Ricocheting Droplets Moving on Super‐Repellent Surfaces. Issue 21 (12th September 2019) - Pan, Shuaijun
Abstract: Droplet bouncing on repellent solid surfaces (e.g., the lotus leaf effect) is a common phenomenon that has aroused interest in various fields. However, the scenario of a droplet bouncing off another droplet (either identical or distinct chemical composition) while moving on a solid material (i.e., ricocheting droplets, droplet billiards) is scarcely investigated, despite it having fundamental implications in applications including self‐cleaning, fluid transport, and heat and mass transfer. Here, the dynamics of bouncing collisions between liquid droplets are investigated using a friction‐free platform that ensures ultrahigh locomotion for a wide range of probing liquids. A general prediction on bouncing droplet–droplet contact time is elucidated and bouncing droplet–droplet collision is demonstrated to be an extreme case of droplet bouncing on surfaces. Moreover, the maximum deformation and contact time are highly dependent on the position where the collision occurs (i.e., head‐on or off‐center collisions), which can now be predicted using parameters (i.e., effective velocity, effective diameter) through the concept of an effective interaction region. The results have potential applications in fields ranging from microfluidics to repellent coatings. Abstract : Droplets colliding and ricocheting on super‐repellent surfaces display dynamics consistent with droplet–surface collisions, but with tunable dynamics between bouncing droplets via control over the angle of incidence. Parameters introduced using the concept of an effective interaction region allow for a universal description and prediction of droplet bouncing dynamics, with implications for wetting characteristics of next‐generation surfaces.