気泡トラップによるマイクロチャネル内スリップ流形成過程の可視化

抄録

Processes of the air entrapment in microstructures fabricated on walls of rectangular microchannels were visualized by a high-speed camera. Effects of the geometry of the microstructures on the formation and the shape of the liquid-gas interface in the microstructures were investigated with four channels having the same dimensions but different microstructure geometries at Re = 1. The microchannels were made of stainless steel and acrylic, and the microstructures were hydrophobized by triazinethiol. Water-ethanol mixtures with different mixing rate (ranged from 100:0 to 0:100) were employed as the test liquids, thereby effects of the wettability on the liquid-gas interface formation process was able to be investigated as well. Consequently, the following four types of the interface behaviors were observed: (a) complete air entrapment with concave liquid-gas interfaces in the microstructures, (b) almost entire part of the microstructures are filled with air with convex liquid-gas interfaces, (c) whole wall is wetted, while a little portion of air is left in the microstructures (the air phase is surrounded by the liquid phase), and (d) the microstructures are completely filled with the liquid phase. Type (a) was achieved only when the advancing contact angle was larger than the angle of the final shape of the liquid-gas interfaces, whereas Type (b), Type (c), and Type (d) showed dependencies on both the geometry of the microstructures and the wettability. The results will qualitatively help a strategy for the fabrication of the microstructures to obtain more proper shape of the liquid-gas interface for maximizing the slip length and the resulting drag reduction effect in microchannels.