Critical contact angle of a bouncing droplet

Bouncing droplets on solid surfaces is of great significance in diversified applications such as anti-icing and self-cleaning. It is important to establish a unified model to predict whether an impacting droplet can rebound from a surface or not. This work focuses on the rebound dynamic of a droplet impacting a hydrophobic surface via theoretical methods. Based on energy conservation, a new theoretical model to predict the rebound behavior of an impacting droplet is established. For an ideal surface, the contact angle hysteresis Δθ can be ignored and the rebound condition is θ ≥ θ_c,i, where θ is the equilibrium contact angle and θ_c,i is the critical rebounding contact angle (CRCA) of an ideal surface. For a real surface, Δθ is considered and the rebound condition is θ_r ≥ θ_c,r, where θ_r is the receding contact angle and θ_c,r is CRCA of a real surface. Especially, when Δθ is not large enough, the rebound condition for a real surface can be expressed as θ_r ≥ θ_c,i. This work is the first to establish the theoretical model considering both the energy dissipation throughout the impact process and the contact angle hysteresis, which shows a higher consistency with the previous works. 
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