• Journal of Advanced Marine Engineering and Technology
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• v.33 no.7
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• pp.987-993
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• 2009

An experimental study is performed to investigate unsteady mixed convection in a horizontal channel with a heat source. Particle image velocimetry (PIV) with thermo-sensitive liquid crystal (TLC) tracers is used for visualization and analysis. This method allows simultaneous measurement of velocity and temperature fields at a given instant of time. Quantitative data of the temperature and velocity are obtained by applying the color-image processing to a visualized image, and neural network is applied to the color-to-temperature calibration. It is found that the periodic flow of mixed convection in a cavity appears at very low Reynolds numbers (Re<0.4), and the period decreases with increasing Reynolds numbers and increases with increasing aspect ratio.

• Journal of the Optical Society of Korea
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• v.18 no.4
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• pp.395-400
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• 2014

We proposed a method for fast turn-off switching of a vertically-aligned liquid crystal cell by low-temperature curing of the polymer structure. We confirmed that the turn-off times of the fabricated cells were reduced significantly as the curing temperature was lowered to $-20^{\circ}C$. We accounted for the effect of low-temperature curing on the turn-off time by using a mathematical model and by observing images obtained via scanning electron microscopy. We also confirmed that low-temperature curing is more effective in reducing the response time when the device is operated at a low temperature.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1600-1602
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• 1996

We have investigated the anisotropic dispersion force effects for surfaces alignment of liquid crystals (LCs) on rubbed polystyrene (PS) surfaces by unidirection. In microphotographs an of the textures, we obtained the nematic (N) LCs are shown to align in both direction parallel and perpendicular to the rubbing for region up to medium rubbing, however to align in the direction perpendicular to the rubbing for strong rubbing region. We suggest that the anisotropic dispersion force is very important rather than macro-surface groove effect to uniform alignment of LCs. We also measured the temperature dependence of extrapolation length of 5CB on rubbed PS surfaces for strong rubbing. It is shown that the polar anchoring strength of 5CB is very weak on rubbed PS surface compared to the rubbed polyimide (PI) surface.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.891-892
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• 2006

To test the correlation between grain shape and growth behavior we prepared WC-TiC-Co samples with rounded (Ti, W)C grains and faceted WC grains. The growth of rounded (Ti, W)C grains was normal. In contrast, the growth of faceted WC grains was abnormal or suppressed depending on the initial size of WC particles. These observations were explained using growth theories of crystals in a liquid and were also confirmed by a simulation using their growth equations. The present results thus demonstrate that the growth behavior of carbide grains in a liquid is governed only by their shape, irrespective of the presence of another phase.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.623-624
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• 2009

Here we report a photo polymerization-induced hybrid alignment of a nematic liquid crystal cell which can be applied for a roll to roll fabrication process. Predominant polymerization in the vicinity of UV incident front induced a diffusion of monomers toward front slide and anisotropic polymer network was formed parallel to the polarization direction of the UV light. This induced planar alignment of liquid crystals at the front slide. Simultaneously, homeotropic alignment was induced at the bottom slide as the polymers are phase-separated from a bottom slide.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.299-302
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• 2007

We propose a soft-lithographic patterning method for producing a multi-domain liquid crystal (LC) alignment. The LC alignment polyimide layers are periodically patterned in the pixel boundaries by a micromolding-in-capillaries method. In our structure, the initially homeotropic LC orientations in the pixel areas are changed to axially symmetric LC domains due to the symmetric pretilt of LC molecules on the pixel boundaries.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.493-495
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• 2007

Cinnamate groups are well-known for a dimerization reaction upon exposure to ultraviolet irradiation and a thermal reaction after being heated. In this study, to verify the thermal reaction of the cinnamate group in detail, we investigated the thermal crosslinking of cinnamate oligomers. The thermal reaction of cinnamate oligomers of low molecular weight is induced more readily by thermal energy compared with that of cinnamate polymers. The orientation of the liquid crystal depended on the length of the spacers in the cinnamate oligomers.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.10
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• pp.885-890
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• 1998

The electro-optical properties of polymer dispersed liquid crystals (PDLCs) depend on dispersion structures and nematic alignment which can be controlled by taking proper liquid crystal/polymer mixtures and process conditions. To achieve excellent electro-optical properties such as low driving voltage, good contrast ratio and negligible hysteresis, we have developed optimization procedure. Under the optimized conditions, PDLC of low threshold voltage less than 3.1 V, high contrast ratio more than 150 and negligible hysteresis were obtained.

• Proceedings of the Optical Society of Korea Conference
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• 2006.07a
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• pp.91-92
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• 2006

Liquid crystal (LC) alignment on $a-SiO_x$ thin film was investigated by means of X-ray photoemission spectroscopy and optical transmittance as we varied the deposition temperature and the target-to-substrate distance. LC molecules can be aligned vertically on $a-SiO_x$ film when the stoichiometric parameter x of $a-SiO_x$ is smaller than 1.56, but they can be aligned homogeneously when x is larger than 1.56. We also found that whether liquid crystals can be aligned vertically or homogeneously on $a-SiO_x$ film can be predicted simply by measuring the change in optical transmittance by deposition of $a-SiO_x$ thin film layers.

• KIEE International Transactions on Electrophysics and Applications
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• v.11C no.3
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• pp.91-95
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• 2001

Reflective holographic polymer dispersed liquid crystal(HPDLC) device has a multilayer structure consisting of alternate layers of polymer and liquid crystal droplets. Periodic modulation of a refractive index reflects light of a specific wavelength in accordance with Braggs law. Samples cured isotropically were illuminated with an Argon-ion lase at 514nm. We optimized the reflcetion efficiency of HPDLC as a function of monomer functionality, LC composition and irradiation intensity. The properties of the HPDLC films were observed by UV-visible spectroscopy. We found that the maximum reflection efficiency depends on the monomer functionality, LC composition, and laser intensity. We expect these films could be used in full-color reflective display by stacking them to obtain a mixture of colors.