• Macromolecular Research
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• v.14 no.2
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• pp.155-165
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• 2006

The present article describes the experimental and theoretical observations on the formation of holographic, polymer-dispersed, liquid crystals and electrically switchable, photonic crystals. A phase diagram of the starting mixture of nematic liquid crystal and photo-reactive triacrylate monomer was established by means of differential scanning calorimetry (DSC) and cloud point measurement. Photolithographic patterns were imprinted on the starting mixture of LC/triacrylate via multi-beam interference. A similar study was extended to a dendrimer/photocurative mixture as well as to a single component system (tetra-acrylate). Theoretical modeling and numerical simulation were carried out based on the combination of Flory-Huggins free energy of mixing and Maier-Saupe free energy of nematic ordering. The combined free energy densities were incorporated into the time-dependent Ginzburg-Landau (Model C) equations coupled with the photopolymerization rate equation to elucidate the spatio-temporal structure growth. The 2-D photonic structures thus simulated were consistent with the experimental observations. Furthermore, 3-D simulation was performed to guide the fabrication of assorted photonic crystals under various beam-geometries. Electro-optical performance such as diffraction efficiency was evaluated during the pattern photopolymerization process and also as a function of driving voltage.

• Journal of the Optical Society of Korea
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• v.18 no.6
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• pp.753-761
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• 2014

We propose a two-step UV irradiation procedure to fabricate polymer-dispersed liquid crystal (PDLC) films by lamination. During the first UV treatment, before lamination, the UV-curable monomers coated on one film substrate are solidified through photo-polymerization as the phase separation between the liquid crystals and the monomers. Introducing an adhesion-enhancement layer on the other plastic substrate and controlling the UV irradiation conditions ensure that UV-induced cross-linkable functional groups remain on the surfaces of the photo-polymerized layers. Thereby, the adhesion stability between the top and bottom films is much improved during a second (post-lamination) UV treatment by further UV-induced cross-linking at the interface. Because the adhesion-enhancement and PDLC layers prepared by the bar-coating process are solidified before lamination, the PDLC droplet distribution and the cell gap between the two plastic substrates remain uniform under the lamination pressure. This ensures that the voltage-controlled light transmittance is uniform across the entire sample.

• Korean Journal of Optics and Photonics
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• v.17 no.1
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• pp.23-30
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• 2006

Effects of liquid-crystal droplets size on electro-optical properties of the polymer dispersed liquid crystals are investigated experimentally The liquid crystal droplets size was varied by controlling the Laser power for phase separation and LC/oligomer composition ratio. Electro-optical switching voltage is dependent on the LC/oligomer composition ratio and liquid crystal droplet size. The experimental results showed droplet size will be small and saturation voltage is increased but rise time will be short at high power illumination laser light for phase separation.

• KIEE International Transactions on Electrophysics and Applications
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• v.11C no.3
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• pp.75-80
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• 2001

Holographic polymer dispersed liquid crystals (HPDLCs) have fabricated by irradiating an Ar-ion laser ( ${\lambda}$=514nm) at various intensity on LC/acrylate monomer mixtures which were sandwitched between two ITO coated glass plates. Monomer systems were composed of dipentaerythritol-hydroxy penta acrylate (DPHPA, f=5)/monofunctional acrylate monofunctional monomers. The LC used in this system was E7 (BL001, Merck). Gratings were fabricated by periodic interference of twobeams. Reflection efficiency-irradiation intensity-monomer type relationships were obtained from the UV-visible spectra of the HPDLC films. Peaks were found at a bit smaller wavelength than 514nm, due to the shrinkage of mixture volume upon polymerization. Real time measurements of diffraction efficiency have been obtained according to monomer types and LC contents.

• Journal of the Korean Graphic Arts Communication Society
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• v.16 no.3
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• pp.15-27
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• 1998

Several aspects of polymer dispersed liquid crystal(PDLC) film properties make them interesting for display application. Most versions of PDLC materials are able to modulate light without the use of polarizers, which offers advantages in optical throughput(brightness) and viewing angle compared to polarizer-based display. In this papers, we attemped to doe minimum of remaining liquid crystals at polymer network for the liquid crystal-polymer composite (LCPC) films. In results, best phase separation behaviors turned out liquid crystal/monomer/oligomer mixture system.

• 한국정보디스플레이학회:학술대회논문집
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• 2003.07a
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• pp.263-265
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• 2003

Stressed liquid crystals, SLCs, consist of a lowdensity polymer network dispersed in a nematic host. We induced stress by shearing the material. Alignment layers are not required because the liquid crystal director uniformly aligns along the direction of shear. The shearing stress also eliminates light scattering and results in sub-millisecond switching speeds, making them good candidates for video display applications.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1394-1397
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• 2006

Polymer Dispersed Liquid Crystal (PDLC) films, of which the liquid crystal has negative dielectric anisotropy, were prepared from the phase separation between MJ001317 and a variety of compositions of resins by common polymerization induced phase separation method. In this work, the effects of resin compositions have been systematically investigated and it was found that the morphology and size of droplet, which is closely related to electro-optic properties, mainly depend on the rate of polymerization and cross-linking density for each resin composition. The reverse mode PDLC films from this newly developed formulation containing TPGDA/EHA/HMPPO showed the good off-state transmittance, contrast ratio (19/1), and relatively low driving voltage(10V).

• 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.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.11
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• pp.891-895
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• 2010

Polymer dispersed liquid crystal (PDLC) films were prepared by the phase separation method using the liquid crystal (E7) and prepolymers. This work investigated the electro-optical characteristics of various PDLC films. In order to have good contrast ratio, the polymer refractive index must be adjusted to the ordinary refractive index of the liquid crystal. The driving voltage of PDLC films were mainly affected by elastic deformation. E7-Ebecryl810-IOA-TMPTA-HMPPO system had good threshold voltage and driving voltage and E7-Ebecryl810-EHA-PEGDA-HMPPO system had good contrast ratio.

• 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.