Effects of size ratio on droplet impact dynamics at microstructured surfaces

The dynamic behavior of droplets on superhydrophobic microstructured surfaces plays a crucial role in applications such as self-cleaning, thermal management, and anti-icing. While previous studies have extensively investigated droplet impact dynamics, the effect of the droplet-to-microstructure size ratio (D/S) on rebound behavior remains insufficiently understood. This study systematically examines the influence of D/S on impact dynamics, revealing a transition from inertia-dominated macroscopic effects to adhesion-governed localized interactions. At larger D/S, inertia and surface tension primarily dictate retraction, leading to symmetric rebound. However, as D/S decreases, intensified contact line pinning prolongs contact time and suppresses rebound, fundamentally altering retraction dynamics. A previously unreported transition in droplet retraction is identified, where localized constraints progressively hinder contact line motion, shifting the governing mechanism from inertia-driven to adhesion-controlled behavior. To further elucidate this transition, a theoretical framework is established to characterize the role of D/S in contact line dynamics, linking size-dependent interfacial interactions to droplet mobility. These findings provide new insights into droplet impact physics and serve as a theoretical foundation for optimizing superhydrophobic surfaces in applications such as anti-icing and spray cooling.