Liquid Drops Impacting Superamphiphobic Coatings

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• 作者：Xu Deng ; Frank Schellenberger ; Periklis Papadopoulos ; Doris Vollmer ; Hans-J眉rgen Butt
• 刊名：Langmuir
• 出版年：2013
• 出版时间：June 25, 2013
• 年：2013
• 卷：29
• 期：25
• 页码：7847-7856
• 全文大小：522K
• 年卷期：v.29,no.25(June 25, 2013)
• ISSN：1520-5827

文摘

The dynamics of liquid drops impacting superamphiphobic coatings is studied by high-speed video microscopy. Superamphiphobic coatings repel water and oils. The coating consists of a fractal-like hydrophobized silica network. Mixtures of ethanol鈥搘ater and glycerin鈥搘ater are chosen to investigate the influence of interfacial tension and viscosity on spreading and retraction dynamics. Drop spreading is dominated by inertia. At low impact velocity, the drops completely rebound. However, the contact time increases with impact velocity, whereas the restitution coefficient decreases. We suggest that the drop temporarily impales the superamphiphobic coating, although the drop completely rebounds. From an estimate of the pressure, it can be concluded that impalement is dominated by depinning rather than sagging. With increasing velocity, the drops partially pin, and an increasing amount of liquid remains on the coating. A time-resolved study of the retraction dynamics reveals two well-separated phases: a fast inertia-dominated phase followed by a slow decrease of the contact diameter of the drop. The crossover occurs when the diameter of the retracting drop matches the diameter of the drop before impact. We suggest that the depth of impalement increases with impact velocity, where impalement is confined to the initial impact zone of the drop. If the drop partially pins on the coating, the depth of impalement exceeds a depth, preventing the whole drop from being removed during the retraction phase.