• Journal of Powder Materials
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• v.6 no.4
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• pp.320-324
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• 1999

The formation, microstructure and properties of novel ceramic composite materials manufactured by active-filler-controlled polymer pyrolysis were investigated. In the presence of active filler particles such as transition metals, bulk components of various geometry could be fabricated from siliconorganic polymer. Molybdenum- and tungsten-filled polymer suspensions were prepared and their conversion to ceramic composites by annealing in $CH_4$ atmosphere were studied. Dimensional change. porosity and phase distribution (filler network) were analyzed and correlated to the resulting hardness values. Molybdenum and tungsten as active filler were carburized completely to $Mo_2C$, $W_2C$ and WC in $CH_4$ atmosphere. Consequently, microcrystalline composites with the filler reaction products embedded in a silicon oxycarbide glass matrix were formed. Hardness was increased with increasing carburization and reached 8.6-9.5 GPa in the specimen pyrolyzed in $CH_4$ atmosphere.

• Journal of the Korean Graphic Arts Communication Society
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• v.13 no.2
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• pp.19-32
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• 1995

Liquid crystal-polymer composite(LCPC) films are promising new materials for both projection displays and vision products. LCPC films consist of a continuous liquid crystal phase embedded in a three- dimensional network of polymer matrix. The liquid crystal in these LC phases can be electrically switched giving rise to an opaque scattering off-state and a transparent, non- scattering on-state. In this work, a premixture is composed of LC, UV-curable monomer and photonitiator. LCPC films are formed by photopolymerization induced phase separation from this premixture. In conclusion, structure and electro-optical properties of LCPC films strongly depends on the selection of monomer, LC content and curing rate.

• Journal of the Korean Graphic Arts Communication Society
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• v.14 no.1
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• pp.89-114
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• 1996

Liquid crystal-polymer composite(LCPC) films consisting of a continuous LC phase embedded in a three-dimensional network of polymer matrix are formed by photopolymerization-induced phase separ on. The LCPC films are switched from a light-scattering stats to a highly transparent stats on the application of electric fields. Since the alignment of LC molecular determines the electro-optical properties of films, the requirement for good contrast is to generate the nematic phase at high concentration. On the other hand, the concentration of UV-curable monomer must be increased above some critical value to from the flexible matrix of unbounded polymer. The mixing ratio of LC and UV-curable monomer affects the electro-optical and viscoelastic properties of LCPD films in two opposing ways. By controlling the phase separation process, at an LC fraction of 0.7, the maximum performance of LCPC films has been achieved, the response time of which is 2ms on the application of electric fields.

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.195-195
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• 2006

A superior electrophilic substitution reaction medium that is non-toxic, relatively less corrosive, and non-volatile electrophilic substitution reaction to afford high molecular weight linear and hyperbranched polyetherketones (PEK' s) was developed. The system has very strong driving force to give extra ordinary high molecular weight linear and hyperbranched PEK' s. The reaction medium was further extended to prepare various types of copolymers and covalently grafted polymers onto carbon nanotube (CNT) or carbon nanofiber (CNF). By using characteristic hydrophilic nature of the reaction medium, hyperbranched PEK' s could be synthesized from commercially available $A_3\;+\;B_2$ monomers without network formation via selective solubility of the monomers.

• Proceedings of the Membrane Society of Korea Conference
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• 1997.10a
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• pp.11-15
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• 1997

Liquid-liquid phase separation에는 nucleation and growth와 spinodal decomposition의 2가지 경로가 있다. 상온에서 고농도의 고분자 용액과 저량의 비용매의 조성의 근처에는 용해도 갭으로 들어가게 되면 비용매에 아주 미량의 고분자가 있는 조성을 갖는 핵이 고분자 용액 내에서 형성되고 이러한 핵은 여러게가 액적의 형태로 주위의 고분자 용액의 gelation에 의해서 성장이 멈출 때까지 커지게 된다. 여기서 어떤 고분자 상이 nucleation되는지가 매우 중요하게 된다. 실제 우리가 상전이 막을 제조할 경우는 대부분 10wt% 이상의 고분자 농도이므로 polymer-poor상이 nucleation이 된다. Spinodal decomposition의 경우는 용해도 갭을 빠르게 통과해서 nucleation이 일어나지 않고 spinodal line을 지나는 경우이다. 이러한 경우의 용액은 매우 불안정해서 약간의 농도 변화에도 자발적인 상분리가 일어나서 polymer-poor상과 polymer-rich상이 서로 얽혀져 있는 network구조를 형성하게 된다.

• Macromolecular Research
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• v.13 no.3
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• pp.194-205
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• 2005

The network structure of Ni-coated carbon black (NCB) composites filled with phenolic resin was investigated by means of using scanning electron microscopy, viscosity, interfacial tension, shrinkability, Flory-Huggins interaction parameters, and swelling index. The electrical properties of the composites have been characterized by measurement of the specific conductivity as a function of temperature. Additionally, the variation of conductivity with temperature for the composites has been reported and analyzed in terms of the dilution volume fraction, relative volume expansion, and barrier heights energy. The thermal stability of phenolic-NCB composites has been also studied by means of the voltage cycle processes. The experimental data of EMI wave shielding were analyzed and compared with theoretical calculations. The mechanical properties such as tensile strength, tensile modulus, hardness and elongation at break (EB) of NCB-phenolic resin composites were also investigated.

• Macromolecular Research
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• v.16 no.1
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• pp.45-50
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• 2008

This study examined the swelling behavior and in vitro release of a model drug, tetracycline-HCl, from alginate and alginate-polyaspartate (Alg-PASP) composite gel beads. The alginate and Alg-PASP composite beads were prepared using an ionic crosslinking method with aqueous $Ca^{2+}$. Their microporous morphology was observed by scanning electron microscopy. The swelling ratio of the beads in different media varied according to their composition, cross-linking density ($Ca^{2+}$ concentration), and pH of the aqueous medium. The in vitro release experiment of the tetracycline-HCl encapsulated beads in different media suggests that the release of the drug is governed mainly by the swelling properties of the polymer network. The presence of PASP was found to significantly influence the swelling properties and drug release profile.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.954-957
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• 2007

We analyzed conditions for fabricating zero-bias polymer-stabilized liquid crystal (PSLC) pi cells. A high curing voltage and a very low curing intensity are effective in fabricating the cell with a high bright state, a low dark state and therefore a steep T-V curve. However, the response time of the cell is slow. Finally, a dual-frequency PSLC pi cell with fast response time is developed. The obtained result reveals that the dual-frequency PSLC pi cell has a fast response of under 1ms.

• Bulletin of the Korean Chemical Society
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• v.6 no.3
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• pp.128-131
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• 1985

A series of copolymer membranes of 2-hydroxyethylmethacrylate (HEMA) with selected hydrophobic monomers were prepared without crosslinking agents. The equilibrium water content, the partition coefficient, and the permeability of the solutes such as urea, methylurea, 1,3-di-methylurea, and acetamide via these membranes were measured. The partition coefficient data show that as the hydrophobicity of solutes increased, the partition of solutes were dictated by hydrophobic interaction between solute and polymer matrix. Diffusion coefficients obtained in these experiments decrease as the water content of polymer membrane decreases. This decrease is blunt as the excess heat capacities, ${\phi}C^0_p$ (excess) in aqueous solution at infinite dilution of solute increases. To investigate the relationship between water content and diffusion coefficient, the results of the diffusion experiments were examined in light of a free-volume model of diffusive transport. The remarkable increase of urea mobility in the polymer network containing relatively larger bulk water can be considered as water structure breaking effect.

• Bulletin of the Korean Chemical Society
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• v.21 no.6
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• pp.557-561
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• 2000

Various enaryloxynitriles-terminated reactive polymer precursors containing rigid aromatic units were prepared from various diamines and 1-(p-formylphenyl)-1-phenyl-2,2-dicyanoethene (1). Arylate end-capped model compounds linked with azomethine bond were also prepared by reacting p-formylphenyl benzoate with diamines to compare the curing ability. The oligomers were highly soluble in polar aprotic solvents such as N,N-dimethylformamide, dimethylsulfoxide and N-methyl-2 -pyrrolidinone. They generally showed an exothermic curing process between $280-350^{\circ}C$, attributable to the thermal crosslinking of the dicyanovinyl group in DSC analysis, and no weight loss at curing temperature. Upon heating the polymer precursors, heat-resistant and insoluble network polymers were obtained. Thermogravimetric analyses of the precursors containing rigid aromatic units showed thermal stability with a 77-92% residual weight at $500^{\circ}C$ under nitrogen.