Reducing the contact time of bouncing droplets on superhydrophobic surfaces: Foundations, strategies and applications

The growing demands for superhydrophobic materials in real-world applications, such as anti-icing, heat management, and energy harvesting, cannot be met by solely considering static/quasi-static non-wettability. Instead, dynamic non-wettability featuring minimized duration from the landing of droplet on surfaces to its complete rebound is becoming more important for the applications of superhydrophobic surfaces. For this purpose, a large number of strategies have been developed to reduce contact duration of droplets impacting on surfaces in recent years. In this review, we systematically summarized the research progress in reducing the contact time of impacting droplets on superhydrophobic surface. We first introduce the theory related to droplet impact, including the inertia-capillarity scaled contact time model and the droplet spreading/retraction dynamics. The reported strategies to reduce the contact time are then discussed and classified into four categories: designing macrotextured surfaces, tunning micro/nano-scaled surface structures, regulations of substrate material/coating, and exerting external physical fields. We analyze the advantages and disadvantages of these strategies and compare their enhanced shedding efficiency. Furthermore, we present representative applications of superhydrophobic surfaces with reduced contact time, and give our perspective on the challenges and opportunities in this field.