• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 D
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• pp.1258-1260
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• 1998

In this study, we investigated the generation of pretilt angle for nematic liquid crystal (NLC) in a cell with oblique non-polarized ultraviolet (UV) light irradiation on polyimide (PI) surfaces. It was found that the monodomain alignment of the NLC is obtained with an angle of incidence of $70{\sim}85^{\circ}$ on PI surface. We consider that the monodomain alignment of NLC is attributed to anisotropic dispersion force due to photo-depolymerization of polymer on PI surfaces. Also, pretilt angle of NLC is generated about $3^{\circ}$ with an angle of incidence of $70{\sim}75^{\circ}$. It is considered that the pretilt angle generation in NLC is attributed to interaction between the LC molecules and the polymer surfaces.

• 폴리머
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• 제34권1호
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• pp.32-37
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• 2010

액정표시소자의 광배향막으로 적용하기 위하여 올리고머 신나메이트와 폴리(비닐 신나메이트) (PVCi)의 블렌드를 이용하여 그루브 패턴을 형성하고 광배향 특성을 관찰하였다. UV-vis 스펙트럼 분광계를 이용하여 자외선 조사 시간에 따른 광반응 속도를 평가한 결과 올리고머 신나메이트는 폴리(비닐 신나메이트)에 비해 빠른 반응속도를 나타내었다. 폴리(비닐 신나메이트)를 주성분으로 하여 올리고머 신나메이트를 블렌드한 경우 반응속도가 약간 향상되는 특성을 확인하였다. 올리고머 신나메이트는 높은 결정성으로 인해 표면 그루브 패턴을 단독으로 형성할 수 없었지만 폴리(비닐 신나메이트)와의 블렌드를 통하여 그루브 패턴을 형성할 수 있었으며 그루브 패턴에서도 polar plot에 의해 분자 배향성을 나타냄을 확인하였다. 올리고머 신나메이트와 고분자계 신나메이트의 블렌드를 통하여 반응속도의 향상과 박막 구조의 패턴을 형성하기에 적합함의 확인을 통해 새로운 광배향막 재료로 적용 가능함을 알 수 있었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.269-270
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• 2009

The biased vertical alignment (BVA) liquid crystal (LC) mode shows a has a distinct advantage of lower manufacture cost due to the elimination of a lithographic process step to form either ITO-patterning or protrusions on the color-filter substrates. However, those devices have complex voltage conditions which is the respective induce voltage on common electrode, pixel electrode and bias electrode when positive and negative frame. In order to overcome the complex voltage condition, the pretilt angles is controlled by photo polymerization of the UV-curable reactive mesogen (RM). According to our studies, voltages to the cell are critical to achieve an optimized surface-modified quality BVA (Q-BVA) mode which provides the well defined reorientation of the LCs with respect to an electric field.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2006년도 6th International Meeting on Information Display
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• pp.421-421
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• 2006

The light and energy-efficiency of classical liquid crystal displays is notoriously poor due to the use of absorption-based linear polarisers and colour filters. For instance, the light efficiency of PVAL polarisers is typically between 40 and 45 % and the colour filters have a typical efficiency below 35 % which results in a total light and energy-efficiency of the display below 10 %. In the past, a variety of polarizers were developed with an enhanced efficiency in generating linearly polarized light. Typically, these polarizers are based on the polarisationselective reflection, scattering or refraction of light i.e. one polarisation direction of light is directly transmitted to the LCD/viewer and the other polarization direction of light is depolarised and recycled which results in a typical efficiency for generating linearly polarized light of 70-85 %. Also, special colour filters have been proposed based on chiral-nematic reactive mesogens which increase the efficiency of generating colour. Despite the enormous progress in this field, a need persists for improved methods for generating polarized light and colour based on low cost optical components with a high efficiency. Here, the use of holographic phase gratings is reported for the generation of polarized light and colour. The phase grating are recorded in a photopolymer which is coated onto a backor frontlight for LCDs. Typically the recording is performed in the transmisson mode or in the waveguiding mode and slanted phase gratings are generated with their refractive index modulation at an angle between 20o and 45o with the normal of the substrate. It is shown that phase gratings with a high refractive index modulation and a high efficiency can be generated by a proper selection of the photopolymer and illumination conditions. These phase gratings coupleout linearly polarized light with a high contrast (> 100) and the light is directed directly to the LCD/viewer without the need for redirection foils. Dependent on the type of phase grating, the different colours are coupled-out at a slightly different angle which potentially increases the efficiency of classical colour filters. Moreover, the phase gratings are completely transparent in direct view which opens the possibility to use them in frontlights for LCDs. Holographic polarization gratings posses a periodic pattern in the polarization state of light (and not in the intensity of light). A periodic pattern in the polarization direction of linearly polarized light is obtained upon interference of two circularly polarized laser beams. In the second part of the lecture, it is shown that these periodic polarization patterns can be recorded in a linear photo-polymerizable polymer (LPP) and that such an alignment layer induces a period rotation in the director of (reactive and non-reactive) liquid crystals. By a proper design, optical components can be produced with only first order diffraction and with a very high efficiency (>0.98). It is shown that these diffraction gratings are potentially useful in projection displays with a high brightness and energy efficiency