• 공업화학
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• 제25권2호
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• pp.181-187
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• 2014

구형의 아토마이징 제강 환원슬래그(래들로 슬래그)를 폴리머 콘크리트 복합재료의 잔골재 대신 사용하기 위하여 아토마이징 제강 환원슬래그의 대체율과 폴리머 결합재의 첨가율을 다양하게 변화시켜 공시체를 제작하였다. 공시체의제 물성을 조사하기 위하여 흡수시험, 압축 및 휨강도, 내열수성시험, 세공분포측정 및 SEM에 의한 미세조직 관찰을 실시하였다. 그 결과 폴리머 결합재 7.5% 첨가한 공시체는 제강 환원슬래그의 대체율이 증가됨에 따라 압축 및 휨강도가 증가되었으나 폴리머 결합재 8.0% 이상에서는 유동성의 증가로 인한 재료분리 현상으로 특정한 대체율에서 최대값을 나타내었다. 내열수성시험에 의하여 압축강도, 휨강도, 세공의 평균직경 및 밀도는 감소되었으나 총세공량과 공극률은 증가되었다. 아토마이징 제강 환원슬래그를 잔골재 대신 사용함으로써 유동성이 현저히 증가되어 폴리머 결합재의 사용량을 최대 23.5%까지 절감할 수 있는 것으로 나타났다. 그러나 아토마이징 제강 환원슬래그를 사용함으로써 내열수성이 감소되기 때문에 더 많은 연구가 요구된다.

• 대한의용생체공학회:의공학회지
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• 제44권6호
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• pp.404-413
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• 2023

In this research, we studied the development of a SUS304 microneedle array based on microfabrication technology and the applicability of Parylene-C thin film, a medical polymer material. First of all, four materials commonly used in the field of medical engineering (SUS304, Ti, PMMA, and PEEK) were selected and a 5 ㎛ Parylene-C thin film was deposited. The applicability of Parylene-C coating to each material was confirmed through SEM analysis, contact angle measurement, surface roughness(Ra) measurement, and adhesion test according to ASTM standards for each specimen. Parylene-C thin film was deposited based on chemical vapor deposition (CVD), and a 5 ㎛ Parylene-C deposition process was established through trial and error. Through characteristic experiments to confirm the applicability of Parylene-C, SUS304 material, which is the easiest to apply Parylene-C coating without pretreatment was selected to develop a microneedle array based on CNC micromachining technology. The CNC micromachining process was divided into a total of 5 steps, and a microneedle array consisting of 19 needles with an inner diameter of 200 ㎛, an outer diameter of 400 ㎛, and a height of 1.4 mm was designed and manufactured. Finally, a 5 ㎛ Parylene-C coated microneedle array was developed, which presented future research directions in the field of microneedle-based drug delivery systems.

• Journal of Korean Neurosurgical Society
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• 제30권11호
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• pp.1271-1277
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• 2001

Objectives : Since vertebroplasty has been introduced, we performed short segment pedicle screw fixation with augmented intra-operative vertebroplasty in patients with unstable thoraco-lumbar fracture. Our intentions are to demonstrate the efficacy and indication of this new technique compare to conventional methods. Material and Methods : The surgery comprised of pedicle screw fixations on one level above and below the fracture site, and the fractured level itself, if pedicle is intact, and intra-operative vertebroplasty under the fluoroscopic guide with in-situ postero-lateral bone graft. Also, in cases of bone apposition, we removed those with small impactor through a transfascetal route. During the last 2 years, we performed in seven(7) unstable thoraco-lumbar fracture patients who consisted of two different characteristics, those four(4) with primary or secondary osteoporosis and three(3) of young and very healthy. All patients were followed clinically by A.S.I.A. score and radiography. Results : Mean follow up period was 14 months. We observed well decompressed state via transfascetal route in cases of bone fragments apposition and no hardware pullout in osteoporotic cases, no poly-methyl-methacrylate (PMMA) leakage through the fracture sites into the spinal canal, and no kyphotic deformities in both cases during follow-up periods. All patients demonstrated solid bony fusion except one following osteoporotic compression fracture on other sites. Conclusions : In the management of unstable thoraco-lumbar fracture, we believe that this short segment pedicle screw fixation with augmented intra-operative vertebroplasty reduce the total length or levels of pedicle screw fixation without post-operative kyphotic deformity.

• Bulletin of the Korean Chemical Society
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• 제35권11호
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• pp.3199-3204
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• 2014

Two novel phosphorescent heteroleptic cationic Ir(III) complexes, Ir(bt)2(dmpe) (Ir1) and Ir (bt)2(dppe) (Ir2), where bt is 2-phenylbenzothiazole, dmpe is 1,2-bis(dimethylphosphino)ethane, and dppe is 1,2-bis(diphenyl-phosphino) ethane, were designed and synthesized. Their photophysical and electrochemical properties and the X-ray structure of the Ir1 complex were investigated. The prepared Ir(III) complexes exhibited blue-green emissions at 503-538 nm with vibronic fine structures in dichloromethane solution and PMMA film, implying that the lowest excited states are dominated by ligand-based $^3{\pi}-{\pi}^*$ transitions. The ${\pi}$-acceptor ability of the diphosphine ancillary ligand leads to blue-shift emission. The room temperature photoluminescent quantum yields (PLQYs) of Ir1 and Ir2 were 52% and 45%, respectively, in dichloromethane solution. These high PLQYs resulted from steric hindrances by the bulky cationic iridium complexes. The crystal structure of Ir1 was determined by X-ray crystallography, which revealed that central iridium adopted a distorted octahedral structure coordinated with two bt ligands (N^C) and one dmpe ligand (P^P) showing cis C-C and trans N-N dispositions. The bent nature of the dmpe ligand resulted in a relatively wide bite angle of $83.83^{\circ}$ of P-Ir-P.

• Tribology and Lubricants
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• 제24권2호
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• pp.63-71
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• 2008

Friction and adhesion tests were conducted to investigate tribological characteristics of materials for MEMS/NEMS using atomic force microscope (AFM). AFM Si tips were chemically modified with a self-assembled monolayer (SAM) derived from trichlorosilane like octadecyltrichlorosilane (OTS) and (1H, 1H, 2H, 2H-perfluorooctyl) trichlorosilane (FOTS), and various materials, such as Si, Al, Au, Cu, Ti and PMMA films, were prepared for the tests. SAMs were coated on Si wafer by dipping method prior to AFM tip to determine a proper dipping time. The proper dipping time was determined from the measurements of contact angle, surface energy and thickness of the SAMs. AFM tips were then coated with SAMs by using the same coating condition. Friction and adhesion forces between the AFM Si tip modified with SAM and MEMS/NEMS materials were measured. These forces were compared to those when AFM tip was uncoated. According to the results, after coating OTS and FOTS, the friction and adhesion forces on all materials used in the tests decreased; however, the effect of SAM on the reduction of friction and adhesion forces could be changed according to counterpart materials. OTS was the most effective to reduce the friction and adhesion forces when counterpart material was Cu film. In case of FOTS, friction and adhesion forces decreased the most effectively on Au films.

• Tribology and Lubricants
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• 제34권2호
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• pp.60-66
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• 2018

Graphene is a monolayer of carbon atoms (approximately 0.34 nm), arranged in a honeycomb network. It has been hailed as a next-generation flexible and transparent material because it has high electrical and thermal conductivities, excellent mechanical properties, as well as flexible and transparent properties. The wettability of graphene alters its adhesion or surface energy, and it is therefore an important parameter influencing its application in the fabrication of next-generation flexible and transparent electronics. Studies on the wettability of graphene are numerous and various opinions exist. However, almost all of these studies use the wet transfer method to transfer the graphene. In this study, therefore, we investigated the effect of wet and dry transfer methods on water contact angles of graphene on a substrate. The contact angles of substrates vary depending on the type of substrate. It was found that after graphene is transferred to the substrate, regardless of transfer method, the graphene/substrate contact angle increases to a value. The contact angle of graphene transferred using the dry transfer method is higher than the contact angle of graphene transferred using wet transfer methods. The wet transferred graphene is affected by the poly(methyl methacrylate) (PMMA) residue and the polar surface of substrate. The dry transferred graphene is influenced by the conformal contact between graphene and substrate.

• Journal of Advanced Marine Engineering and Technology
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• 제33권6호
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• pp.843-851
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• 2009

Much work has already been done to control and regulate the worldwide problems caused by climate change, particularly the issues on greenhouse gas (GHG) emissions. Carbon dioxide ($CO_2$), having the highest form of concentration among GHGs composed around 1.0 billion tons of emission, and comprises about 98% of the total emissions from the shipping industry. Korean trade mainly rely on the sea transportation. Korean ship tonnages that was brought about by shipbuilders all over the country, continues to grow annually due to the prevailing demands on goods or material supplies and depicting only a small part of the global maritime activity. Nowadays, new build ships coming from the Korean Shipbuilders are being optimized by hull, structure and appendages design, The operational capability of the propulsion and auxiliary machineries in its maximum capacity to achieve the highest possible efficiencies for energy and onboard power use to mitigate $CO_2$ emissions are continually being done through the help of research and development. In this paper, the energy efficiency design index and anboard power capacity of Korean new build ships have been analyzed with response to data collected by ship types, and its respective fuel consumption in relation to $CO_2$ emission results. In response to climate change convention outcome proposals, the best way for the new build ships to become energy efficient is by lowering its operational speed thru adopting the state of the art diesel propulsion engines, patronizing the best sailing practice to lower the transportation cost on the different sea trade routes also helps in $CO_2$ mitigation.

• Tribology and Lubricants
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• 제24권5호
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• pp.255-263
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• 2008

Adhesion tests were conducted to investigate the adhesion characteristics between mold and thermoplastic polymer film. Coating of anti-sticking layer (ASL), a kind of polymer material, imprint pressure, and separation velocity were considered as the process conditions. A piece of fused silica without patterns on its surface was used as a mold and the thermoplastic polymer films were made on Si substrate by spin-coating the commercial polymer solution such as mr-I PMMA and mr-I 7020. The ASL was derived from (1H, 1H, 2H, 2H - perfluorooctyl) trichlorosilane($F_{13}$-OTS) and coated on the fused silica mold in vapor phase. The pull-off force was measured in various process conditions and the surfaces of the mold and the polymer film were observed after separation. It was found that the adhesion characteristics between the mold and the thermoplastic polymer film and the release performance of ASL were changed according to the process conditions. The ASL was effective to reduce the pull-off force and the damage of polymer film. In cases of the mold coated with ASL, the pull-off force did not depend on imprint pressure and separation velocity.

• Geomechanics and Engineering
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• 제14권2호
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• pp.195-202
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• 2018

Many laboratory experiments on crack propagation under uniaxial loading and biaxial loading have been conducted in the past using transparent materials such as resin, polymethyl methacrylate (PMMA), etc. However, propagation behaviors of three-dimensional (3D) cracks in rock or rock-like materials under tri-axial loading are often considerably different. In this study, a series of true tri-axial loading tests on the rock-like material with two semi-ellipse pre-existing cracks were performed in laboratory to investigate the acoustic emission (AE) characteristics and propagation characteristics of 3D crack groups influenced by intermediate principal stress. Compared with previous experiments under uniaxial loading and biaxial loading, the tests under true tri-axial loading showed that shear cracks, anti-wing cracks and secondary cracks were the main failure mechanisms, and the initiation and propagation of tensile cracks were limited. Shear cracks propagated in the direction parallel to pre-existing crack plane. With the increase of intermediate principal stress, the critical stress of crack initiation increased gradually, and secondary shear cracks may no longer coalesce in the rock bridge. Crack aperture decreased with the increase of intermediate principal stress, and the failure is dominated by shear fracturing. There are two stages of fracture development: stable propagation stage and unstable failure stage. The AE events occurred in a zone parallel to pre-existing crack plane, and the AE zone increased gradually with the increase of intermediate principal stress, eventually forming obvious shear rupture planes. This shows that shear cracks initiated and propagated in the pre-existing crack direction, forming a shear rupture plane inside the specimens. The paths of fracturing inside the specimens were observed using the Computerized Tomography (CT) scanning and reconstruction.

• 반도체디스플레이기술학회지
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• 제21권2호
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• pp.25-31
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• 2022

By an aid of needle coating, we have fabricated a spherical microlens array using poly(methyl methacrylate) for potential applications in light extraction of organic light-emitting diodes. With an attempt to achieve high-density and high-aspect-ratio microlens arrays, we have investigated the coating behaviors by varying the material parameters such as the solute concentration and wettability of the poly(methyl methacrylate) solution and process parameters such as the dwell time of needle near the substrate, retract distance of needle from the substrate, and coating gap between the needle and substrate. Under the optimized coating conditions, it is demonstrated that high-aspect-ratio microlens arrays can be obtained using a coating solution with high solute concentration and a small amount of a hydrophobic solvent. It is found that the diameter and height of microlens array are decreased with increasing poly(methyl methacrylate) concentration, yet the overall aspect ratio is rather enhanced. By the addition of 5 wt% hexylamine in 35 wt% poly(methyl methacrylate) solution, we have achieved a spherical microlens with the height of 7.7 ㎛ and the width of 94.24 ㎛ (the aspect ratio of 0.082). To estimate the capability of light extraction by the microlens array, we have performed ray tracing simulations and demonstrated that the light extraction efficiency of organic light-emitting diode is expected to be enhanced up to 24%.