• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 추계학술대회 논문집 광주전남지부
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• pp.107-108
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• 2006

High $J_c$ $YBa_2Cu_3O_x$, superconducting films were fabricated by MOD method using fluorine-free dichloroacetic acid(DCA) as chelating solvent for preparing precursor solution. DCA-MOD precursor solution was coated on a single crystal (001) $LaAlO_3$(LAO) substrate by a dip coating method with a speed of 25 mm/min. Coated films were calcined at lower temperature up to $500^{\circ}C$ and Conversion heat treatment was performed at various temperatures of $780{\sim}810^{\circ}C$. SEM observations showed that films have very dense microstructures for the films prepared at the temperature higher than $800^{\circ}C$ regardless of diluting solvent; methanol or 2-methoxyethanol. A High critical current density ($J_c$) of 1.28 $MA/cm^2$ (@77 K and self-field) was obtained for the YBCO film prepared using 2-methoxyethanol as a solvent.

• 대한화학회지
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• 제42권1호
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• pp.84-91
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• 1998

고분자 전해질 복합체 형성이 poly(N-isopropyl acrylamide)(PNIPAAm) 공중합체의 저임계 용해온도 (lower critical solution temperature, LCST)에 미치는 영향을 조사하기 위하여 N-isopropyl acrylamide (NIPAAm)와 acrylic acid (AAc)를 선택하여 온도 감응성과 pH 감응성을 동시에 지니는 pH/온도감응성 고분자를 합성하였다.합성된 고분자들을 FT-IR과 적정실험을 통해 확인하였다. 고분자전해질로서 poly(allylamine) (PAA)과 poly(L-lysine)(PLL)을 사용하여 pH 2로부터 12에 이르는 넓은 범위의 pH 영역에서 고분자전해질 복합체 형성이 pH/온도감응성 고분자의 LCST에 미치는 영향을 조사하였다. 수용액상에서 poly(NIPAAm-co-AAc)중 PNIPAAm의 LCST는 cloud-point 측정 방법으로 결정하였다. 또한 역적정 실험을 통해 공중합체 중의 AAc 함량을 결정하고 AAc의 이온화 정도가 LCST에 미치는 영향을 조사하였다. 수용액상에서 poly(NIPAAm-co-AAc) 중 PNIPAAm의 LCST는 pH, 고분자전해질의 존재 유무, AAc의 함량, 그리고 고분자 사슬에 존재하는 전하밀도 등에 큰 영향을 받았다. 고분자전해질 복합체는 PAAc의 pKa와 PAA또는 PLL의 pKb 사이인 중성영역에서 형성됐으며 PNIPAAm의 LCST에 미치는 PLL의 영향은 PAA에 비해 크게 나타났다.

• 열처리공학회지
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• 제13권5호
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• pp.346-354
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• 2000

Effect of Nb addition on the phase transformation behavior was studied through continuous cooling transformation tests after reheating(reheating CCT) and deforming(deforming CCT) the 0.07%C-1.3%Mn-0.015%Ti-(0~0.08)% Nb steels. Transformation temperatures for deforming CCT were lower than those for reheating CCT, and the critical cooling rate for bainite transformation during deforming CCT was lower than that during reheating CCT. These enhanced hardenability for deforming CCT was considered to come from the sufficient solid solution of Nb in austenite during high temperature reheating before deformation. With Nb addition, the phase transformation temperature decreased, the bainite formation was enhanced, and the hardness of steel increased. Furthermore, these phenomena were more remarkable for deforming CCT than for reheating CCT. From the results, Nb-Ti bearing low carbon steel was considered to be a very favorable alloy system with good strength/toughness balance by recrystallization control rolling process.

• Bulletin of the Korean Chemical Society
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• 제34권6호
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• pp.1800-1808
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• 2013

Dual-responsive amphiphilic block copolymers were synthesized by combining enzymatic ring-opening polymerization (eROP) of ${\varepsilon}$-caprolactone (CL) and ATRP of N,N-dimethylamino-2-ethyl methacrylate (DMAEMA). The obtained block copolymers were characterized by gel permeation chromatography (GPC), $^1H$ NMR and FTIR-IR. The critical micelle concentration (CMC) of copolymer was determined by fluorescence spectra, it can be found that with hydrophilic block (PDMAEMA) increasing, CMC value of the polymer sample increased accordingly, and the CMC value was 0.012 mg/mL, 0.025 mg/mL and 0.037 mg/mL for $PCL_{50}$-b-$PDMAEMA_{68}$, $PCL_{50}$-b-$PDMAEMA_{89}$, $PCL_{50}$-b-$PDMAEMA_{112}$, $PCL_{50}$-b-$PDMAEMA_{89}$ was chosen as drug carrier to study in vitro release profile of anti-cancer drug (taxol). The temperature and pH dependence of the values of hydrodynamic diameter (Dh) of micelles, and self-assembly of the resulting block copolymers in water were evaluated by dynamic light scattering (DLS). The result showed that with the temperature increasing and pH decreasing, the Dh decreased. Drug-loaded nanoparticles were fabricated using paclitaxel as model. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) had been explored to study the morphology of the hollow micelles and the nanoparticles, revealing well-dispersed spheres with the average diameters both around 80 nm. In vitro release kinetics of paclitaxel from the nanoparticles was also investigated in different conditions (pH and temperature, etc.), revealing that the drug release was triggered by temperature changes upon the lower critical solution temperature (LCST) at pH 7.4, and at $37^{\circ}C$ by an increase of pH.

• 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.

• 청정기술
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• 제13권1호
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• pp.28-33
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• 2007

본 연구에서는 variable volume view cell이 장착된 상평형 장치를 사용하여 고압 상태의 다양한 용매 내에서 고분자인 Poly(methylmethacrylate) (PMMA)의 구름점(cloud point)를 측정하였다. 이때 사용된 용매는 chlorodifluoromethane (HCFC-22), dimethylether (DME), 1,1,1-trifluoroethane (HFC-143a), 1,1-difluoroethane (HFC-152a), 1,1,1,2-tetrafluoroethane (HFC-134a) 이였으며, 이들 용매에 $CO_2$를 첨가한 $HCFC-22+CO_2$와 $DME+CO_2$의 이성분계 혼합용매에서 $CO_2$의 조성 변화가 PMMA의 상거동에 미치는 영향을 살펴보았다. 실험 결과 PMMA는 HCFC-22에서는 340K, 5MPa 정도의 가장 낮은 온도 압력 조건에서부터 잘 용해되었으며 DME에서는 300K, 28MPa 정도의 비교적 낮은 온도 압력 범위에서 잘 용해되었으나, 그 밖의 불소화합물인 HFC-143a, HFC-152a, HFC-134a에서는 423.15K, 160MPa의 높은 온도 및 압력범위에서도 전혀 용해가 일어나지 않았다. 또한, PMMA+HCFC-22 혼합물에 $CO_2$를 첨가한 $PMMA+HCFC-22+CO_2$계의 경우는 LCST (lower critical solution temperature)의 상거동을 보였으나 PMMA+DME 혼합물에 $CO_2$를 첨가한 $PMMA+DME+CO_2$계의 경우는 UCST (upper critical solution temperature)의 상거동을 보였다. $CO_2$ 혼합용매 내에서 cloud point 압력은 동일한 온도에서 첨가되는 $CO_2$의 양에 비례하여 급격히 높아지는 것을 관찰할 수 있었고, 이로부터 PMMA를 SAS (supercritical antisolvent) 법에 의해 미세입자화 할 경우 $CO_2$가 DME와 HCFC-22에 대한 역용매로 사용될 수 있다는 것을 확인할 수 있었다. 또한 $CO_2$의 농도를 변화시킴으로써 PMMA의 cloud point를 자유롭게 조절할 수 있다는 것을 알 수 있었다.

• 한국재료학회지
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• 제21권11호
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• pp.617-622
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• 2011

The effect of oxygen on the shape memory characteristics in Ti-18Nb-6Zr-XO (X = 0-1.5 at%) biomedical alloys was investigated by tensile tests. The alloys were fabricated by an arc melting method at Ar atmosphere. The ingots were cold-rolled to 0.45 mm with a reduction up to 95% in thickness. After severe cold-rolling, the plate was solution-treated at 1173 K for 1.8 ks. The fracture stress of the solution-treated specimens increased from 450 Mpa to 880 MPa with an increasing oxygen content up to 1.5%. The fracture stress increased by 287MPa with 1 at% increase of oxygen content. The critical stress for slip increased from 430 MPa to 695 MPa with an increasing oxygen content up to 1.5 at%. The maximum recovery strain of 4.1% was obtained in the Ti-18Nb-6Zr-0.5O (at%) alloy. The martensitic transformation temperature decreased by 140 K with a 1.0 at% increase in O content, which is lower than that of Ti-22Nb-(0-2.0)O (at%) by 20 K. This may have been caused by the effect of the addition of Zr. This study confirmed that addition of oxygen to the Ti-Nb-Zr alloy increases the critical stress for slip due to solid solution hardening without being detrimental to the maximum recovery strain.

• Archives of Pharmacal Research
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• 제23권4호
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• pp.367-373
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• 2000

Cholic acid, conjugated with amine-terminated poly(W-isopropylacrylamide) (abbreviated as CA/ATPNIPAAm), was synthesized by a N, N'-dicyclohexyl carbodiimide (DCC)-mediated coupling reaction. Self-assembled CA/ATPNIPAAm micelles were prepared by a diafiltration method in aqueous media. The CA/ATPNIPAAm micelles exhibited a lower critical solution temperature (LCST) at $31.5^{\circ}C$. Micelle sizes measured by photon correlation spectroscopy (PCS) were approximately 31.6 $\times$$\times$ 5.8 nm. The CA/ATPNIPAAm micelles were spherical and their thermal size transition was observed by transmission electron microscope (TEM). A fluorescence probe technique was used for determining the micelle formation behavior of CA/ATPNIPAAm in aqueous solutions using Pyrene as a hydrophobic Probe. The critical micelle concentration (CMC) was evaluated as $8.9{\times}0^{-2}$ g/L. A drug release study was performed using indomethacin (IN) as a hydrophobic model drug. The release kinetics of IN from the CA/ATPNIPAAm micelles revealed a thermo-sensitivity by the unique character of poly(N-isopropylacrylamide) i.e. the release rate was higher at $25^{\circ}C$ than at $37^{\circ}C$.

• 대한화학회지
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• 제47권3호
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• pp.257-264
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• 2003

본 연구에서는 외부온열 온도$(~40^{\circ}C)$에서 항암약물(doxorubicin)이 방출되는 온도민감성 리포좀에 대하여 연구하였다. 온도민감성 리포좀은 외부온열온도에서 하한임계용액온도의 성질을 나타내는 N-isopropylacrylamide (NIP-AAm)와 Acrylamide(AAm)의 합성고분자에 의하여 변형되었다. 변형된 리포좀으로부터 약물(doxorubicin)의 방출은 온도와 시간의 변화에 따라서 형광강도를 측정하여 결정하였다. Poly(NIPAAm-co-AAm) copolymer에 의하여 변형된 리포좀으로부터 약물(doxorubicin)의 방출은 Poly(NIPAAm-co-AAm) copolymer가 온열온도 범위$(~40{\pm}2^{\circ}C)$에서 적절한 전이를 나타내기 때문에 증가하였다. 또한, 리포좀으로부터 약물의 방출은 5분 이내에 완료되었고, 변형된 리포좀의 크기는 120~170 nm 이었다. 본 연구에서는 온도에 의하여 제어 할 수 있는 온도민감성 리포좀을 제조하였다. 이것은 온도 제어에 따른 종양 표적화에 대한 약물전달시스템에서 활용 될 수 있을 것이다.

• 한국섬유공학회:학술대회논문집
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• 한국섬유공학회 2003년도 봄 학술발표회 논문집
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• pp.317-318
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• 2003

전기활성고분자인 poly(vinylidene fluoride)(이하 PVDF로 약기)와 전기비활성 고분자와의 혼화성블렌드에서 외부전장이 이 블렌드의 상분리거동에 미치는 영향을 조사하기에 적합한 전기비활성고분자를 찾은 결과 측쇄에 C=O기를 갖는 poly(ethyl methacrylate)(이하 PEMA)와 주쇄에 C=O기를 갖는 poly(1,4-butylene adipate)(이하 PBA로 약기)가 좋은 후보 고분자로 사용가능함을 보였다. 측쇄에 C=O기를 갖는 고분자인 PMMA와 PVDF와의 블렌드에서 PVDF의 융점보다 상당히 높은 온도인 35$0^{\circ}C$ 이상의 온도에서 lower critical solution temperature (이하 LCST로 약기) 거동을 보이는 것으로 알려져 있기 때문에 [1] 실제로 이들 블렌드계에서 열분해를 배제하면서 LSCT거동을 실험적으로 관찰하기는 불가능하다. (중략)