• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 추계학술대회 논문집 전기물성,응용부문
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• pp.6-8
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• 2001

This report describes the effect of the blending of poly(trifluoropropylmethylvinylsiloxane) (PTFPMVS) with poly(dimethylsiloxane) (PDMS) on the surface properties such as water repellency using dynamic contact angle (DCA) measurement. We have investigated the surface molecular mobility of the PDMS/PTFPMVS blends via a DCA measurement and an adhesion tension relaxation. It could be shown that a flexible side-chain segment in PTFPMVS having higher surface energy, could be reoriented easily in water to decrease the interfacial tension of the polymer/water interface, which seems to play a major role at the decrease of the receding contact angle and the surface resistivity of PDMS/PTFPMVS blends.

• 대한기계학회논문집A
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• 제32권2호
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• pp.143-147
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• 2008

Super-hydrophobic surfaces showed that contact angle of water was higher than 140 degrees. That surface could be made several methods such as Carbon nano tubes grown vertically, PDMS asperities arrays, hydrophobic fractal surfaces, and self assembled monolayers coated by CVD and so on. However, we fabricated super-hydrophobic surfaces with plasma treatments which were very cost efficient processes. Their surfaces were characterized by static contact angles, advancing, receding, and stability against UV irradiation. Optimal surfaces showed static contact angles were higher than 150 degrees. Super-hydrophobic property was remained after UV irradiation for one week.

• 한국전산유체공학회지
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• 제12권3호
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• pp.41-46
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• 2007

Dynamic behavior of immiscible gas bubble attached to the wall in channel flow plays very important role in many engineering applications. Special attention has been paid to micro direct methanol fuel cell(${\mu}$DMFC) where surface tension becomes dominant factor with minor gravitational effect due to its reduced size. Therefore, displacement of $CO_2$ bubble generating on a cathode side in ${\mu}$DMFC can be very difficult and efficient removal of $CO_2$ bubbles will affect the overall machine performance considerably. We have focused our efforts on studying the dynamic behavior of immiscible bubble attached to the one side of the wall on 2D rectangular channel subject to external shear flow. We used Level Contour Reconstruction Method(LCRM) which is the simplified version of front tracking method to track the bubble interface motion. Effects of Reynolds number, Weber number, advancing/receding contact angle and property ratio on bubble detachment characteristic has been numerically identified.

• 접착 및 계면
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• 제15권2호
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• pp.57-62
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• 2014

피타고라스 원리를 이용하면 특정 도형이 보유하고 있는 각도에 대한 계산이 용이해진다. 정적 접촉각 평가방법을 이용할 경우 용액과 고체 물체간의 접촉각의 수치 계산이 가장 중요한 부분이다. 용액과 고체 표면이 이루는 각도 측정을 용이하게 하기 위해서 접촉각을 계산하는 방법을 규격화하는 방법과 접촉각 평가에 따른 실험적 변수 최소화 조건을 마련하였다. 접촉각 실험을 위한 용액의 직경에 따른 접촉각의 각도 계산 오차를 분석하고, 최적의 물방울 직경은 1 mm임을 확인하였다. 피타고라스 원리를 이용한 접촉각 측정방법은 전진각과 후진각을 확인하는데 사용할 수 있으며, 소수성 및 친수성 표면을 분석하는데 적용이 가능하였다. 궁극적으로 일반적인 접선 긋기를 통한 각도 계산 결과보다 피타고라스 원리를 이용하여 접촉각 각도 계산을 실시할 경우 비교적 정확한 접촉각 계산 결과를 확인할 수 있었다.

• 한국가시화정보학회지
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• 제19권3호
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• pp.15-21
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• 2021

In this study, we investigated the dynamics of a droplet impacting rough hydrophobic surfaces through high-speed imaging. Micrometer-sized structures with grooves and pillars were fabricated on smooth Polydimethylsiloxane (PDMS) surfaces by laser ablation. We used Newtonian and non-Newtonian liquid droplets to study the drop impact dynamics. De-ionized water and aqueous glycerin solutions were used for the Newtonian liquid droplet. The solutions of xanthan gum in water were prepared to provide elastic property to the Newtonian droplet. We found that the orientation of the surface structures affected the maximal spreading diameter of the droplet due to the degree of slippage. During the droplet retraction, the dynamic receding contact angles were measured to be around 90° or less. It resulted in the formation of the micro-capillary bridges between the receding droplet and the surface structures. Then, the rupture of the capillary bridge led to the formation of micrometer-sized droplets on top of the surface structures. The size of the microdroplets was found to increase with increasing the impacting velocity and viscosity of the Newtonian liquid droplets. However, the size of the isolated microdroplets decreased with enhancing the elasticity of the droplets, and the size of the non-Newtonian microdroplets was not affected by the impacting velocity.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2967-2970
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• 2007

In a usual painting process, a liquid drop spreads on canvas by being dragged along a paintbrush. To obtain the fundamental understanding of the painting process from the mechanical point of view, we experimentally investigate various dynamic behavior of a liquid drop that spreads between moving solid plates. It is shown that three distinct types of drop spreading take place, i.e. shearing, spreading, and intact dragging, depending on the liquid viscosity and surface tension, the plate speed, and the wettability. We suggest a regime map based on the capillary number and the receding contact angle, which indicates the boundaries between different types of spreading behavior in a dimensionless space.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.175-180
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• 2002

Loading/Unloading(L/UL) mechanism has been considered to be an alternative to contact start-stop(CSS) mechanism which eliminates stiction and wear associated with frequent start and stop process. It has other advantages including increased areal density due to lower flying height, reduced power consumption, and improved shock resistance. In order for L/UL to be Implemented in Near-field recording system properly, dynamics of optical flying head must be understood and optimized. In this paper the dynamic characteristics during loading process is analyzed numerically to investigate the effect of design parameters such as loading speed. slider shape, and initia conditions on the dynamic reponses of flying head..

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2648-2653
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• 2007

Recently, increasing demand on not only lighter but also extremely mobile battery make micro fuel cell device very attractive alternative. By reducing the size of fuel cell, surface tension becomes dominant factor with minor gravitational effect. Therefore, it is very difficult to detach the $CO_2$ bubble generating on a cathode side in ${\mu}DMFC$ (micro direct methanol fuel cell). The degassing of a $CO_2$ bubble has drawn quite attention especially for ${\mu}DMFC$ due to its considerable effect on overall machine performance. Our attention has been paid to the dynamic behavior of immiscible bubble attached to the one side of the wall on 2D rectangular channel subject to external shear flow. We use Level Contour Reconstruction Method (LCRM) which is simplified version of front tracking method to track the bubble interface motion. Effects of Reynolds number, Weber number, advancing/receding contact angle and property ratio on bubble detachment characteristic has been numerically identified.

• Journal of Mechanical Science and Technology
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• 제20권11호
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• pp.1980-1992
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• 2006

Nucleate pool boiling experiments were performed using pure R11 for various surface angles under constant heat flux conditions during saturated pool boiling. A 1-mm-diameter circular heater with an artificial cavity in the center that was fabricated using a MEMS technique and a high-speed controller were used to maintain the constant heat flux. Bubble growth images were taken at 5000 frames per second using a high-speed CCD camera. The bubble geometry was obtained from the captured bubble images. The effects of the surface angle on the bubble growth behavior were analyzed for the initial and thermal growth regions using dimensional scales. The parameters that affected the bubble growth behavior were the bubble radius, bubble growth rate, sliding velocity, bubble shape, and advancing and receding contact angles. These phenomena require further analysis for various surface angles and the obtained constant heat flux data provide a good foundation for such future work.

• 한국태양에너지학회 논문집
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• 제29권4호
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• pp.7-14
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• 2009

Nucleate pool boiling experiments with constant heat flux condition were performed using pure R11 and R113 for various surface angles under saturated pool condition. A circular heater of 1 mm diameter, with artificial cavity in the center, fabricated using MEMS technique and the high-speed controller were used to maintain the constant heat flux. Images of bubble growth were taken at 5,000 frames per second using a high-speed CCD camera. The bubble geometry was obtained from the captured bubble images. The effects of surface angles on the bubble growth behaviors were analyzed as dimensional scales for the initial and thermal growth regions. The parameters for the bubble growth behaviors were bubble radius, bubble growth rate, sliding velocity, bubble shape and advancing and receding contact angles. These phenomena require further analysis for various surface angles, but this study will provide good experimental data with constant heat flux boundary condition for such works.