• 한국분무공학회지
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• 제12권4호
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• pp.198-203
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• 2007

In the present work, surface wetting effect on spread-splash regime and transition criterion of the water and ethanol droplets impacting an unheated dry wall has been experimentally investigated. The droplet was directed on a polished STS plate and a glass slide, and the impinging behavior was visualized and recorded using a CCD camera. Droplet diameter and velocity approaching the wall were measured as well. The critical Sommerfeld number representing the spread-splash boundary for the ethanol droplet impinging on the substrates turned out to be smaller compared to that for the water droplet impinging on the substrates with the surface roughness condition remained unchanged. The shift of the transition boundary is considered to be due to the effect of the surface wettability represented by static contact angle and surface tension of droplet.

• 마이크로전자및패키징학회지
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• 제7권2호
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• pp.55-62
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• 2000

Si-wafer에 단면 코팅된 UBM(Under Bump Metallurgy)의 젖음성을 Sn-Pb 솔더에서 평가하기 위하여 wetting balance 법을 사용하였다. 단면 코팅된 UBM의 젖음곡선은 양면 코팅된 시편의 젖음 곡선과 비교할 때, 젖음곡선의 모양이 비슷하고 젖음곡선을 특징짓는 변수들의 온도에 대한 변화경향이 일치하였다. 단면 코팅된 금속층의 젖음성을 젖음곡선으로부터 정의한 새로운 젖음 지수 $F_{min}$, $F_{s}t_{s}$로 평가할 수 있었다. Au/Cu/Cr UBM은 젖음시간의 측면에서 Au/Ni/Ti UBM보다 젖음성이 우수하였다 Si-wafer에 단면 코팅된 UBM과 Sn-Pb 솔더의 접촉각을 $F_{s}$와 기울어짐각을 측정하고 메니스커스의 정적상태에서 힘의 평형으로부터 유도된 식을 이용하여 계산할 수 있었다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.671-674
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• 2008

We investigate the slippage effect in a micro-channel depending on the surface characteristics; hydrophilic, hydrophobic, and super-hydrophobic wettabilities. The micro-scale grooves are fabricated on the vertical wall to make the super-hydrophobic surfaces, which enable us visualize the flow fields near walls and directly measure the slip length. Velocity profiles are measured using micro-particle image velocimetry (Micro-PIV) and compared those in the hydrophilic glass, hydrophobic PDMS, and super-hydrophobic PDMS micro-channels. To directly measure the velocity in the super-hydrophobic micro-channel, the transverse groove structures are fabricated on the vertical wall in the micro-channel. The velocity profile near the wall shows larger slip length and, if the groove structure is high and wide, the liquid meniscus forms curves into the valley so that the wavy flow is created after the grooves.

• 한국고분자학회지:고분자과학과기술
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• 제22권3호
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• pp.248-255
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• 2011

• Bulletin of the Korean Chemical Society
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• 제32권8호
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• pp.2623-2627
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• 2011

We investigated the surface structure and wetting behavior of octaneselenolate self-assembled monolayers (SAMs) on Au(111) formed in a 50 ${\mu}M$ ethanol solution according to immersion time, using scanning tunneling microscopy (STM) and an automatic contact angle (CA) goniometer. Closely-packed, well-ordered alkanethiol SAMs would form as the immersion time increased; unexpectedly, however, we observed the structural transition of octaneselenolate SAMs from a molecular row phase with a long-range order to a disordered phase with a high density of vacancy islands (VIs). Molecularly resolved STM imaging revealed that the missing-row ordered phase of the SAMs could be assigned as a $(6{\times}{\surd}3)R30^{\circ}$ superlattice containing three molecules in the rectangular unit cell. In addition, CA measurements showed that the structural order and defect density of VIs are closely related to the wetting behaviors of octaneselenolate SAMs on gold. In this study, we clearly demonstrate that interactions between the headgroups and gold surfaces play an important role in determining the physical properties and surface structure of SAMs.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2009년도 추계학술발표대회
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• pp.25.1-25.1
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• 2009

The effects of surface energyon the wetting transition for impinging water droplets were experimentally investigated on the chemically modified WOx nanowire surfaces. We could modify the surface energy of the nanostructures through chemisorption of alkyltrichlorosilanes with various carbon chain lengths and by the UV-enhanced decomposition of self assembled monolayer (SAM) molecules chemically adsorbedon the array. Three surface wetting states could be identified through the balance between antiwetting and wetting pressures. This approach establishes simple strategy for the design criteria for water-repellent surface to impinging droplets.

• International Journal of Air-Conditioning and Refrigeration
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• 제10권3호
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• pp.147-152
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• 2002

When a liquid is supplied through a nozzle onto a relatively non-wetting inclined solid surface, a narrow rivulet forms. There exist several regimes of rivulet flow depending on various flow conditions. In this paper, the fundamental mechanism behind the transition of a linear rivulet to a droplet flow is investigated. The experiments show that the droplet flow emerges due to the necking of a liquid thread near the nozzle. Based on the observation, it is argued that when the retraction velocity of a liquid thread exceeds its axial velocity, the bifurcation of the liquid thread occurs, and this argument is experimentally verified.

• 한국지반공학회논문집
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• 제23권3호
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• pp.101-109
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• 2007

국내 풍화토사면의 경우 순수 균질 사면보다는 대부분 점토 및 세립분이 섞인 비균질 상태로 존재하며 이러한 함유비율은 풍화도 및 지역에 따라 다르다. 따라서 세립분함량 변화에 따른 불포화사면에의 분석을 위해, 화강풍화토(SW)에 일정비율의 세립분(CH)을 섞어 성형한 시료를 통해 GCTS pressure plates을 이용한 함수특성곡선 실험을 수행하였다. 실험 및 침투해석결과 강우지속시간에 따른 포화깊이의 증가율은 세립분이 증가할수록 또한 상대밀도가 증가할수록 작아졌다. 또한 침투해석과 포화 및 불포화강도정수를 이용한 사면 안정성 해석결과(SLOPE/W), 전반적으로 세립분함량 $10\sim15%$의 범위까지는 침투깊이 증가에 따른 흡수력 변화가 안전율에 지대한 영향을 미치는 반면 이를 초과하는 경우(>15%)에는 오히려 세립분함량 증가에 따른 강도정수의 변화가 크게 영향을 미침을 알 수 있었다.

• 한국표면공학회지
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• 제33권5호
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• pp.373-380
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• 2000

The flow melting behavior of the electrolytic tinplate during reflow treatment was investigated in terms of morphology and structure of coating layers which were electrodeposited with variation of electrolyte temperature. It was commonly found that the nucleation density of the electrodeposits showed little difference with the electrolyte temperature, and the growth of electrodeposited tin occurred along <100> direction of (002) plane. At low electrolyte temperature, the (002) plane of tin nucleated paralleling to the substrate and grew perpendicularly to the substrate, which rendered porous rod-like deposits. With increasing the temperature, the (002) plane nucleated declining $15^{\circ}$ to the substrate and also grew to the normal <100> direction, which enabled lateral growth of the tin crystals and rendered compact deposits. During reflow treatment, the matte deposit transformed to the reflowed state via transition regions consisted of contraction, island formation, and wetting . The matte deposits formed at low temperature exhibited wide transition regions because of poor thermal transfer between crystals due to their porous nature. While that formed at high temperature transformed very rapidly to the reflowed state by enhanced thermal transfer between the compact crystals.

• Journal of Information Display
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• 제11권4호
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• pp.140-143
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• 2010

A simple and versatile method of fabricating color patterns in two-dimension (2D) and three-dimension (3D) was developed using the selective-wettability approach. Red, green, and blue color elements are sequentially formed on a single substrate in a pattern-by-pattern and/or pattern-on-pattern fashion, through a simple coating process. Either 2D or 3D structures in an array format are produced by controlling the thickness of the hydrophobic layer (HL) coating a substrate within the framework of wetting transition. Moreover, it was demonstrated that the stacked geometry of two successive patterns can be easily tailored for various types of color arrays, with the pattern fidelity of a few tens of nanometers in terms of only a parameter of the HL thickness.