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Ngo, Chi-Vinh,Chun, Doo-Man Elsevier 2018 CIRP annals ... manufacturing technology Vol.67 No.1
<P><B>Abstract</B></P> <P>Sapphire is a widely used hard transparent material for optics and protective windows, and a superhydrophobic coating on sapphire can prevent contamination by self-cleaning. However, the coating can be easily degraded according to time and heat. In this research, transparent superhydrophobic sapphire surfaces were fabricated via laser surface ablation, without coating, for good stability and heat resistance. The laser ablated surface showed hydrophilic initially, but the wettability transition to superhydrophobic was achieved after an additional simple heat treatment. Contact angle and transmittance were measured to confirm the superhydrophobicity and transparency, and surface analysis was performed to explain the wetting mechanism.</P>
Ngo, Chi-Vinh,Chun, Doo-Man Elsevier BV * North-Holland 2018 Applied Surface Science Vol.435 No.-
<P><B>Abstract</B></P> <P>Recently, controlling the wettability of a metallic surface so that it is either superhydrophobic or superhydrophilic has become important for many applications. However, conventional techniques require long fabrication times or involve toxic chemicals. Herein, through a combination of pulse laser ablation and simple post-processing, the surface of aluminum was controlled to either superhydrophobic or superhydrophilic in a short time of only a few hours. In this study, grid patterns were first fabricated on aluminum using a nanosecond pulsed laser, and then additional post-processing without any chemicals was used. Under heat treatment, the surface became superhydrophobic with a contact angle (CA) greater than 150° and a sliding angle (SA) lower than 10°. Conversely, when immersed in boiling water, the surface became superhydrophilic with a low contact angle. The mechanism for wettability change was also explained. The surfaces, obtained in a short time with environmentally friendly fabrication and without the use of toxic chemicals, could potentially be applied in various industry and manufacturing applications such as self-cleaning, anti-icing, and biomedical devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Superhydrophilic/superhydrophobic Al surfaces were made by laser ablation and simple post process. </LI> <LI> Laser-ablated Al surface became superhydrophobic using heat treatment. </LI> <LI> Laser-ablated Al surface became superhydrophilic using boiling water treatment. </LI> <LI> Mechanism of wettability change to superhydrophobic/superhydrophilic was explained. </LI> <LI> The performances of superhydrophobic and superhydrophilic Al were demonstrated. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Ngo, Chi-Vinh,Chun, Doo-Man Elsevier BV * North-Holland 2017 Applied Surface Science Vol.409 No.-
<P><B>Abstract</B></P> <P>Recently, the fabrication of superhydrophobic metallic surfaces by means of pulsed laser texturing has been developed. After laser texturing, samples are typically chemically coated or aged in ambient air for a relatively long time of several weeks to achieve superhydrophobicity. To accelerate the wettability transition from hydrophilicity to superhydrophobicity without the use of additional chemical treatment, a simple annealing post process has been developed. In the present work, grid patterns were first fabricated on stainless steel by a nanosecond pulsed laser, then an additional low-temperature annealing post process at 100°C was applied. The effect of 100–500μm step size of the textured grid upon the wettability transition time was also investigated. The proposed post process reduced the transition time from a couple of months to within several hours. All samples showed superhydrophobicity with contact angles greater than 160° and sliding angles smaller than 10° except samples with 500μm step size, and could be applied in several potential applications such as self-cleaning and control of water adhesion.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Superhydrophobic surface on SUS304 was fabricated by laser texturing and annealing. </LI> <LI> Wettability transition was done within 4h only with low temperature annealing. </LI> <LI> The effect of grid pattern size upon the wettability change was studied. </LI> <LI> The effect of water droplet contact during wettability change was investigated. </LI> <LI> The mechanism and applications of superhydrophobic surface were proposed. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Transparency and Superhydrophobicity of Cone-Shaped Micropillar Array Textured Polydimethylsiloxane
Chi-Vinh Ngo,Gaasuren Davaasuren,오현석,천두만 한국정밀공학회 2015 International Journal of Precision Engineering and Vol.16 No.7
Transparent superhydrophobic surfaces have great potential for application to self-cleaning transparent windows. We suggest a fabrication method that combines laser beam machining and polymer casting. A UV nanosecond pulsed laser was used to machine arrays of holes into molds composed of 6061 aluminum alloy. Then, polydimethylsiloxane was cast into the laser-machined molds. To study the effects of the array geometry on superhydrophobicity and transparency, a series of micropillar arrays with different step sizes were fabricated. As a result, the critical step size at which the surfaces changed from hydrophobic to superhydrophobic was found to be approximately 80 μm. Cone-shaped micropillar arrays with 80 μm step size showed 175° maximum water droplet contact angle and were highly transparent throughout the 300-1000 nm spectral region. Sliding angle was observed to confirm the surfaces’ self-cleaning ability. This work opens up the possibility of mass production of superhydrophobic, transparent, self-cleaning surfaces.
Chun, Doo-Man,Ngo, Chi-Vinh,Lee, Kyong-Min Elsevier 2016 CIRP annals ... manufacturing technology Vol.65 No.1
<P><B>Abstract</B></P> <P>Recently, cost-effective nanosecond laser texturing has been used for the fabrication of superhydrophobic surface on metals such as copper and brass. However, the wettability change from hydrophilicity to superhydrophobicity took a relatively long time from several days to several months since the textured surface was exposed to ambient conditions. To reduce the time required for wettability changes for industrial applications, a facile post process was introduced. This paper demonstrates fast wettability change of a nanosecond laser textured copper surface from hydrophilic to superhydrophobic using additional low-temperature annealing (100°C). Surface characteristics were evaluated to explain the underlying mechanism.</P>