• Bulletin of the Korean Chemical Society
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• v.19 no.8
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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.

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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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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• v.2 no.1
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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.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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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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• v.29 no.3
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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.

• Journal of Adhesion and Interface
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• v.20 no.1
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• pp.23-28
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• 2019

In this study, the micro- and nano-particles were used and their shapes were transferred into the polydimethylsiloxane (PDMS) film to fabricate the dry adhesives and their properties were investigated. The Cu nanoparticles of the sizes of 20 nm, 40 nm and 70 nm and the polymethylmethacrylate (PMMA) beads of the size of $5{\mu}m$ were used to transfer their images and the resultant properties of the dry adhesives were compared. The effects of particle size and materials on the mechanical property, tensile adhesion strength, light transmittance, surface morphology, water contact angle were studied. The dry adhesives obtained from the transfer process of Cu nanoparticles with the size of 20 nm resulted in the enhancement of tensile adhesion strength more than 300% compared to that of the bare PDMS. The formation of nanostructure of large surface area on the surface of the PDMS film by the Cu nanoparticles may responsible for the improvement. This study suggests that the use of nanoparticles during the fabrication of PDMS dry adhesives is easy and effective and could be applied to the fabrication of the medical patch.

• Journal of the Microelectronics and Packaging Society
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• v.16 no.4
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• pp.29-32
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• 2009

Dense and periodic arrays of nano-sized holes were patterned in oxide thin film on GaAs substrate. To obtain the nano-size patterns, self-assembling diblock copolymer was used to produce thin film of uniformly distributed parallel cylinders of polymethylmethacrylate (PMMA) in polystyrene (PS) matrix. The PMMA cylinders were removed with UV expose and acetic acid rinse to produce PS nanotemplate. By reactive ion etching, pattern of the PS template was transferred to under laid silicon oxide layer. Transferred patterns were reached to the GaAs substrate by controlling the dry etching time. We confirmed the achievement of etching through the removing oxide layer and observation of GaAs substrate surface. Optimized etching time was 90 to 100 sec. Pore sizes of the nanopattern in the silicon oxide layer were 20~22 nm.

• Proceedings of the KOSOMBE Conference
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• v.1997 no.11
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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.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.9
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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.

• Korean Journal of Materials Research
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• v.20 no.6
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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.