• Tribology and Lubricants
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• 제14권4호
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• pp.37-43
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• 1998

The friction loss between piston rings and cylinder liner is due to the tension of the piston rings. Lubricant is usually supplied to reduce the friction. However, the sliding speed of the piston varies during the reciprocating cycle and is very low near TDC(Top Dead Center)/BDC(Bottom Dead Center), where the hydrodynamic lubrication cannot be sustained. Since the lubrication regime is shifted from the hydrodynamic to the boundary lubrication near TDC/BDC, wear particles are easily generated so that the friction loss becomes bigger and bigger due to the plowing effect of wear particles. In this study, for the purpose of reducing the friction loss, an undulated surface is adopted to the cylinder liner to trap wear particles. The friction force variations, which are measured by strain gaged, show that the concept of undulated surface is one of the promising methods to effectively reduce the friction between piston rings and cylinder liner.

• International Journal of Precision Engineering and Manufacturing
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• 제9권3호
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• pp.13-17
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• 2008

This paper deals with the directional mobility of droplets on structured surfaces. Structured surfaces were micro-patterned with rectangular lines and spaces of varying pitch and height in the sub-millimeter range. The material used was polydimethylsiloxane, which is hydrophobic and wettable by oil. First, we studied the effect of the structural design on the sliding angle of pure water or oil through experiments. For pure water droplets, we found that a wider pitch enhanced the directionality. On the other hand, oil droplets spread along the groove because of their low surface tension and strong capillary force. The directionality of the sliding angle of oil droplets was larger than that of pure water, especially when the groove was narrower and deeper. Second, we poured a large amount of liquid on the structure and evaluated the removal rate on the tilted surface. We found that a parallel structure enhanced the liquid mobility for both pure water and oil.

• Food Science and Biotechnology
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• 제16권2호
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• pp.234-237
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• 2007

Water resistance of three biopolyester films, such as poly-L-lactate (PLA), poly-hydroxybutyrate-co-valerate (PHBV), and Ecoflex, and low density polyethylene (LDPE) film was investigated by measuring contact angle of various probe liquids on the films. The properties measured were initial contact angle of water, dynamic change of the water contact angle with time, and the critical surface energy of the films. Water contact angle of the biopolyester films ($57.62-68.76^{\circ}$) was lower than that of LDPE film ($85.19^{\circ}$) indicating biopolyester films are less hydrophobic. The result of dynamic change of water contact angle also showed that the biopolyester films are less water resistant than LDPE film, but much more water resistant than cellulose-based packaging materials. Apparent critical surface energy for the biopolyester films (35.15-38.55 mN/m) was higher than that of LDPE film (28.59 mN/m) indicating LDPE film is more hydrophobic.

• 한국해양공학회지
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• 제29권6호
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• pp.445-453
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• 2015

The stress triaxiality and lode angle are known to be most dominant fracture parameters in ductile materials. This paper proposes a three-dimensional failure strain surface for a ductile steel, called a low-temperature high-tensile steel (EH36), using average stress triaxiality and average normalized lode parameter, along with briefly introducing their theoretical background. It is an extension of previous works by Choung et al. (2011; 2012; 2014a; 2014b) and Choung and Nam (2013), in which a two-dimensional failure strain locus was presented. A series of tests for specially designed specimens that were expected to fail in the shear mode, shear-tension mode, and compression mode was conducted to develop a three-dimensional fracture surface covering wide ranges for the two parameters. This paper discusses the test procedures for three different tests in detail. The tensile force versus stroke data are presented as the results of these tests and will be used for the verification of numerical simulations and fracture identifications in Part II.

• 한국지하수토양환경학회지:지하수토양환경
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• 제15권6호
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• pp.37-45
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• 2010

Surfactant-enhanced ozone sparging (SEOS), an advanced version of SEAS (surfactant-enhance air sparging) was introduced in this study for the first time for removal of non-volatile contaminant from aquifer. The advantages of implementing SEAS, enhanced air saturation and expanded zone of sparging influence, are combined with the oxidative potential of ozone gas. Experiments conducted in this study were tow fold; 1-dimensional column experiments for the changes in the gas saturation and contaminant removal during sparging, and 2-dimensional box model experiment for the changes in the size of zone of influence and contaminant removal. An anionic surfactant (SDBS, sodium dodecylbenzene sulfonate) was used to control surface tension of water. Fluorescein sodium salt was used as a representative of watersoluble contaminants, for its fluorescence which is easy to detect when it disappears due to oxidative degradation. Three different gases (air, high-concentration ozone gas, and low-concentration ozone gas) were used for the sparging of 1-D column experiment, while two gases (air and low-concentration ozone gas) were used for 2-D box model experiment. When SEOS was performed for the column and box model, the air saturation and the zone of influence were improved significantly compared to air sparging without surface tension suppression, resulted in effective removal of the contaminant. Based on the experiments observations conducted in this study, SEOS was found to maintain the advantages of SEAS with further capability of oxidative degradation of non-volatile contaminants.

• 공업화학
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• 제31권2호
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• pp.193-199
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• 2020

식기세정용 세정제의 조성에 따른 오일(O) 및 세정수용액(W)의 계면의 물성에 미치는 영향을 조사하였으며 계면물성에 따른 세정효과를 검토하였다. 또한 각 조성에 따른 식기표면에 오염된 오일의 세정력과 세척 헹굼 후 오염물 및 세척제의 잔류성에 대한 평가를 하였다. 본 연구에서 사용된 세정제의 조성에 있어서 고체표면에 오염된 오일의 제거는 세척액/오일/고체 간의 계면물성과 깊은 관련이 있었으며, 특히 전진 및 후진 동적접촉각에 크게 의존하였다. 전진 및 후진접촉각이 동시에 낮은 경우에 세정액의 침투성이 매우 커서 고체표면에 오염된 오일의 제거효과가 높았으며 세척 후 오염물의 잔류가 거의 없었다. O/W의 계면장력이 작을수록 오염된 오일의 유화가 잘 되었으며 계면장력이 높을수록 유화가 잘 이루어지지 않았다. 그러나 본 연구에서는 유화효과는 세척력에 크게 영향을 미치지 못하였으며 특히 낮은 계면장력을 갖는 세정제의 경우 세척 후 세정제 물질이 피세척물의 표면에 잔류하는 문제점이 있었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.130-130
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• 2016

Bioinspired hierarchical nanostructures for self-cleaning s-tnwjurface and SERS substrates are investigated. The multi-level hierarchy is combined with CuO nanowire and additional nanoscale structures. CuO nanowire, which has extremely high aspect ratio, serves as a base structure of multi-level hierarchy and additional flower like structures are placed on the CuO nanowires. Since as-fabricated CuO nanostructures are hydrophilic, the surface is coated with perfluorooctyltrichlorosilane in order to change its wetting property to hydrophobic. While those CuO based nanostructures have a sufficient roughness for superhydrophobic characteristics, hierarchical nanoflowers on nanowire structures lead to a self-cleaning surface. Furthermore, flower like nanostructures provide reentrant curvatures, thus enabling oleophobic property. The surfaces has a repellency even for a tiny droplet (10 nL) of low surface tension liquids (~35 mN/m). On the on hands, nanoflowers provide many number of nanoscale gaps. After a thin layer of silver is deposited on the surface of CuO nanostructures, those nanoscale gaps act as hot-spot for surface enhanced Raman scattering (SERS). To analyze SERS enhancement of the surfaces, Raman shift is measured with varying molar density of 4-Mercaptopyridine from mM to pM. From these results, hierarchical CuO nanostructures are suitable for self-maintenance and cost effective SERS sensing applications.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.774-778
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• 2004

The atomization process of a circular $SF_{6}$ liquid jet issued into an otherwise quiescent, high-pressure $N_2$ gas was observed to explore the breakup mechanism of liquid ligaments involved in turbulent atomization. Both liquid and gas temperatures were fixed at a room temperature but the gas pressure was elevated to more than twice the critical pressure of $SF_{6}$. Therefore, the liquid surface was in a thermodynamic state close to a critical mixing condition with suppressed vaporization. Since the surface tension and the surface gas density approach zero and the surface liquid density, respectively, phenomena equivalent to those which would appear when a very high speed laminar flow of water were injected into the atmospheric-pressure air can be observed by issuing $SF_{6}$ liquid at low speeds in micro-gravity environment which avoid disturbances due to gravity forces. The instability ob near-critical mixing surface jet was quantitatively characterized using a newly developed device, which could issue a very small amount of $SF_{6}$ liquid at small constant velocity into a very high-pressure $N_2$ gas.

• 공업화학
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• 제22권1호
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• pp.37-44
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• 2011

합성한 sorbitan laurate SP 20의 CMC 값은 약 $7.216{\times}10^{-4}mol/L$로서 옥틸페놀 에톡실레이트 OPE 10에 비하여 약간 크지만, CMC에서의 표면장력은 26.0 mN/m로 OPE 10에 비하여 작았다. 또한 SP 20의 경우에는 OPE 10 계면활성제와 비교하며 공기와 수용액의 계면이 계면활성제 단분자에 의하여 포화되는 데 더 많은 시간이 소요되었다. SP 20 계면활성제 수용액의 접촉각은 계면활성제 농도가 증가함에 따라 감소하였으며, 동일한 계면활성제 농도에서 OPE 10에 비하여 접촉각이 큼을 알 수 있었다. OPE 10과 SP 20 계면활성제 수용액의 거품 반감기는 각각 770, 1268 s로서 SP 20 계면활성제가 OPE 10 계면활성제에 비하여 거품의 안정성이 크며, 이러한 결과는 표면장력 측정 결과와 일치하였다. OPE 10에 비하여 SP 20의 가용화 속도는 매우 낮으며, 이러한 결과는 foam stability, 접촉각 및 CMC 실험 결과와 일치하였다. OPE 10과 SP 20 시스템의 평형에서의 계면장력은 각각 0.659, 0.742 mN/m으로서 비슷한 값을 나타내었으나, OPE 10의 경우에는 비교적 짧은 시간 내에 계면장력이 평형에 도달하는 것에 비하여 SP 10의 경우에는 계면장력이 평형 값에 도달하는데 약 25 min이 소요되었다.

• 보존과학회지
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• 제24권
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• pp.37-42
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• 2008

유구 이전의 안정성은 고분자 재료의 물리적 우수성뿐만 아니라 작업성과도 밀접한 관계가 있다. 이들 유구 이전 재료들은 토양에 함유된 수분 함량이나 낮은 온도와 같은 주위 환경의 영향이 없이 작업이 가능해야 하며, Epoxy최종 생성물로부터 Urethane 1차 생성물을 박리시키는 작업 공정 중의 안정성과 작업성도 요구된다. 그래서 본 논문에서는 우수한 물리적 특성을 갖는 저점도의 Epoxy polymer와 경화제 및 유구 이전을 위한 박리제에 대한 합성에 대하여 보고하고자 한다. 이 유구 이전 전용 저점도 Epoxy는 우수한 접착 강도와 자체 강도, 작업성 등의 물리적 안정성을 유지하고 있으며 특히, 박리제는 우레탄과 저점도의 Epoxy 간의 우수한 박리 안정성을 나타내고 있다.