• Polymer(Korea)
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• v.29 no.2
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• pp.183-189
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• 2005

Films of poly(vinyl alcohol)(PVA)/chitosan blends and its blend hydrogels were prepared by the solution casting method. The state of miscibility of the blends and blend hydrogels were examined over the entire composition range by differential scanning carorimetry (DSC), thermogravimetry (TGA), and dynamic mechanical analysis (DMA). DSC analysis shows the depression of melting point of PVA in the blends and the decrease of crystallization temperature of PVA in the blends were observed with increasing chitosan content in the blends. TGA analysis indicates that chitosan was thermally more stable than PVA and the thermal stability of PVA in the blends was higher than that of pure PVA, due to some interactions between two component polymers in the blend. The glass transition temperature $(T_g)$ of the chitosan and of PVA, measured by DMA, were at 160 and $90^{\circ}C$, respectively. The $T_g$ of the blends was changed with the content of chitosan in the blends. The results of thermal and viscoelastic analysis indicate some miscibility between component polymers in the blend exists. Moisture and cross linking in the blend and blend hydrogel, which strongly change thermal and physical properties of hydrophilic polymers, affected the miscibility of chitosan and PVA to a small extent.

• Journal of the Microelectronics and Packaging Society
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• v.23 no.1
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• pp.11-15
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• 2016

The organic light emitting diodes (OLEDs) have been studied as large flexible displays, light source and hard wares of internet of things. However, OLEDs show some drawbacks in terms of external environments due to the low work function of the metals and the reactive organic materials. In particular, the operation functions of the OLEDs tend to deteriorate rapidly by exposing the oxygen and moisture. So as to prevent it, domestic and overseas studies underway in various method such as ALD, PVD, CVD. But it has complex process and high cost. Therefore In order to protect devices from the external environments, it is important to develop the passivation thin films of low-cost and simple process which can prevent the devices from the penetration of the oxygen and moistures. In this study, to improve the reliability, passivation thin films were coated onto the green OLEDs by spin coating method and investigated the changes of the optical properties of the prepared devices at various doping concentrations of sodium alginate (SA). The passivation solutions were synthesized by using polyvinyl alcohol (PVA) host material with a dopant of SA which were added with the amounts of 10, 20 and 40 wt% into the PVA. As a result, the best barrier properties of the OLEDs were obtained for the samples with 40 wt% SA. Finally, the passivation films can be optimized by using the mixture solution of PVA and SA materials.

• Applied Chemistry for Engineering
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• v.24 no.2
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• pp.165-170
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• 2013

An external gelation method in place of an internal gelation method applied to the fabrication process of an intermediated compound of Uranium Oxy-Carbide (UCO) kernel spheres for Very High Temperature Reactor (VHTR) fuel preparation is under development in Korea. For the preliminary experiments of the UCO kernel sphere preparation using an external gelation method, the carbon black dispersion experiments were carried out using a simulated broth solution. From the selection experiments of various kinds of carbon black through dispersion experiments in a viscous metal salt solution, Cabot G carbon black was selected owing to its dispersion stability, and the homogeneous dispersing state of carbon black particles in our system. For the effective dispersion of nano-size aggregated carbon black particles in a high viscous liquid, the carbon black particles in a metal salt solution were first de-aggregated with ultrasonic force. The mixed solution was then dispersed secondly by the use of the extremely high-speed agitation with a mechanical mixer of 6000 rpm after feeding the Poly Vinyl Alcohol (PVA) in the solution. This results in the broth solution with good stability and homogeneity alongside no further changes in physical properties.

• Polymer(Korea)
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• v.27 no.6
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• pp.542-548
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• 2003

Nanoparticles with unsaturated poly(hydroxyalkanoate)s (UPHAs) biosynthesized with Pseudo-monas oleovorans were prepared by spontaneous emulsification solvent diffusion method. The influence of nanoparticle formation was investigated with various experimental parameters such as sonication conditions, sol-vent, surfactant and polymer contents, etc. The physical and chemical properties of UPHAS and its nanoparticles were characterized using $^1$H- and $\^$13/C-nuclear magnetic resonance spectroscopies, attenuated total reflection infrared spectroscopy, differential scanning calorimetry and gel permeation chromatography. The morphology of particles was observed using scanning electron microscope and the size and distribution of nanoparticles were measured with electrophoretic light scattering spectrophotometer. The mean diameter of particles decreased with increasing sonication amplitude and time. The addition of ethanol into UPHAS chloroform solution decreased the particle size presumably due to increased solvent diffusion into water phase. The particle size increased with increased the concentration of UPHAS solution. Under the 2-4％ poly(vinyl alcohol) (PVA) aqueous solution the minimum mean diameter of particles was shown. The higher degree of hydrolysis and degree of polymerization of PVA increased the mean diameter of particles.

• Membrane Journal
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• v.22 no.3
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• pp.208-215
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• 2012

Gel polymer electrolyte membranes were prepared from blends of polyvinyl alcohol (PVA) and poly (acrylic acid) (PAA), by solution-cast technique. The PAA content in the blend varied from 30 to 80 wt%. With the gel polymer electrolyte membranes, Zn air batteries were fabricated. The gel polymer electrolyte membranes were characterized by means of stress-strain test, impedance test. The Zn air batteries were tested by current interrupt method and galvanostatic discharge method. The tensile strength and tensile modulus decreased with increasing PAA content in the gel polymer electrolyte membrane. On the other hand, the ionic conductivity increased with increasing PAA content. The effect of ionic conductivity trend of the gel polymer electrolyte membrane in the Zn air battery was confirmed through current interrupt method and galvanostatic discharge method experiments. The battery with higher PAA content gel polymer electrolyte membrane showed lower IR drop and higher discharge capacity.

• Journal of Biomedical Engineering Research
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• v.43 no.4
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• pp.251-258
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• 2022

Silk fibroin microparticles were fabricated using a phase separation technique between silk fibroin solution and polyvinyl alcohol. We found that the concentration of polyvinyl alcohol determines the size of microparticles. The mean diameter of the silk fibroin microparticles varied from 3.48 ㎛ to 4.05 ㎛. The silk fibroin microparticle size increased as a function of the concentration of PVA in aqueous silk solution. The resulting silk fibroin microparticles have narrow size distribution (i.e. monodisperse) and smooth/spherical surface. Also, we studied the effects of mouse serum, sodium phosphate buffer (PBS), and pH on the stability of the silk fibroin microparticles. Overall, we demonstrated the simple method to fabricate and to control the silk fibroin microparticles that makes our silk microparticles to be usable for a potential drug delivery carrier.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1210-1213
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• 2006

The effect of surface treatment on CNT cathodes used in field emission displays was investigated. A liquid method using a polymer-based organic solution and a mechanical method were applied. The liquid method, using PVA(polyvinyl alcohol) showed high potential compared to the mechanical adhesive taping and rolling method used in the fabrication of CNT cathodes for large-sized field emission displays with high emission uniformity and a low cost.

• Journal of the Korean Ceramic Society
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• v.36 no.2
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• pp.186-192
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• 1999

Dang-Chin feldspar powder with the mean particle size of 9.1 $\mu\textrm{m}$ was added to the synthesized mullite powder with the particle size of +325∼-200 mesh and the powder compact was prepared by PLPP(pressureless powder packing method). Densification behaviors were observed in sintering temperature range of 1200∼1400$^{\circ}C$. The binder solution of 4% PVA was infilterated into packed powder to the suitable strength. The PLPP method makes it possible to form compacts without clay as plasticizer. Therfore there was no defect caused by phase transition after sintering. Additionally, we observed the dense microstructure by the melting of feldspar. When the mullite compacts with feldspar of 30% were sintered at 1300$^{\circ}C$-4 hrs, we obtained the dense microstructure with zero water absorption and porosity <1%. When these compacts were sintered longer than 4 hrs at 1300$^{\circ}C$ or higher than 1400$^{\circ}C$, the examggerated grain growth of mullite was observed.

• Journal of the Korean Ceramic Society
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• v.42 no.11 s.282
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• pp.729-736
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• 2005

HTGR (High Temperature Gas-cooled Reactor) is spotlighted to next generation nuclear power plant for producing the clean hydrogen gas and the electricity. In this study, the spherical $UO_3$ gel particles were prepared by the external gelation process, and the characteristics of these particles were analyzed the particle shape, composition of precipitate, and thermal decomposition characteristics with the Streoscope, FT-IR, and X-ray diffractometer. Raw material of the ADUN (Acid Deficient Uranyl Nitrate) solution, which has [$NO_3$]/[U] mole ratio = 1.75, was obtained from dissolution of the $U_{3}O_{8}$ powder with concentrated $HNO_3$, and its concentration is 3.5 M-U/l. The broth solution is prepared with the ADUN, urea, PVA, and THFA solution. The droplets of the broth solution was made through a nozzle system. From this study, we obtained the following results; 1) an externel chemical gelation process is a suitable method in the spherical $UO_3$ particle production, 2) the particle shape are changed by an urea mixing time, THFA volume, and the viscosity of the broth solution, 3) the amorphous $UO_3$ particles obtained from these experiments was converted to $U_{3}O_{8}$ and then $UO_2$ by heat treatment in hydrogen atmosphere at $600^{\circ}C$.

• Journal of Chest Surgery
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• v.36 no.2
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• pp.63-72
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• 2003

Although a variety of synthetic vascular grafts are available in modern vascular surgery, no ideal prosthesis ha,4 yet been developed. Small-caliber vascular grafts with low flow, as used in the lower extremity, continue to become thrombosed at unacceptable rates. We have developed and evaluated the new antithrombogenic blood contacting surfaces in canine model. Material and Method: Two now antithrombogenic blood contacting surfaces(Polyvinylalcohol -Polyurethane(PVA-PU) blend and natural Graphite-polyurethane(G-PU) blend) have been developed and evaluated in canine model, using vascular grafts and patches. The luminal surfaces of the test vascular grafts(5 mm ID) were fabricated by dipping a glass rod in PVA-PU blend solution(50 % PVA) using phase separation method. Mongrel dogs of either sex weighing 18-22 kg were anesthetized by endotracheal intubation using halothane and their lungs were ventilated with a volume-cycled ventilator, Maintenance anesthesia with 0.5-1.0% halothane and supplemental oxygen was used. Two pairs were used for comparison in the bilateral femoral arteries for both vascular grafts(PVA-PU vs. PU) and vascular patches(G-PU vs. PU). Bilateral groin incisions were made and the arteries were exposed and clamped. After an excision of 1 cm of the artery between clamps, a grail of 2.5 cm in length was implanted end-to-end using 6-0 polypropylene suture. The vascular patch was implanted as a form of on-lay patch. Animals were sacrificed at 1, 2, 4, 6, 8 and 16 weeks for vascular grafts and 1, 2. 4 and 6 weeks for vascular patches. Result The vascular grafts of PVA-PU blends showed patent lumina in the 2 and 16 weeks animals, while those of PU showed a patent lumen in 2 weeks animal. PVA-PU graft of 16 weeks showed a fairly clean luminal surface. A light microscopic finding of this graft demonstrated good tissue infiltration through porosity, The animals with vascular patches showed patent arteries in both groups except 2 weeks animal. Scanning electron microscopy of the luminal surfaces of G-PU patches in 4 and 6 weeks animals showed endothelial cell covering with microvilli. PU patches showed qualitatively less endothelial cell covering. Conclusion: In conclusion, PVA-PU and G-PU blends can be a promising blood contacting surfaces for application in a synthetic vascualr graft. However, further animal study is needed to determine the real long-term effects of these methods of surface modifications.