• Bulletin of the Korean Chemical Society
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• 제19권8호
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• pp.868-874
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• 1998

An equivalent retention has been experimentally observed in thermal field-flow fractionation (ThFFF) for different polymer-solvent systems. It is shown that iso-retention between two sets of polymer-solvent systems can be obtained by adjusting the temperature difference (ΔT) according to the difference in the ratio of ordinary diffusion coefficient to thermal diffusion coefficient. This method uses a compensation of field strength (ΔT) in ThFFF at a fixed condition of cold wall temperature. It is applied for the calculation of molecular weight of polymers based on a calibration run of different standards obtained at an adjusted AT. The polymer standards used in this study are polystyrene (PS), polymethylmethacrylate (PMMA), and polytetrahydrofuran (PTHF). Three carrier solvents, tetrahydrofuran (THF), methylethylketone (MEK) and ethylacetate (ETAc) were employed. Though the accuracy in the calculation of molecular weight is dependent on the difference in the slope of log λ vs. log M which is related to Mark-Houwink constant a, it shows reasonable agreement within about 6% of relative error in molecular weight calculation for the polymer-solvent systems having similar a value.

• 한국광학회:학술대회논문집
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• 한국광학회 2003년도 하계학술발표회
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• pp.14-15
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• 2003

Polymer optical fibers (POFs) are being considered as important high-speed communication media in the area of local area networks, datalinks and optical sensors. Large core diameter (500～1000 $\mu$m) and large numerical aperture (0.2~0.9) in a POF allow easy processing and connectorization, low cost high efficiency of beam coupling from LDs or LEDs, and complete immunity to EMI／EMR. There are many reports about 2.5 Gbps transmission the polymethylmethacrylate (PMMA) graded index (GI) POF over a distance of 100 m. (omitted)

• International Journal of Korean Welding Society
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• 제2권1호
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• pp.57-61
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• 2002

This paper presents development of a SEC(Solar Energy Concentration) utilizing the concentrated solar beam radiation for joining engineering thermoplastics such as Acrylonitrile/Butadiene/Styrene(ABS), Polycarbonate(PC) and Polymethylmethacrylate (PMMA). In addition, to study the joining of the materials, necessary experimentation with applying primer was performed. Tensile tests were conducted to determine the bond strength achieved at the specimen Joint interface. Microscopic examinations of the fractured joints were performed in order to analyze the overall bond quality. Finally, the results in terms of bond strength achieved at the joint interface and energy consumed in the process was compared with those obtained with similar thermoplastic joining technique utilizing microwave energy.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.91-91
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• 2010

본 논문은 펄스 직류전원 (Pulse DC) 플라즈마 소스와 반응성 가스인 $CF_4$와 불활성 가스인 Ar를 혼합하여 산업에서 널리 사용되는 유기고분자인 Polymethylmethacrylate (PMMA), Polyethylene terephthalate (PET), 그리고 Polycarbonate (PC) 샘플을 건식 식각한 결과에 대한 것이다. 각각의 샘플은 감광제 도포 후에 자외선을 조사하는 포토레지스트 방법으로 마스크를 만들었다. 펄스 직류전원 플라즈마 시스템을 사용하면 다양한 변수를 줄 수 있다는 장점이 있다. 공정 변수는 Pulse DC Voltage는 300 - 500 V, Pulse DC reverse time $0.5{\sim}2.0\;{\mu}s$, Pulse DC Frequency 100~250 kHz 이었다. 변수 각각의 값이 높아질수록 고분자의 식각률이 높아졌다. 특히, PMMA의 식각률이 가장 높았으며 PET, PC 순이었다. 샘플 중 PC의 식각률이 가장 낮은 이유는 고분자 결합 중에 이중결합의 벤젠 고리 모양을 포함하고 있어 분자 결합력이 비교적 높기 때문으로 사료된다. 기계적 펌프만을 사용한 공정 전 압력은 30 mTorr이었다. 쓰로틀 밸브를 완전 개방한 상태에서 식각 공정 중 진공 압력은 $CF_4$ 가스유량이 늘어날수록 증가하였다. 식각률 역시 $CF_4$ 가스유량(총 가스 유량은 10 sccm)이 많을수록 증가함을 보여주었다 (PMMA: 10 sccm $CF_4$에서 330 nm/min, 3.5 sccm $CF_4$/6.5 sccm Ar에서 260 nm/min., PET: 10 sccm $CF_4$에서 260 nm/min, 3.5 sccm $CF_4$/6.5 sccm Ar에서 210 nm., PC: 10 sccm $CF_4$에서 230 nm, 3.5 sccm $CF_4c$/6.5 sccm Ar에서 160 nm). 이는 펄스 직류전원 플라즈마 식각에서 $CF_4$와 Ar의 가스 혼합비를 조절함으로서 고분자 소재의 식각률을 적절히 변화시킬 수 있다는 것을 의미한다. 표면 거칠기는 실험 후 표면단차 측정기와 전자 현미경 등을 이용하여 식각한 샘플의 표면을 측정하여 알 수 있었다. 실험전 기준 샘플 표면 거칠기는 PMMA는 1.53nm, PET는 3.1nm, PC는 1.54nm 이었다. 식각된 샘플들의 표면 거칠기는 PMMA는 3.59~10.59 nm, PET은 5.13~11.32 nm, PC는 1.52~3.14 nm 범위였다. 광학 발광 분석기 (Optical emission spectroscopy)를 이용하여 식각 공정 중 플라즈마 발광특성을 분석한 결과, 탄소 원자 픽 (424.662 nm)과 아르곤 원자 픽 (751.465 nm, 763.510 nm)의 픽의 존재를 확인하였다. 이 때 탄소 픽은 $CF_4$ 가스에서 발생하였을 것으로 추측한다. 본 발표를 통해 펄스 직류전원 $CF_4$/Ar의 고분자 식각 결과에 대해 보고할 것이다.

• Journal of Korean Neurosurgical Society
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• 제29권3호
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• pp.365-371
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• 2000

Objectives : To describe a technique for percutaneous vertebroplasty of osteoporotic vertebral body compression fractures and to report preliminary results of its use. Methods : The technique was used over a 8-month period in 9 patients with 10 painful vertebral fractures. The technique involves percutaneous puncture of the involved vertebrae with a Jamshidi needle via a transpedicular approach followed by injection of polymethylmethacrylate(PMMA) into the vertebral body. Results : The procedure was technically successful in all patients, with an average injection amount of 5.9 cc per vertebral body. One patient complained of flank pain postoperatively in spite of improvement in back pain caused by the fractured vertebra. Remaining eight patients reported significant pain relief early after treatment. The patients were followed up for 3 to 15 months(average 7.2 months) and demonstrated no recurrence of pain or aggravation of deformity. Conclusion : Vertebroplasty appears to be a valuable tool in the treatment of painful osteoporotic vertebral fractures, providing acute pain relief and early mobilization in appropriate patients. However, it needs to have more extensive prospective clinical study to confirm its definitive role in the management of this condition.

• 접착 및 계면
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• 제20권1호
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• pp.23-28
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• 2019

본 연구에서는 마이크로 또는 나노 입자 형상을 폴리디메틸실록산 (PDMS)에 전사시켜 건식접착제를 제조하고 특성에 대하여 고찰하였다. 20 nm, 40 nm, 70 nm의 직경을 가지는 구리 나노 입자형상과 $5{\mu}m$의 직경을 가지는 폴리메틸메타아크릴레이트 (PMMA) 마이크로 입자 형상을 전사시켜 PDMS 건식 접착제를 제조하였다. 입자의 종류 및 크기가 변화함에 따라 건식 접착제의 기계적 특성, 인장 접착강도, 표면 형상, 접촉각, 광학적 성질에 미치는 영향을 조사하였다. 20 nm 직경을 가지는 구리 나노 입자를 전사시켜 얻은 건식 접착제는 bare PDMS 필름에 비하여 300% 이상 향상된 인장 접착강도를 가졌다. 나노 입자를 전사시켜 얻은 큰 표면적 건식 접착제 구조가 높은 인장 접착강도를 부여하는 원인으로 추정된다. 본 연구결과는 나노 입자를 전사시키는 방법이 PDMS 건식 접착제의 제조에 있어 쉽고 효과적임을 시사한다.

• 마이크로전자및패키징학회지
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• 제16권4호
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• pp.29-32
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• 2009

기공의 밀도가 높은 다공성 실리콘 산화물 박막이 GaAs 기판 상에 형성이 되었다. 다공성 실리콘 산화막을 형성하기 위해서 자기조립 형태로 배열하는 블록공중합체를 사용하였다. GaAs 기판 상에 화학기상증착 (CVD)을 이용하여 실리콘 산화막을 형성하였다. 폴리스티렌 (PS) 바탕에 벌집 형태로 배열된 폴리메틸메타아크릴레이트 (PMMA)가 주기적으로 배열되어 있는 나노패턴 박막을 형성하였고 PMMA를 아세트 산으로 제거하여 PS만 남아있는 나노크기의 마스크를 형성하였다. 형성된 PS 나노패턴의 지름은 15 nm, 박막의 두께는 40 nm 였으며 이를 건식 식각용 마스크로 사용하여 화학반응성식각 (RIE) 을 진행하였고 PS의 나노패턴이 산화막 기판상에 전사되도록 하였다. 식각 시간을 조절하여 산화막에 형성된 기공이 GaAs 표면까지 연결되도록 하였고 이는 불산으로 산화막을 제거하여 확인하였다. 식각시간은 90초에서 110초였으며 산화막 상에 나노패터닝된 기공이 형성되는 식각 시간은 90초에서 100초 사이였다. 형성된 나노 패터닝된 산화막 기공의 지름은 20~22 nm였고 식각 시간에 따라서 조절이 가능함을 확인할 수 있었다.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1997년도 추계학술대회
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• pp.245-248
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• 1997

Operative interventions for the management of osteonecrosis of the femoral head (ONFH) include core drilling, with or without vascularized fibular bone grafting. Nevertheless, their clinical results have not been consistently satisfactory. Recently, a new surgical procedure that incorporates cementation with polymethylmethacrylate (PMMA) after core drilling has been tried clinically. In this study, a biomechanical analysis using a finite element method(FEM) was undertaken to evaluate surgical methods and their underlying surgical parameter. Our finite element models included five types. They were (1) normal model (Type I), (2) necrotic model (Type II), (3) core decompressed model (Type III). (4) fibular bone grafted model (Type IV), and (5) cemented with PMMA model (Type V). The geometric dimensions of the femur were based on digitized CT-scan data of a normal person. Various physiological loading conditions and surgical penetration depths by the core were used as mechanical variables to study their biomechanical contributions in stress transfer within the femoral head region. In addition. the peak von Mises stress(PVMS) within the necrotic cancellous bone of the femoral head was obtained. The fibular bone grafted method and cementation method provided optimal stress transfer behaviors. Here. substantial increase in the low stress level was observed when the penetration depth was extended to 0mm and 5mm from the subchondral region. Moreover, significant decrease in PVMS due to surgery was observed in the fibular bone grafted method and the cementation method when the penetration depths were extended up to 0 and 5mm from the subchondral region. The drop in PVMS was greater during toe-off than during heel-strike (57% vs. 28% in Type IV and 49% vs. 22% in Type V). Both the vascularized fibular bone grafting method (Type IV) and the new PMMA technique (Type V) appear to be very effective in providing good stress transfer and reducing the peak Von-Mises stress within the necrotic region. Overall results show that fibular bone grafting and cementation methods are quite similar. In light of above results, the new cementation method appears to be a promising surgical alternative or the treatment of ONFH. The use of PMMA for the core can be less prone to surgical complication as opposed to preparation of fibular bone graft and can achieve more immediate fixation between the core and the surrounding region.

• 한국전기전자재료학회논문지
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• 제30권9호
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• pp.577-582
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• 2017

The white light of a hybrid LED is obtained by using red and green organic fluorescent layers made of polymethylmethacrylate (PMMA) films, which function as color down-conversion layers of blue light-emitting diodes. In this research, we studied the fluorescence properties of a red organic fluorophore, employing perylene bisimide derivatives applicable to hybrid LEDs. The solubility, thermal stability, and luminous efficiency are important characteristics of organic fluorophores for use in hybrid LEDs. The perylene fluorescent compounds (1A and 1B) were prepared by the reaction of 4-bromophenol and 4-iodophenol with N,N'-bis(4-bromo-2,6-diisopropylphenyl)-1, 6,7,12-tetrachloroperylene-3,4,9,10-tetracarboxyl diimide (1) in the presence of dimethyl formaldehyde (DMF) at $70^{\circ}C$. The synthesized derivatives were characterized by using $^1H-NMR$, FT-IR, UV/Vis absorption and PL spectra, and TGA analysis. Compounds 1A and 1B showed absorption and emission at 570 nm and 604 nm in the UV/Vis spectrum. We also documented favorable solubility and thermal stability characteristics of the perylene fluorophores in our work. Perylene fluorophore 1, with the 4-bromophenol substituent 1A, exhibited particularly good thermal stability and solubility in organic solvents.

• 한국재료학회지
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• 제20권6호
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• pp.331-337
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• 2010

A highly porous Biphasic Calcium Phosphate (BCP) scaffold was fabricated by the sponge replica method with a microwave sintering technique. The BCP scaffold had interconnected pores ranging from $80\;{\mu}m$ to $1000\;{\mu}m$, which were similar to natural cancellous bone. To enhance the mechanical properties of the porous scaffold, infiltration of polycaprolactone (PCL) was employed. The microstructure of the BCP scaffold was optimized using various volume percentages of polymethylmethacrylate (PMMA) for the infiltration process. PCL successfully infiltrated into the hollow space of the strut formed after the removal of the polymer sponge throughout the degassing and high pressure steps. The microstructure and material properties of the BCP scaffold (i.e., pore size, morphology of infiltrated and coated PCL, compressive strength, and porosity) were evaluated. When a 30 vol% of PMMA was used, the PCL-BCP scaffold showed the highest compressive strength. The compressive strength values of the BCP and PCL-BCP scaffolds were approximately 1.3 and 2MPa, respectively. After the PCL infiltration process, the porosity of the PCL-BCP scaffold decreased slightly to 86%, whereas that of the BCP scaffold was 86%. The number of pores in the $10\;{\mu}m$ to $20\;{\mu}m$ rage, which represent the pore channel inside of the strut, significantly decreased. The in-vitro study confirmed that the PCL-infiltrated BCP scaffold showed comparable cell viability without any cytotoxic behavior.