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소수성 DLC 박막으로 코팅된 이중 나노 구조 표면의 적심 거동
차태곤(Tae-Gon Cha),이진우(Jin Woo Yi),이광렬(Kwang-Ryeol Lee),문명운(Myoung-Woon Moon),김호영(Ho-Young Kim) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Solid surface wettability can be controlled by chemical treatment of the material surface or modification of the surface topology. Superhydrophobic surfaces, having the water contact angle close to 180 degrees, have drawn much attention owing to its potential applications for water-repellent self cleaning surfaces, surface energy induced drop motion, and flow channels of low resistance for microfludics devices, etc. We showed earlier the superhydrophobic wetting behavior of a water droplet on nano-scale dual rough surfaces with hydrophobic DLC films. Here we report the results of systematic experiments of the evaporation of a water droplet on the superhydrophobic dual rough surfaces to measure the time evolution of the contact angle induced by the change of the Laplace pressure. The transition condition from Cassie-Baxter mode to Wenzel mode in the droplet wetting behavior was analyzed and compared with that of other superhydrophobic surfaces. The effectiveness and superhydrophobicity of the dual rough structure was also discussed.
차태곤(Tae-Gon Cha),이진우(Jin Woo Yi),이광렬(Kwang-Ryeol Lee),문명운(Myoung-Woon Moon),김호영(Ho-Young Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
To achieve the hierarchy of roughness as observed in lotus leaves, most artificial water-repellent surfaces have nano-asperities on top of micropillars. However. observation of real lotus leaves through SEM reveals that nanoscale roughness covers the entire surface including the base as well as bumps. Thus we fabricate surfaces having the same hierarchical roughness structure as the lotus leaf by forming nanopillars on both micropillars and base. We compare the measures of water-repellency (static contact angle, contact angle hysteresis, and transition pressure between the Cassie and Wenzel states) of the lotus-like surface with those of surfaces having single micro- and nano-roughness. The results show that nanoscale roughness covering entire surface area leads to superior water-repellency to other surface roughness structures. We also give a theoretical consideration of this observation.
문명운(Myoung-Woon Moon),차태곤(Tae-Gon Cha),이광렬(Kwang-Ryeol Lee),Ashkan Vaziri,김호영(Ho-Young Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
Inspired by the gecko's footpad structure, we developed a method to create tilted micropillars on the surface of an elastomeric polymer mimicking the geometry of gecko's setae. The method combines son lithography to create straight micropillars and ion beam irradiation to tilt the straight micropillars in a controlled fashion. We experimentally quantify the asymmetric adhesion and friction characteristics of the fabricated tilted micropillars as a function of the tilting angles. The tilting angle of the pillars was varied by changing the incident angle and duration of the ion beam irradiation. Potential applications of the developed pattern include non-wetting painting and switchable adhesion essential in wall-climbing robots.
플라즈마 DLC 증착법을 이용한 실리콘 표면의 친수성 유지
이진우(Jin Woo Yi),문명운(Myoung-Woon Moon),이광렬(Kwang-Ryeol Lee),김해리(Hae-Ri Kim),김성진(Seong Jin Kim),차태곤(Tae-Gon Cha),김호영(Ho-Young Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
Aging behavior of wettability of Si-DLC (Si incorporated diamond-like carbon) films treated by various gas (H₂, O₂, and N₂) plasma was investigated. We found that the initially low contact angle of most plasma-treated Si-DLC surfaces recovered its high value (near 90°) within few days. However, the contact angle of Si-DLC with the Si weight fraction of 1.24 and 2.66% was measured to be below 10° as-modified, and maintained its value below 15° for 20 days. XPS analysis reveals that the polar components of Si-O bonds, enhancing hydrophilicity, have been almost unchanged over 20 days on the Si-DLC modified with oxygen plasma. Further explanation for this superior durability of the superhydrophilicity comes from observing the surface morphology evolution due to oxygen plasma treatment: nano-pillar-like structures develop on Si-DLC with the Si weight fraction of 1.24 and 2.66% due to oxygen plasma while no surface structure change is observed on films with other Si fractions.