Phase diagram and boundary of impact outcomes

This study investigates the outcomes of droplet impact under varying impact velocities (Weber numbers) and surface wettability, using experimental methods, with a particular focus on the boundaries between these outcomes. Three primary outcomes were identified at lower Weber numbers (We ≤ 100): deposition, partial rebound, and complete rebound. Discrepancies were observed between existing boundary models for rebound (partial and complete) and deposition, and the actual experimental results. To address this, a new model was developed based on the “water spring model” proposed by Balance et al., incorporating the effects of contact line dissipation and adhesion forces. This model showed improved accuracy in predicting these outcomes. At higher Weber numbers (We > 100) and contact angles (θ > 100°), two main outcomes, receding breakup and prompt splash, were observed. By comparing the instability stresses driving these outcomes, a novel predictive boundary for receding breakup and prompt splash was proposed. This model's accuracy was validated through experimental data from phase diagrams. This research offers new insights into understanding droplet impact behavior under different surface wettability conditions.