에너지강도에 의한 수직 배향막의 특성 분석)

  • Kang, Dong-Hun;Oh, Byeong-Yun;Kim, Byoung-Yong;Han, Jin-Woo;Kim, Young-Hwan;Ok, Chul-Ho;Han, Jeong-Min;Lee, Sang-Keuk;Seo, Dae-Shik
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2007.11a
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    • pp.398-398
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    • 2007
  • The Liquid Crystal (LC) alignment uniformity is very important in LC devices. The alignment mechanism of LC molecules on a rubbed polyimide (PI) surface is very important for both LC fundamental research and application. So, Generally a rubbing method to align LC has been widely used to mass-produce LCD panels. But because rubbing method is contact method between rubbing fabric and indium-tin-oxide glass or flexible substrate, rubbing method has some defects, such as the electrode charges and the creation of contaminating particles. Thus we strongly recommend a non-contact alignment technique for getting rid of some defects of rubbing method. Most recently, the LC aligning capabilities achieved by ion-beam exposure on the organic and nonorganic thin film surface have been reported successfully. In this research, we studied the tilt angle generation and electro-optical performances for a NLC on homeotropic polyimide surfaces with ion-beam exposure. The LC aligning capabilities of a nematic liquid crystal (NLC) on a homeotropic PI surface using a new ion-beam method were studied. On the homeotropic PI surface, the tilt angle of the NLC by exposure ion-beam had a tendency to decrease as increased ion-beam energy density. And, on the homeotropic PI surface, the alignment character of the NLC with respect to ion-beam energy was good. And we achieved satisfactory result for EO character.

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Study on Rheological Properties of HBA/HNA Thermotropic Liquid Crystalline Polymer (HBA/HNA계 열방성 액정고분자의 유변학적 특성에 관한 연구)

  • Son, Young-Gon
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.11 no.12
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    • pp.5216-5220
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    • 2010
  • Rheological measurement of a thermotropic liquid crystalline poymer (TLCP) is not an easy task since their rheological responses are strongly influenced by a thermal history during a processing and thus the reproducibility of the measurement is poor. In order to find out a cause for the strong influence of the thermal history, rheological measurements and DSC observations of the TLCP having various thermal histories were carried out. It was observed that the TLCP used in this study shows liquid-like behavior at a temperature above a crystal-nematic transition temperature ($280^{\circ}C$), but at the same time crystallization can occur at this temperature range and as a consequence the viscosity of the polymer continuously increases. When the samples are heated beyond the $320^{\circ}C$, all crystals thus formed and the thermal histories were observed to disappear. Crystallization rate of the samples annealed above $320^{\circ}C$ was very low at even the lowed temperature ($280^{\circ}C\;{\sim}\;320^{\circ}C$). Therefore, it is concluded that rheological measurements of TLCP used in this study must be performed after annealed above the nematic-isotropic transition temperature for better reproducibility.

Synthesis and Characterization of Polyamide Having Photoreactive Group in the Backbone and its Liquid Crystal Aligning Property (광반응성 작용기를 주사슬에 갖는 폴리아미드의 합성과 특성 분석 및 액정분자의 배향 특성)

  • Jung, Eun-Young;Lee, Tae-Jin;Lee, Seung-Woo
    • Polymer(Korea)
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    • v.35 no.4
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    • pp.350-355
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    • 2011
  • A soluble polyamide containing photosensitive l,4-phenylenediacrylic acid (PDA) in main chain with biphenyl moiety was synthesized. The chemical structure of synthesized polyamide was investigated by means of $^1H$ NMR spectroscopy. The polymer was stable up to $280^{\circ}C$ and soluble in organic solvents, giving a good quality of thin films. The photoreaction of unpolarized LTV irradiated films was investigated by means of UV-vis absorption spectroscopy and FTlR spectroscopy, and liquid crystals (LCs) alignment property was examined by exposing to linearly polarized UV light (LPUVL) of 260~380 nm. The polyamide in film has excellent photoreactivity to unpolarized UV light. Direction selective photoreaction of PDA moiety in Lhe film was found to further induce nematic liquid -crystals to align along a perpendicular direction with respect to the electric vector of LPUVL, regardless of exposure energy of LPUVL. In addition, pretilt angle was measured by means of crystal rotation method. LPUVL-exposed polymer film induced the alignment of liquid-crystals (LC) with a pretilt angle of 0.2~$0.5^{\circ}$.

Synthesis and Characterization of Polymers with Azobenzene and Hexamethylene Groups in Main Chain (주사슬에 아조벤젠기와 헥사메틸렌기를 갖는 고분자의 합성 및 특성)

  • Gu, Su-Jin;Lee, Eung-Jae;Bang, Moon-Soo
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.20 no.4
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    • pp.86-92
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    • 2019
  • Polymers with various compositions of azobenzene and hexamethylene groups in the main chain were synthesized by a Schotten-Baumann reaction and their properties were investigated. The chemical structures and physical properties of the synthesized polymers were investigated by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, differential scanning calorimetry, thermogravimetric analysis, polarized optical microscopy, and x-ray diffraction. The polymers showed an inherent viscosity of 1.28-1.36 dl/g and were relatively insoluble in most organic solvents. The melt transition temperature increased rapidly with increasing number of azobenzene groups in the polymer. When the azobenzene monomer content was more than 50 mol%, no melting transition occurred below the decomposition temperature. Among the polymers with a melt transition temperature, the MP-A3C7 and MP-A5C5 polymers were liquid crystalline materials and exhibited a nematic phase with weak liquid crystallinity over a wide liquid crystal temperature range. This difference in the properties of the synthesized polymers is likely due to the changes in intermolecular forces resulting from the linearity and polarity of the trans-form of azobenzene.

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.

Electro-optical (EO) characteristics of photo-aligned TN-LCD on PM4Ch surfaces (PM4Ch 표면을 이용한 광배향 TN-LCD의 전기광학특성)

  • Hwang, Jeoung-Yeon;Park, Sang-Gun;Park, Tae-Kyu;Seo, Dae-Shik;Suh, Dong-Hack
    • Proceedings of the KIEE Conference
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    • 1999.07d
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    • pp.1765-1767
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    • 1999
  • We synthesised a photo-alignment material of PM4Ch (poly(4-methacryloylloxychalcone)). The electro-optical (EO) characteristics of photo-aligned twisted nematic (TN)-liquid crystal display (LCD) with linearly polarized ultraviolet (UV) light irradiation on PM4Ch surface were investigated. The uniform alignment of NLC with polarized UV light irradiation on PM4Ch surface was measured. Also, We had The excellent voltage-transmittance characteristics of photo-aligned TN-LCD. The low threshold voltage of photo-aligned TN-LCD was measured. Moreover, the fast response time of photo-aligned TN-LCD on PM4Ch was successfully achieved. Finally The reduction DC voltage of photo-aligned TN-LCD decreases with increasing the UV light irradiation time on photo-dimerized PM4Ch surface.

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Electro-Optical Characteristics of the Ion-Beam-Aligned FFS-LCD on a Diamond-like-Carbon Thin Film

  • Hwang, J.Y.;Park, C.J.;Seo, D.S.;Jeong, Y.H.;Kim, K.C.;Ahn, H.J.;Baik, H.K.
    • 한국정보디스플레이학회:학술대회논문집
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    • 2004.08a
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    • pp.1132-1136
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    • 2004
  • In this paper, we intend to make FFS mode cell with LC alignment used non-rubbing method, ion beam alignment method on the a-C:H thin film, to analyze electro-optical characteristics in this cell. We studied on the suitable inorganic thin film for FFS-LCD and the aligning capabilities of nematic liquid crystal (NLC) using the new alignment material of a-C:H thin film as working gas at rf bias condition. A high pretilt angle of about 5$^{\circ}$ by ion beam(IB) exposure on the a-C:H thin film surface was measured. An excellent voltage-transmittance (V-T) and response time curve of the ion-beam-aligned FFS-LCD was observed with oblique ion beam exposure on the DLC thin films.

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