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Study of the wetting characteristics of water droplet on a heterogeneous pillared surface
고정안,권태우,매튜스탠리암브로시아,하만영 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.3
We investigated the wetting characteristics of a water droplet on a heterogeneous pillared surface at the nano-scale including contactangle, molecule inflow percentage and density fields and compared them with the wetting characteristics of a water droplet on a homogeneouspillared surface. Molecular dynamics simulations were employed to analyze the wetting behavior of water droplets on surfaceswith pillar structures by considering different potential energies including bond, angle, Lennard-Jones and Coulomb to calculate the interactingforces between water molecules and the surface. The heterogeneous surfaces considered had pillars with a different surfaceenergy than the base surface. It was found that the difference in surface energy between the base surface and pillar had little effect on thehydrophobicity of the surface at low pillar heights. However cases with pillar heights over H = 4.24 Å, the pillar surface energy has alarger effect on the molecule inflow percentage with the maximum differences in the range from 33.8% to 47.2% depending on the basesurface energy. At a pillar height of H = 16.96 Å, the pillar surface energy has a large effect on the contact angle of the water droplet withthe maximum differences in the range from -26.1% to -40.62% depending on the base surface energy. There was a large variation in thecontact angle of the droplet as the pillar height increased when there was a large difference in the surface energies between the base andthe pillars.
나노구조를 가지는 표면에서의 수액적 형성에 대한 분자동역학 시뮬레이션
고정안(Jeong-Ahn Ko),최호진(Ho-Jin Choi),홍승도(Seong-Do Hong),윤현식(Hyun-Sik Yoon),하만영(Man-Yeong Ha) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
In case of the roughness surface, it is well known, the contact angle between the wall and water droplet change. This means that we could control the hydrophilic or hydrophobic property using physical and chemical treatment of the surface. Experimental, theoretical and computational studies have been carried out over the past several decades to research the wetting phenomena of a droplet on the different surface structures. In this study, we study to the variation in contact angle of a nano-sized water droplet on the nano stripe-patterned surface by changing the height and width of the stripe pillar, and the gap width of the stripes.
용매가 전기방사한 Poly(vinyl acetate)(PVAc) 부직포의 형태 및 기계적 특성에 미치는 영향
구자람,고정안,김익수,김환철,김학용,길명섭,Gu, Ja-Ram,Ko, Jung-An,Kim, Ick-Soo,Kim, Hwan-Chul,Kim, Hak-Yong,Khil, Myung-Seob 한국섬유공학회 2010 한국섬유공학회지 Vol.47 No.4
The effect of solvents on the surface morphology and mechanical properties of poly(vinyl acetate) nanofibrous nonwoven via electrospinning was investigated. The fiber diameters decreased with increasing boiling point of the solvents. Among the solvents used in this study, DMF was the best solvent that produced PVAc fibers with the thinnest diameter of ca $0.2\;{\mu}m$. Such a result can be explained by considering the high boiling point of a solvent, allowing sufficient time for a smaller segment of a charged jet during its flight to the collector.
천인범(In Beom Cheon),고정안(Jeong Ahn Ko),윤현식(Hyun Sik Yoon),하만영(Man Young Ha) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
In the present study, the behaviors of nano water droplets were investigated using molecular dynamics simulation. In general, separated nano water droplets merge each other because of interactive force by Lennard-Jones potential and Couloumb potential. We focus on understanding the merging mechanisms of nano droplets. The calculations were extended to droplets having ratio of radii between 0.4 and 1.0 and initial distance between 2A and 8A , respectively. Then, we observed the shape of droplets and time spent on merging. The time spent on merging rises linearly with according to the increasing of droplet ratio as we expected. Also, the time spent on merging is getting increases with according to the increasing initial distance, however, when the initial distance is more than 8A merging time is observed to be perturbed.