• Macromolecular Research
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• 제14권2호
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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.

• 접착 및 계면
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• 제6권2호
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• pp.1-5
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• 2005

Single crystals of metallocene-catalyzed isotactic polypropylene (iPP) and/or syndiotactic PP (sPP) were prepared and preliminarily characterized. The crystallization was performed utilizing 0.1 % by weight concentrations of each PP in o-xylene in the range of temperature of $40{\sim}90^{\circ}C$. Following the XRD patterns, samples were ${\alpha}$-iPP and antichiral Cell III of sPP. The XRD pattern of iPP shows three ${\alpha}$-form peaks due to the (110), (040), (130) planes at $2{\theta}=14.2^{\circ}$, $17^{\circ}$, $18.8^{\circ}$, respectively. The XRD pattern of sPP is characterized by the presence of the (020) reflection at $16^{\circ}$. The melting point ($123^{\circ}C$ and $148^{\circ}C$, respectively) of the metallocene catalyzed iPP and sPP were generally lower than that of conventional PP ($160{\sim}170^{\circ}C$) due to the misinsertion of the monomer. When metallocene-catalyzed iPP samples were crystallized isothermally from solution grown at a lower temperature, lozenge shape single crystals were observed by transmission electron microscopy (TEM).

• Bulletin of the Korean Chemical Society
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• 제34권12호
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• pp.3903-3905
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• 2013

• Macromolecular Research
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• 제11권6호
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• pp.511-513
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• 2003

Hydroxyl groups were introduced onto the surface of a silicon wafer by O$_2$ plasma treatment. Poly(l-lactide) (1-PLA) was attached onto the surface-modified silicon wafer by the ring-opening polymerization of l-lactide using the hydroxyl group as an initiator. Lamellar single crystals of 1-PLA were grown directly on the 1-PLA-attached silicon wafer from a 0.025% solution in acetonitrile at 5$^{\circ}C$. A well-separated, lozenge-shaped, monolayered lamellar single crystal was prepared because the 1-PLA-attached silicon wafer acts as an initial nucleus.

• 폴리머
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• 제29권1호
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• pp.54-58
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• 2005

미생물 합성 poly[(R)3-hydroxybutyrate]](P(3HB))의 알칼리 및 효소 분해거동을 단결정과 Langmuir 단분자막을 모델시스템으로 하여 연구하였다. 단결정의 초기효소 및 알칼리 분해거동은 단결정의 장축에 대해 수직방향(b축)으로 분해가 일어났고 용융점 이하의 온도에서 열처리 또한 단결정의 b축을 따라 봉우리 형태의 형태학적 변화를 관찰하였다. 이러한 결과는 라멜라 단결정은 b축을 따라 불규칙한 영역을 가지고 있음을 의미하고 효소분해가 불규칙한 영역에서 선호적으로 일어난다고 설명할 수 있다. 한편, P(3HB), 단분자막의 효소 및 알칼리 분해경향은 분해매체와 표면압력에 크게 의존하였다. 알칼리 분해의 경우 낮은 표면압력에서도 분해를 나타내는 반면 효소 분해는 높은 표면 압력 하에서 분해거동을 나타내었다. 이러한 현상은 분자수준의 크기인 알칼리 분해매체는 P(3HB) 단분자막과 좁은 접촉면적(낮은 표면압력)에서도 활성을 보이는 반면 크기가 큰 분해효소는 보다 큰 활성 접촉면적(높은 표면압력)을 필요로 하는 것으로 판단된다.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2007년도 7th International Meeting on Information Display 제7권2호
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• pp.1125-1128
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• 2007

The laminating technique for developing flexible liquid crystal display was demonstrated by using a thin UV curable polymer film and a plastic substrate with patterned polymer wall structure. We adopted the rigid wall structure to provide a solid mechanical support for the stable molecular alignment of liquid crystals (LCs) in the device. The cover film was prepared to have an ability of aligning LC molecules by patterning a micro-groove structure using the soft-lithographic process. These two substrates can be assembled tightly by the laminating and one-step UV irradiation process because of the adhesive nature of the used UV curable polymers. Proposed method can be used to fabricate the flexible LC display with simplicity and also be applicable for a cost-effective roll-to-roll process.

• 한국고분자학회:학술대회논문집
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• 한국고분자학회 2006년도 IUPAC International Symposium on Advanced Polymers for Emerging Technologies
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• pp.65-66
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• 2006

[ $TiO_2$ ] single crystalline nanorods are prepared from electrospun fibers which are composed of nanofibrils with an island-in-a-sea morphology. The mechanical pressure produces each fibril into nanorods which are converted to anatase single crystals after calcinations. HRTEM shows that the (001) plane is growing along the longitudinal direction of the rod. In this work, the nanorod electrode provides the efficient photocurrent generation in a quasi-solid state dye-sensitized solar cells (DSSCs) using highly viscous PVDF-HFP based gel electrolytes. The overall converision efficiency of the $TiO_2$ nanorods shows 6.2 % under $100\;mW/cm^2$ (AM 1.5G) illumination.

• Transactions on Electrical and Electronic Materials
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• 제11권3호
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• pp.134-137
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• 2010

We have proposed a transflective liquid crystal display (LCD) driven by the fringe field using a liquid crystal (LC) with a negative dielectric anisotropy. The device used different twist angles of the liquid crystals (LC) in the transmissive (T) and the reflective (R) regions when voltage is applied. With the optimization of the pixel electrode width and the distance between them, the LC directors in the R- and T-regions can be rotated by about $22.5^{\circ}$ and $45^{\circ}$ on an average, respectively. As a result, a high image quality transflective LCD with a single gap, a single gamma, and a wide viewing angle characteristics in both the R- and T- regions can be realized.

• Macromolecular Research
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• 제12권2호
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• pp.189-194
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• 2004

When water is evaporated quickly from a water-based colloidal suspension, colloidal particles protrude from the water surface, distorting it and generating lateral capillary forces between the colloidal particles. The protruded colloidal particles are then assembled into ordered colloidal crystalline domains that float on the water surface on account of their having a lower effective density than water. These colloidal crystal domains then assemble together by lateral capillary force and convective flow; the generated colloidal crystal has grain boundaries. The single domain size of the colloidal crystal could be controlled, to some extent, by changing the rate of water evaporation, but it seems very difficult to fabricate a single crystal over a large area of the water's surface without reorienting each colloidal crystal domain. To reorient such colloidal crystal domains, a glass plate was dipped into the colloidal suspension at a tilted angle because the meniscus (airwaterglass plate interface) is pinned and thinned by further water evaporation. The thinning meniscus generated a shear force and reoriented the colloidal crystalline domains into a single domain.

• 한국전기전자재료학회논문지
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• 제13권1호
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• pp.52-59
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• 2000

In order to develop the transparent anti-static film with higher than 80% transparency to visible light, organic conductive compounds, N-methyl phenazinium 7,7,8,8-tetracyanoquinonedimethane (TCNQ) com-plex salts was synthesized and bar-coated on the polythylene terephthalate (PET) film using polymer binders. The best surface properties were obtained when acrylic binder was used. A single layer of TCNQ made of a acrylic binder showed a surface resistance of 10\ulcorner $\Omega$/ , a conductivity of 10\ulcorner S/cm, and a transparency of 75%. An optical microscopic examination revealed that the binder was first solidi-fied on the surface of PET film over which the needle-shaped TCNQ crystals were grown. An acrylic polyol coating over the TCNQ layer improved the transparency to 87%, becuase the acrylic polyol covers the surface of TCNQ crystals to reduce the surface roughness. This conductive material has thermal stability at room temperature and 4$0^{\circ}C$ over 4,000 h.