친환경적인 전기자동차, 전기 추진 선박, 하이브리드 자동차, 전철 등의 구성 요소 중 기존 파워 디바이스에서 사용 중인 실리 콘(Si)을 실리콘 카바이드(SiC, silicon carbide)로 대체하려는 연구가 진행 중이다. 고품질의 SiC 결정 성장을 시키기 위해 다양한 방법 중 상 부 종자 용액 성장(top seeded solution growth, TSSG)법이 큰 주목을 받고 있다. 그러나 SiC 결정 성장 시, 느린 성장 속도뿐만 아니라 많은 결함을 갖는 문제를 갖고 있다. 그래서 본 연구에서는 SiC 단결정을 성장 시키는 TSSG법의 개선을 위한 기초 연구를 진행하였다. 기존에 많이 사용되는 Si, Si0.6Cr0.4 용융 물질와 탄소 도가니와 관계를 가열 온도에 따른 접촉각과 자연 냉각 후 시료의 단면의 차이점을 통해 비 교 분석하였다. 젖음성 분석 시험 장비를 이용하여 탄소 도가니로 쓰이는 카본판 위에 Si과 Si0.6Cr0.4를 놓고 가열 및 용융 시키며 접촉각의 변화를 측정하였고, 가열 종료 후 자연 냉각된 시료의 단면을 관찰하였다. 결과적으로 1800 ℃에서 Si, Si0.6Cr0.4와 탄소판 간의 접촉각이 10°정도 차이를 나타냈다. 단면 관찰에서는 Si의 경우, 탄소판 안으로 스며든 후 굳은 모습을 확인할 수 있었다. 반면, Si0.6Cr0.4의 경우는 탄 소판 안으로 스며든 범위가 훨씬 더 적게 나타냈다. 본 연구의 결과는 TSSG법을 활용한 SiC 단결정 성장을 위한 연구의 기초 자료로 활용 될 것으로 기대된다.

The volume of fluid method is used to investigate the behavior of a liquid water slug in a PEMFC trapezoidal gas channel(GC) with a open angle of 60 degrees. To evaluate the effect of the contact angle of the top and side walls, the gas diffusion layer water coverage ratio(GWCR) and water volume fraction(WVF) in a inspection control volume are analyzed. As the contact angle increases, GWCR increases and WVF decreases. The cases with the GC contact angle of 60 and 80 degrees show the more favorable water removal characteristics compared to the other cases in a GC flooding condition.

The volume of fluid method is applied to study the effects of the gas channel wall contact angle on the removal characteristics of a water slug in a right angle PEMFC gas channel. While maintaining the same GDL surface contact angle, two different contact angle distributions on the control area in the corner region are compared via the water coverage ratio and water volume fraction. The water coverage ratios of the hydrophobic channel corner case mainly show smaller values than that of the hydrophilic case except around 27 ms. The water volume fraction of the hydrophobic corner case is supposed to drop down quickly around 27 ms due to the dynamic movement of the liquid water compared to the hydrophilic case. In overall, the hydrophobic corner case shows better water slug removal characteristics.

To study the effects of the gas channel wall contact angle on the behavior of a liquid water slug, numerical simulations are performed with the volume of fluid (VOF) method. Two different contact angle combinations on the side and top channel walls are selected. In comparison to the reference case, the water slug is removed faster when the hydrophobic contact angle is applied selectively in the corner section.

Hydrophilic SiO2 layers were obtained by the atmospheric-pressure plasma treatment. Superhydrophobic SiO2 layers were first deposited by the electrospray deposition method. The electrospunable solution that was prepared based on the solgel method was sprayed on Si (100) substrates. The surface of the electrosprayed SiO2 layers consisted of the agglomeration of nano-sized grains, which led to a very high roughness and revealed a very high contact angle to water droplets over 162˚. After having been exposed to the atmospheric Ar/O2 plasma, the observed superhydrophobicity of the SiO2 layers were greatly changed: a dramatic variation of the water contact angle from 162˚ to 3˚, namely realization of superhydrophillicity. Interestingly, the surface microstructure was almost preserved. According to the XPS analysis, it is more likely that thanks to the plasma exposure, the surface of SiO2 layers will be cleaned in terms of organic species that are hydrophobic-inducing, consequently leading to the hydrophilic nature observed for the plasma-exposed SiO2 layers.

Generally, in the previous researches, it is found that a water droplet is respectively in Wenzel and Cassie-Baxter states on hydrophilic/hydrophobic rough surfaces. And Wenzel and Cassie-Baxter equations are used to estimate the apparent contact angle on the surfaces. However, difference between measured apparent contact angle and estimated apparent contact angle with the equations is recently reported and new model to estimate apparent contact angle on rough surfaces is proposed. In this study, wetting state and apparent contact angle on the surfaces with micro-pillars should be investigated to find solution of this argument. Using the high resolution microscope, the wetting state of the D.I.water droplet on the surface with micro-pillars was visualized and apparent contact angle of the D.I.water droplet was measured. On the basis of experimental data, the equations to estimate apparent contact angle were verificated and the general wetting characteristics on the surfaces with micro-pillars are finally classified.

목 적: 단백질 침전물이 콘택트렌즈의 함수율, 산소투과성 및 접촉각에 미치는 영향을 조사하였다. 방 법: Polymacon과 etafilcon A 재질의 소프트콘택트렌즈를 착용기간에 따라 수집하여 단백질 침전물을 추출하고 fluorometer를 이용하여 단백질 침전물을 정량하였다. 사용하지 않은 polymacon과 etafilcon A 콘택트렌즈를 lysozyme과 albumin 단백질이 포함된 인공눈물에 넣어 일정하게 단백질을 부착시키고 부착된 단백질 침전물을 정량한후 중량측정법, 전기분해 자동분석법 및 sessile drop 방법을 사용하여 함수율, 산소투과성 및 접촉각을 측정하여 대조군과 비교하였다. 결 과: Polymacon 재질의 콘택트렌즈에 부착된 단백질 침전물 양은 착용기간에 따라 차이가 없었으나, etafilcon A 재질의 콘택트렌즈는 착용기간에 따라 빠르게 증가하였다. 일정하게 단백질을 부착시킨 소프트 렌즈의 경우 함수율은 polymacon 렌즈와 etafilcon A 렌즈에서 모두 감소하였고, 산소투과성도 polymacon 렌즈와 etafilcon A 렌즈에서 모두 감소하였으며 접촉각은 polymacon 렌즈와 etafilcon A 렌즈에서 모두 증가하였다. 결 론: 소프트콘택트렌즈에 부착된 단백질 침전물은 렌즈의 함수율과 산소투과성을 저하시키고 접촉각을 증가시켜 콘택트렌즈 착용 시 불편감을 유발하는 원인이 될 수 있으며 특히 고함수 이온성 재질인 etafilcon A의 경우 더욱 문제가 될 것으로 사료된다.

Testing device was newly designed and built to measure the dynamic contact angle. The measurement was made using microscope interfaced with computerized image analysis system while the dynamic condition being controled using Instron. As specimens for the experiment, two different types of fibers, i.e., hydrophilic and hydrophobic, were prepared. In case of hydrophilic fiber, the increase of twist level gave the increase of contact angle. However, in hydrophobic yarn the increase of twist level gave the decrease of contact angle. When saline was used as a telling liquid, the increase of the concentration gave the increase of contact angle. The results rationalized clearly on the basis of known concepts could be used in designing fabric structure for the improvement of comport performance.