• Fibers and Polymers
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• 제4권4호
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• pp.188-194
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• 2003

Phase behavior and spinodal phase separation kinetics in binary blends of a random copolymer of vinylidene fluoride and trifluoroethylene (75/25) [P(VDF/TrFE)] and poly(l,4-butylene adipate) (PBA) have been investigated by means of optical microscopic observation and time-resolved light scattering. The blends exhibited a typical lower critical solution temperature (LCST)∼${34}^{\circ}C$ above the melting temperature of the P(VDF/TrFE) crystals over the entire blend composition range. P(VDF/TrFE) and PBA were totally miscible in the temperature gap between the melting point of P(VDF/TrFE) and the LCST. Temperature jump experiments of the 3/7 P(VDF/TrFE)/PBA blend were carried out on a light-scattering apparatus from a single-phase melt state (${180}^{\circ}C$) to a two-phase region (205∼${215}^{\circ}C$). Since the late stage of spinodal decomposition (SD) is prevalent in the 3/7 blend, SD was analyzed using a power law scheme. Self-similarity was preserved well in the late stage of SD in the 3/7 blend.

• 한국전자통신학회논문지
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• 제4권2호
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• pp.130-135
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• 2009

제안된 구조는 polyphase decomposition과 look-up 테이블 방식을 이용하였다. Synopsys CAD tool을 이용한 모의실험을 통하여 제안한 방식이 기존 방식에 비해 54% 정도의 게이트 수를 감소시킬 수 있고, 9% 정도의 전력소모를 줄일 수 있음을 보인다.

• Journal of Pharmaceutical Investigation
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• 제35권2호
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• pp.95-99
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• 2005

Mucoadhesive microspheres were prepared by interpolymer complexation of chitosan with poly(acrylic acid) (PAA) and solvent evaporation method to increase gastric residence time. The chitosan-PAA complex formation was confirmed by differential scanning calorimetry and swelling study. The DSC thermogram of chitosan-PAA microspheres showed two exothermic peaks for the decomposition of chitosan and PAA. The swelling ratio of the chitosan-PAA microspheres was dependent on the pH of the medium. The swelling ratio was higher at pH 2.0 than at neutral pH. The results indicated that the microspheres were formed by electrostatic interaction between the carboxyl groups of PAA and the amine groups of chitosan. The effect of various process parameters on the formation and morphology of microspheres was investigated. The best microspheres were obtained when 1.5% of the high molecular weight chitosan and 0.3% of PAA were used as an internal phase. The optimum internal phase volume was 7%. The com oil was used as the external phase of emulsion, and span 80 was used as the surfactant. The prepared microspheres had spherical shape.

• Macromolecular Research
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• 제9권1호
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• pp.66-70
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• 2001

In this work, we present the development of phase structure of the poly(methyl methacrylate)(PMMA)/ poly(vinylacetate)(PVAc) mixtures in ethyl acetate solution by light scattering. The PMMA/PVAc blends cast from ethyl acetate solutions exhibited fine "modulated structures" over broad blend composition ranges, which originated from the spinodal decomposition of the ternary polymer solutions at low polymer concentrations during the casting. The periodic distance was depended on the blend compositions and evaporation times.

• 한국잠사곤충학회지
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• 제42권1호
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• pp.42-47
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• 2000

Structural and thermal characteristics of silk fibroin/poly(2-hydroxyethyl methacrylate)(PHEMA) blend films were investigated using FTIR, X-ray diffractometer, differential scanning calorimeter, thermogravimeter and scanning electron microscope. FTIR spectra showed that the conformation of silk fibroin prepared by dissolving in formic acid was $\beta$-sheet, which did not affected by blending with PHEMA. The X-ray diffraction patterns also showed that individual crystalline structure of silk fibroin and PHEMA was not affected for the blend films. The initial thermal decomposition temperature of silk fibroin/PHEMA blend film tends to be higher than either of silk fkbroin or PHEMA. Thermal stability of both polymers, more notably PHEMA, can be improved by blending two components. As a result of SEM observation, the phases separation for silk fibroin/PHEMA blend films occured regardless of blend ratio ; continuous and dispersed phase were silk fibroin and PHEMA component, respectively.

• Macromolecular Research
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• 제17권5호
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• pp.313-318
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• 2009

The side chain liquid crystal triblock copolymers (TBCs), which underwent phase transitions below their decomposition temperature, were prepared by copolymerization of poly(n-butyl acrylate) and a comonomer containing the mesogenic azobenzene group. The physical properties of TBCs in the distinctive transition temperature ranges were investigated in terms of the liquid crystal (LC) content in the copolymers. The phase transition temperatures traced optically, thermally and rheologically were well coincided one another and clearly exhibited the phase transition of smectic-nematic-isotropic with increasing temperature. In the smectic phase, increasing temperature made the liquid crystal system more elastic, but viscosity (${\eta}'$) remained almost constant. In the nematic phase, increasing temperature abruptly decreased ${\eta}'$ and G', ultimately leading to isotropic phase. Both smectic and nematic phases exhibited Bingham viscosity behavior but the former gave much greater yield stress at the same LC content.

• 한국막학회:학술대회논문집
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• 한국막학회 2004년도 Proceedings of the second conference of aseanian membrane society
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• pp.74-77
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• 2004

Porous membranes were prepared via thermally induced phase separation (TIPS) of (ethylene-co-vinyl alcohol) (EVOH)/glycerol mixtures. The liquid-liquid (L-L) phase boundaries are shifted to higher temperature when the ethylene contents in EVOH increase. Moreover, the kinetic study proved that the growth of droplets formed by the general liquid-liquid (L-L) phase separation obeyed a power-law scaling relationship in the later stage of spinodal decomposition (SD). A new phase separation mechanism was presented, in which the L-L phase separation could be resulted from the crystallization. The hollow fiber membranes were prepared. The membranes showed asymmetric structures with skin layer near the outer surface, the larger pores just below the skin layer and the smaller pores near the inner surface. The effect of ethylene content (EC) in EVOH, cooling water bath temperature and take-up speed on membrane performance was investigated.

• Macromolecular Research
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• 제16권8호
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• pp.725-733
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• 2008

Polyimide (PI) multilayer thin films were prepared by spin-coating from a poly(amic acid) (PAA) and poly(amic acid) ammonium salt (PAAS). PI was prepared from pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA) PAA. Different compositions of PAAS were prepared by incorporating triethylamine (TEA) into PMDA-ODA PAA in dimethylacetamide. PI multilayer thin films were spin-coated from PMDA-ODA PAA and PAAS. The PAAS comprising cationic and anionic moieties were spherical with a particle size of $20{\sim}40\;nm$. Some particles showed layers with ammonium salts, despite poor ordering. Too much salt obstructed the interaction between the polymer chains and caused phase separation. A small amount of salt did not affect the interactions of the interlayer structure but did interrupt the stacking between chains. Thermogravimetric analysis (TGA) showed that the average decomposition temperature of the thin films was $611^{\circ}C$. All the films showed almost single-step, thermal decomposition behavior. The nanostructure of the multilayer thin films was confirmed by X -ray reflectivity (XRR). The LF 43 film, which was prepared with a 4:3 molar ratio of PMDA and ODA, was comprised of uniformly spherical PAAS particles that influenced the nanostructure of the interlayer by increasing the interaction forces. This result was supported by the atomic force microscopy (AFM) data. It was concluded that the relationship between the uniformity of the PAAS particle shapes and the interaction between the layers affected the optical and thermal properties of PI layered films.

• Bulletin of the Korean Chemical Society
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• 제24권10호
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• pp.1485-1489
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• 2003

The gelation for di-(2-ethylhexyl) phthalate (DEHP)-plasticized poly(vinyl chloride) was studied by measuring time-resolved small-angle X-ray scattering (SAXS) and a flow of the solutions in test tube. It was found that for the gelation there were three regimes. At Regime I, the solution rapidly changed to a gel, and the SAXS intensity showed a peak and the peak intensity increased, keeping the peak angle constant. Applying the SAXS intensity to the kinetic analysis of the liquid-liquid phase separation, it was revealed that the spinodal decomposition proceeded to develop a periodic length of 29.9 nanometer in size, a hydrogen-bonding-type association in polymer rich phase followed, and then it induced fast gelation rate. At Regime II, the gelation slowly occurred and the SAXS intensity was not observed, suggesting that a homogeneous gel network was formed by a hydrogen-bonding. At regime III, the solution was a homogeneous sol.

• 멤브레인
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• 제12권2호
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• pp.97-106
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• 2002

Polysulfone (PSf/NMP/alcohol 용액과 chlorinated poly(vinyl chloride) (CPVC)/THF/Alcohol 용액에 대한 광산란 패턴을 SALS (Small angle light scattering)와 FE-SEM (field emission scanning electron microscope)을 이용하여 조사하였다. PSf 용액에서는 시간에 따라 q값의 최대 산란 강도를 보이는 광산란 거동을 나타내어 스피노달 (SD) 상분리 거동을 나타내는 반면, CPVC 용액에서는 q값이 증가함에 따라 광산란 강도가 줄어드는 핵성장 (NG) 거동을 나타냈다. 각 고분자 용액에서 상분리 중반과 후반부에서 비용매 첨가제로 사용된 알코올의 탄소수가 증가할수록 농도분극의 증가율은 줄어들었다. 또한, SD에서의 초반부의 시간에 따른 산란 강도는 비용매 첨가제의 종류에 무관하게 Cahn의 건형 이론에 잘 부합되었다. 또한, SALS 장치로 얻어진 기공크기와 전자현미경으로 얻어진 영역 크기는 상호간에 비교되었다. 20PSf/70NMP/10n-butano1 (w/w%) 용액에 대한 산란 패턴은 초기 상분리 거동에서부터 후기 거동까지 매우 선명하게 관측되었고, 초반, 중반, 그리고 후반부에 대한 SD에 대한 이론적 결과와 잘 일치하였다. 최고의 산란강도를 나타낸 각도의 크기는 n-butanol>n-propanol>methanol>no alcohol 순으로 관찰되었으며, 이 순서로 최종 형성된 막 단면의 기공 크기가 감소되는 것으로 조사되었다.