• 한국정보디스플레이학회:학술대회논문집
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• 2005.07a
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• pp.181-186
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• 2005

We demonstrate that the finite rate of dielectric relaxation in liquid crystals which has been ignored previously causes profound effects in the fast dielectric reorientation of the director. The phenomenon is relevant for submillisecond switching of the director when the switching rate approaches the rate of dielectric relaxation through the reorientation of the molecular dipoles. A submillisecond switching ($15-400\;{\mu}s$ for an optical retardation shift $0.3-2.2\;{\mu}m$ in $10-15\;{\mu}m$ thick cells) is demonstrated for dual frequency nematic cells with high pretilt that maximizes the dielectric torque acting on the director. We propose the theory of dielectric response in which the electric displacement depends not only on the present (as in the standard theory) but also on the past values of electric field and director. We design an experiment in which the standard "instantaneous" model and our model predict effects of opposite signs; the experimental data support the latter model.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.1142-1146
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• 2004

The synthetic route and physical properties for three-ring derivatives, trans-2,3,2',3'-tetrafluoro-4-alkyl-4'-(4-alkyl-cyclohexyl)-biphenyl and 4-alkyl-cyclohexane carboxylic acid 2,3,2',3',4'-pentafluoro-biphenyl-4-yl ester are presented. They exhibit broad range nematic phases exceeding 30K and low viscosity of nematic liquid crystal mixtures containing these materials. Their viscosity is compared with that of homologues with a lateral isothiocyanate group and show large negative dielectric anisotropies. The threshold voltage $V_{th}$ was low enough to be operated at a driving voltage of 5V. Our novel LC compounds are suitable materials for the improvement of dielectric anisotropy of vertical align liquid crystal displays (VA-LDCs).

• Electrical & Electronic Materials
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• v.10 no.5
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• pp.461-466
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• 1997

In this paper, we developed the new non-rubbing liquid crystal (LC) alignment techniques in the cell with slanted non-polarized ultraviolet (UV) light irradiation on polyimide (PI) film. It is shown that the uniform alignment for nematic (N) LC is obtained by using slanted non-polarized UV light irradiation on PI surface. We successfully obtained that the pretilt angle of NLC is generated about 3.3 degree in the cell with slanted non-polarized UV light irradiation with 70 degree on PI surface, for the first time. It is considered that the pretilt angle generation in NLC is attributed to interaction between the LC molecular and the PI, which is broken the polymer by slanted non-polarized UV irradiation. Therefore, we concluded that the uniform LC alignment is attributed to anisotropic dispersion force due to photo depolymerization with slanted non-polarized UV light irradiation on PI surface.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.951-954
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• 2001

We investigated the aligning capabilities for nematic liquid crystal (NLC) using a in-situ photodimerization method on various photopolymer surfaces. High Pretilt angle of the NLC can be measured by obliquely polarized UV exposure of 30$^{\circ}$on a photo-crosslinkable polyimide (PI) based polymer surface for 3 min. The pretilt angle of the NLC generated on the photopolymer surface using the in-situ photodimerization method was higher than that of a blending photopolymers (PI and cinnamate materials).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.949-952
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• 2002

The mechanisms of pretilt angle generation for a nematic liquid crystal (NLC) with negative dielectric anisotropy on the blended polyimide (PI) surface containing trifluoromethyl moiety was studied. High LC pretilt angle on the blended polymer surface with F3 was measured and the pretilt angle increased with rubbing strength. However, the low LC pretilt angle on the blended polymer surface with F1 and F2 was measured. The high LC pretilt angle generated is attributable to trifluoromethyl moiety in backbone structure on the blended PI surface. Therefore, the high pretilt angle of NLC can be achieved by using the blended polymer surface.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.2
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• pp.130-132
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• 2001

The mechanisms of pretilt angle generation in nematic liquid crystal (NLC) with negative dielectric anisotropy on a rubbed polyimide (PI) surface for homeotropic alignment were studied. The pretilt angle of negative type NLC was smaller than that of the positive type NLC for all rubbing strength regions on the rubbed PI surface. The pretilt angle generated in NLC does not attributable to steric interaction between the fluorine moiety of NLC and the polymer surface on the rubbed PI surface. Consequently, the mechanism of the pretilt angle generation for homeotropic alignment is different from the one for homogeneous alignment.

• Transactions on Electrical and Electronic Materials
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• v.3 no.2
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• pp.1-5
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• 2002

Alignment effects for nematic liquid crystal (NLC) and electro-optical (EO) characteristics of the ion beam (IB) aligned twisted nematic (TN)-liquid crystal display (LCD) with oblique ion beam exposure on the diamond-like carbon (DLC) thin film surface were studied. A high pretilt angle of 3.5$^{\circ}$ in NLC by ion beam exposure on the DLC thin film layer can be measured. An excellent voltage-transmittance (V-T) curve of the ion beam aligned TN-LCD was observed with oblique ion beam exposure on the DLC thin film surface for 1 min. Also, a faster response time for the ion beam aligned TN-LCD with oblique ion beam exposure on the DLC thin film surface for 1 min can be achieved.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.11
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• pp.981-984
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• 2002

The mechanisms of pretilt angle generation for a nematic liquid crystal (NLC) with negative dielectric anisotropy on the blended polyimide (PI) surface containing trifluoromethyl moiety were studied. High LC pretilt angle on the blended polymer surface with F3 was measured and the pretilt angle increased with rubbing strength. However, the low LC pretilt angle on the blended polymer surface with F1 and F2 was measured. The high LC pretilt angle generated is attributable to trifluoromethyl moiety in backbone structure on the blended PI surface. Therefore, the high pretilt angle of NLC can be achieved by using the blended polymer surface.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.12
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• pp.1023-1026
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• 2001

The control of high pretilt angle for nematic liquid crystal (NLC) with negative dielectric anisotropy on the rubbed blending polyimide (PI) of homeotropic and homogeneous alignment surface was studied. High LC pretilt angle on the rubbing blending polyimide of homeotropic PI and SE-7492 surface was measured and the LC pretilt angle increased wish blending ratio and rubbing strength. However, the low LC pretilt angle on the rubbed blending polyimide of homeotropic PI and SE-150 surface was measured. The high pretilt angle of NLC can be achieved by using the blending PI surface.

• Electrical & Electronic Materials
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• v.10 no.9
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• pp.876-880
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• 1997

In this paper we investigated the transcription of liquid crystal (LC) alignment method by using memory effect of nematic(N) LCon polymide(PI) surface with side chain as for non-rubbing alignment techniques. That the monodomain alignment of aligned NLC is observed by microscope textures in the cells on PI surface with side chain. We obtained that the pretilt angle of NLC are generated about 3.7$^{\circ}$on PI surface. We suggest that the LC alignment by using transcription alingnment method is attributed to memory effect of NLC on PI surface.