Coalescence or bounce criterion for droplet collision on a superhydrophobic surface

This study investigates the influence of droplet velocity on the collision behavior of equal-sized binary water droplets impacting head-on on a superhydrophobic surface. Using a high-speed camera, the dynamic process of droplet collision process was recorded, and a theoretical model was developed to describe the critical conditions governing post-collision coalescence or bouncing. The model accurately predicts the critical velocity that determines whether droplets coalesce or rebound after collision. Experimental results show that as droplet velocity increases, the probability of coalescence also increases, while larger droplet diameters correspond to lower critical velocities for the coalescence-bouncing transition. During the deformation stage of collision, internal pressure within the droplets may exceed the surface tension threshold, resulting in coalescence. The proposed theoretical model demonstrates strong agreement with experimental observations and can effectively predict droplet behavior at various velocities. This provides a theoretical basis for controlling droplet collision dynamics, with potential applications in droplet manipulation, sensing, and microreactor technologies.