• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.15-18
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• 2006

Recently, experimental visualization of microscale fluid transport has attacted considerable attention in designing microelectromechanical systems. Fluid-surface interactions on hydrophobic and hydrophilic surfaces can play a key role in passively controlling microfluidics. Here we investigate the slip boundary condition depending on the surface characteristics; hydrophilic, hydrophobic wettabilities. Using the micro-PIV, velocity profiles are measured in the glass (hydrophilic), PDMS (hydrophobic) microchannels.

• Applied Chemistry for Engineering
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• v.30 no.3
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• pp.308-312
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• 2019

Amphiphilic gold nanoparticles were synthesized by the functionalization of gold nanoparticles with hydrophilic and hydrophobic ligands on their surfaces, which can be applied to many disciplines such as biology, photonics, electronics, and so on. The ratio of hydrophilic and hydrophobic ligands plays an important role in such applications since the ratio is closely related to physiochemical properties of the nanoparticles. In this paper, the effect of temperature during the ligand exchange reaction on the ratio of ligands on the gold nanoparticle surface was investigated. Hydrophilic ligands have higher affinity to the nanoparticle surface with an increase of the temperature. Furthermore, the amphiphilic nanoparticles at a higher temperature were more soluble in an aqueous solution even with a lower hydrophilicity of the nanoparticle surface.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.327-327
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• 2011

DLC 필름은 바이오 적합성, 특히 생체 적합성이 뛰어나기 때문에 바이오 코팅분야에서 널리 이용된다. 많은 연구 결과에 의하면 세포와 장기 등이 바이오 재료 표면에 적절히 접합할 수 있도록, 재료 표면을 산소나 질소를 이용하여 플라즈마 처리로 초친수성 표면으로 개질하고 있다. 하지만, 시간이 지남에 따라서 친수성 표면은 점차 재료의 표면 처리 전의 성질인 소수성을 회복하게 된다. D실제 생체에 적용하기 위해서 이러한 시효 효과에 대한 정확한 평가가 이루어져야 한다. 따라서 산소와 질소 플라즈마 처리 후의 친수성 성질이 소수성 성질로 변해가는 거동을 조사하는게 중요하다. 13.56 MHz의 plasma assisted chemical vapor deposition (PACVD) 법을 이용하여 DLC와 Si-DLC를 500 ${\mu}m$ 두께의 P-type 실리콘(100) 기판에 증착하였다. 박막 증착 과정에 사용한 기체는 벤젠과 희석된 silane이 사용되었다(SiH4/H2=10:90). 박막 증착은 -400 V의 바이어스 전압을 인가하였으며, 이때 증착 압력은 1.33Pa으로 일정하게 유지하여, 두께 $0.55{\pm}0.01{\mu}m$로 증착하였다. X-ray Photoelectron Spectroscopy (XPS) 법을 이용하여 실리콘 함량을 측정하였으며, 증착 된 Si-DLC의 실리콘 함량은 0~4.88 at. %였다. 이후에 질소와 산소 플라즈마를 이용하여 챔버 압력을 1.33 Pa로 유지하여, -400 V의 바이어스 전압을 인가하여 10분간 표면 처리를 하였다. 표면 처리된 DLC와 Si-DLC 표면 위에서의 물방울(water droplet)의 젖음각을 20일간 측정하였다. 플라즈마 표면 처리 된 모든 시편에서 초기 젖음각은 $10{\sim}20^{\circ}$의 친수성 성질을 보였지만, 점차 젖음각이 상승하여 산소 플라즈마 처리 된 Si-DLC를 제외하고는 5일이 지나면서 거의 소수성 표면으로 회복되었다. 산소 플라즈마 처리 된 Si-DLC의 경우, 젖음 각 측정 기간(20일) 동안 $15^{\circ}$ 미만의 친수성 성질을 유지하였다.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.46 no.1
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• pp.57-65
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• 2020

To prevent loss of hair protein during hair washing process by water through, a shield coating the pathway of water molecules was studied. Hydrophobic virgin hair, hydrophilic hair, which was damaged only methyleicosanoic acid (18-MEA) on the surface, and a repaired hair re-bound 18-MEA, were prepared and water mass changes by as heat were measured. Results showed that hydrophobic hairs followed bi-exponential function of 39 s and 151 s and other two hairs exhibited fast- and mono-exponential decay with 83 s, reflecting the extraction of water molecules without any resistance at the hydrophobic surface. On the assumption that hydrophobic surface resists an extraction of protein in water during the wash, the protein concentrations were compared from the hair of hydrophobic and hydrophilic surface. The extracted hair proteins were 179 and 148 ㎍/mL from the hair coated with hydrophilic polyethylene glycol (PEG) and hydrophobic polydimethylsiloxane (PDMS), respectively. This study suggested that hydrophobic coating on the hair surface could be used to prevent protein loss in wash, represented by LFM. In conclusion, this research provides some useful information to contribute to the development of hair washing products that can prevent protein loss in the cleaning process by granting hydrophobic coatings.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.3
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• pp.263-270
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• 2014

A fluid transport technique is a key issue for the development of microfluidic systems. In this paper, a new concept for transporting a droplet without external power sources is proposed and verified numerically. The proposed device is a heterogeneous surface which has both hydrophilic and hydrophobic horizontal surfaces. The numerical simulation to demonstrate the new concept is conducted by an in-house solution code (PowerCFD) which employs an unstructured cell-centered method based on a conservative pressure-based finite-volume method with interface capturing method (CICSAM) in a volume of fluid (VOF) scheme for phase interface capturing. It is found that the proposed concept for droplet transport shows superior performance for droplet transport in microfluidic systems.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.2096-2098
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• 2004

본 논문은 마이크로 유체 소자의 소재로서 많이 쓰이고 있는 poly(dimethyl-siloxane) (PDMS)의 친수성 유지를 위한 표면 개질에 대한 연구이다. PDMS는 유연성, 투명성 등의 다양한 장점을 가지고 있으나, 높은 소수성으로 인하여 유체 소자로의 응용에 제한을 갖는다. 기존 연구에서 수행한 산소 플라즈마 후 2-Hydroxyethyl methacrylate (HEMA) 처리에 의한 PDMS의 표면 개질은 친수성 유지 시간에 한계가 있었다. 이에 친수성 유지 시간을 증가시키기 위하여 경화된 PDMS에 두 시간의 오존 처리 후, 6시간 동안 monomethyl ether hydroquinone (MEHQ)가 제거된 HEMA로 표면을 개질한다. 표면 처리된 PDMS의 친수성 특성을 확인하기 위해 접촉각을 측정하였다. 측정 결과, 오존을 이용하였을 때 $60^{\circ}$ 이하의 낮은 접촉각이 900시간 이상 유지됨을 확인하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.103-104
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• 2005

본 논문에서는 Nd:YAG($\lambda$=266 nm, pulse) 레이저빔을 PDMS 표면에 조사하여, 소수성 물질인 PDMS를 친수성 물질로 개질하였다. 이미 산소 플라즈마를 이용한 것과 오존을 이용한 PDMS 표면 개질에 관한 논문이 발표되었는데, 레이저를 이용한 표면 개질은 간단한 레이저 빛의 조사만으로 표면을 개질할 수 있는 장점이 있다. 본 논문에서는 레이저를 이용하여 PDMS 를 표면처리한 후에 접촉각 측정기를 이용해서 측정한 결과 접촉각 감소가 있었다. 묘면에 산소 함유량이 증가한 것을 확인함으로써 친수성 물질로의 표면 개질됨을 확인할 수 있었다.

• Journal of the Korean Society for Marine Environment & Energy
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• v.16 no.2
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• pp.82-87
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• 2013

Effects of material surface property, hydrophobic or hydrophilic, on the bio-fouling occurred on the bodies submerged in the sea water are investigated experimentally. 4 test models are used in the experiment, which includes aluminum foil in common use, AAO applied hydrophobic surface, HDFS coated hydrophobic surface and hydrophilic surface. Hydrophobic surfaces with numerous micro & nano-scale pillars on it seems to play very important role of preventing them from fouling in initial stage while the effects disappear in long term sense of fouling process. It is concluded that the surface hydrophobicity retards the initial fouling until the fouling thickness is smaller than the heights of the pillars on it but the effects diminish with the fouling proceeds so that the thickness grows bigger than the pillar heights.

• Korean Chemical Engineering Research
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• v.45 no.5
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• pp.500-505
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• 2007

The objectives of this research were to (1) identify the membrane fouling potential due to different fractions of NOM (2) correlate the physicochemical properties of NOM and membranes with the adsorption of humic substances on membrane (4) find out the effect of membrane physical and chemical washing according to membrane material. The static adsorption test and adsorption test showed that hydrophobic organics adsorbed much more quickly than hydrophilic organics. In case of the effect of membrane properties on the adsorption of organic fractions, the adsorption rate ratio(a) of hydrophobic membrane (0.016, 0.077) was greater than that of hydrophilic membrane (0.010, 0.033) regardless of the kind of organic fractions. This suggests that the UF membrane fouling were occurred mainly by internal pore size decreasing due to adsorption of organic into pore surface for hydrophobic membrane, and by sieving of organics and forming a gel layer on the membrane surface for hydrophilic membrane. In conclusion, the decrease in the pore volume, which was caused by the organic adsorption into the internal pore, was greater with the hydrophobic membrane than with the hydrophilic membrane. In case of the effect of membrane properties on permeate flux, the rate of flux decline for the hydrophobic membrane was significantly greater than that for the hydrophilic membrane.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.6
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• pp.513-523
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• 2014

A fluid transport technique is a key issue for the development of microfluidic systems. In this study, the movement of a droplet on horizontal hydrophilic/hydrophobic surfaces, which is a new concept to transport droplets without external power sources that was recently proposed by the author, was simulated using an in-house solution code(PowerCFD). This code employs an unstructured cell-centered method based on a conservative pressure-based finite-volume method with interface capturing method(CICSAM) in a volume of fluid(VOF) scheme for phase interface capturing. The droplet transport mechanism is examined through numerical results that include velocity vectors, pressure contours, and total kinetic energy inside and around the droplet.