Joo Hyun Moon

Wetting Characteristic of Single Droplet Impinging on Hole-Patterned Texture Surfaces

Abstract This study presents the dynamic wetting characteristics of an impact droplet on hole-patterned textured surfaces. The flatsurfaces were manufactured by a drilling machine to generate the micro-order holes, leading to make the surface hydropho-bic. Other flat surfaces were fabricated by the anodizing technique to make hydrophilic texture surfaces with a nanometerorder. For hydrophilic and hydrophobic textured surfaces with similar texture area fractions, the impinging droplet experi-ments were conducted and compared with flat surface cases. As results, an anodized textured surface decreases apparent equi-librium contact angle and increases contact diameters, because of increase in contact area and surface energy. This isattributed to more penetration inside holes from larger capillary pressure on nanometer-order holes. On the other hand, tem-poral evolution of the contact diameter is smaller for the hydrophobic textured surface from less penetration on the micro-order holes. 기호설명

Dynamic Characteristics of Droplet Impinging on Multi-layer Texture Surfaces

Abstract This study presents the dynamic characteristics of an impinging droplet on hydrophobic and hydrophilic surfaces with var-ious texture area fractions. The flat surface was fabricated by using the drilling technique to make micro-meter hole-patternedsurfaces, which shows hydrophobic textured surfaces. Moreover, the hydrophilic textured surfaces were manufactured byanodizing technique on the micro-meter hole-patterned surfaces to generate multi-layer surfaces. Impinging droplet experi-ments were conducted for various hole-patterned surfaces, with changing impact velocity and texture area fractions. It isobserved that an anodizing technique increases wettability by decrease in hole diameter on the textured surfaces. However,micro-drilled surfaces decreases wettability because the hole diameter was so large that air can be trapped under the holes.In addition, the maximum spreading diameter decreases with the texture area fraction for the micro-drilled surfaces becauseof decrease in wettability.

Dynamics of a non-Newtonian Droplet Impact on a Micro-Textured Surface

This study investigated the impact dynamics of single Newtonian and non-Newtonian droplets impinging on a textured aluminum (Al 6061) surface fabricated by using a -computer numerical control ( -CNC) machine. DI-water was chosen as a Newtonian fluid, while 0.5 wt.% Xanthan Gum (Sigma-Aldrich) solution was selected for a non-Newtonian fluid. The non-Newtonian droplets show a shear-thinning characteristics, higher zero shear viscosity than DI-water. The textured surfaces are composed of micro-holes (diameter: 250 m, depth: 500 m) with equivalent pitches, without showing very similar apparent equilibrium contact angles of both Newtonian and non-Newtonian droplets. We measured spreading and receding diameters from images captured by a high-speed camera of 10,000 fps (HG-LE, Redlake). 6.4 l droplets impinged on the textured surfaces ( s=0.28) with an impact velocity of 1.213 m/s. The normalized maximum spreading diameter (D*) of a non-Newtonian impinging droplet is the smaller, and the corresponding lamella thickness is the larger because of the increase in viscosity dissipation. For a non-Newtonian fluid, the receding is also slower than that of Newtonian fluid at the relaxation phase because of the viscosity effect. t = 0.5 ms