• Journal of the Korean Society for Precision Engineering
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• v.31 no.2
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• pp.171-178
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• 2014

In this study, the apparent contact angle on the hydrophilic/hydrophobic surfaces with micropillars was studied. The previous researches showed that the Wenzel equation and the Cassie-Baxter equation were thermodynamically derived for the rough hydrophilic/hydrophobic surfaces and generally referenced on the field of wetting phenomena. For the verification of both equations, the apparent contact angle on the hydrophilic/hydrophobic surfaces with micro-pillars was measured. In the comparison between the measured and estimated apparent contact angles with the equations, the differences between the apparent contact angles were analyzed. Conclusively, the available range and limitation of theoretical equations were investigated and further researches about the apparent contact angle on the rough surfaces were proposed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.2
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• pp.64-69
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• 2010

We investigated the variation in contact angle of a nano-sized water droplet on a nano stripe-patterned surface using molecular dynamics simulation. By changing the height and width of the stripe pillar, and the gap width of the stripes, we observed the contact angle of water droplet in equilibrium. When the surface energies were 0.1 and 0.3 kcal/mol, the calculated contact angles were in good agreement with the Cassie and Baxter equation. However, when the surface energy is 0.5 kcal/mol, the contact angles are observed to be perturbed along the Cassie and Baxter equation.

• Tribology and Lubricants
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• v.33 no.5
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• pp.202-206
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• 2017

In this study, the hydrophobicity properties for riblet surfaces that replicate shark skin are simulated. Riblet surfaces with surface roughness on riblets are generated numerically based on the measured data of real shark skin. We assumed that a rib on a scale is hemi-elliptical surface. The surface used in the simulation for the calculation of contact angle is composed of 9 scales like checkerboard type with a roughness. The contact angle of a water droplet can be calculated using the Wenzel equation and Cassie-Baxter equation for the generated riblet surfaces. The variation of contact angles with a fractional depth of penetration for the generated shark skin surfaces without and with coatings is demonstrated in the condition of solid-air-water. The results show that the contact angle for the surface without coating decreases with an increase of the fractional depth of penetration more drastically than that for the surface with coating. We compared the experimental and simulated results. It is shown that the measured contact angles of the shark skin template and the shark skin replica are within the simulated results. Therefore the contact angle of water droplet for rough surfaces can be estimated by the developed numerical method in this study.

• Tribology and Lubricants
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• v.35 no.2
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• pp.94-98
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• 2019

The riblet structure like shark skin has been widely studied owing to its drag reduction and anti-fouling properties. In this study we simulated the wettability of an oil droplet on a riblet surface. We developed a numerical analysis method using the Wenzel equation and Cassie-Baxter equation that can estimate the contact angle with a penetrated depth of the droplet on rough surfaces. Riblet surfaces with nine scales composed of five hemi-elliptical ribs are generated numerically. The variation of contact angles with fractional depth of penetration for the generated riblet surfaces with and without coatings is demonstrated in the condition of solid-air-oil and solid-water-oil interfaces. The contact angle for the uncoated surface decreases with increasing fractional depth of penetration more drastically than that for the coated surface. For the effect of surface roughness on the contact angle of the droplet, the oleophilic surface gives lower contact angle when the surface is rougher, whereas the oleoophobic surface gives higher contact angle with higher roughness To verify the analysis results, the wetting angle was measured in the solid-air-oil interface and solid-water-oil interface for the shark-skin template and shark-skin replica. The effects of teflon coating were also evaluated. It is shown that the simulation results cover the experimental ones.