Ultrafast bounce of particle-laden droplets

Abstract

The rebound of liquid droplets on solid surfaces exhibits behavior reminiscent of elastic spheres, albeit with distinct contact dynamics. While the rapid detachment of droplets from surfaces holds significant relevance for various applications, previous endeavors relying on engineered surfaces can only reduce the contact time to several milliseconds, primarily due to capillary effects dominating droplet bounce. Here, we present ultrafast rebound by designing heterogeneous core-shell droplets encapsulating a particle (DEP), which achieves an unprecedentedly short contact time of 0.3 ms and 0.05 ms with polydimethylsiloxane and glass particles, respectively. This remarkable contact-time reduction is universally applicable to diverse systems, including both water and oil droplets, elastic and rigid particles, super-repellent and superlyophilic surfaces, and is effective across a wide range of impact velocities. Beyond exhibiting liquid-like dynamics, DEP manifests solid-like behavior owing to asynchronized motions between the particle and the droplet, which effectively breaks down the dominance of capillarity. With systematic experimental and analytical studies, we delineate contact times in three bouncing regimes and identify critical conditions governing regime transitions. DEP amalgamates the bouncing dynamics of both solids and liquids, offering a robust and versatile strategy for tailoring contact time to suit diverse applications involving solid-liquid composite systems.