Impact Dynamics of Water Droplets on Hydrophobic Spheres: Molecular-Scale Insights for Electronic Thermal Interfaces

This study investigates the normal impact force generated during the collision of water droplets with hydrophobic spherical substrates, aiming to understand the coupled effects of curvature, velocity, and wettability on interfacial momentum transfer. Using molecular dynamics simulations, we systematically analyze the evolution of force under varying radius ratios, impact velocities, and contact angles. Results show that increased curvature (larger R^*) enhances force transfer due to more effective momentum redistribution. Higher velocities result in sharper force peaks, while the effect of wettability exhibits a nonmonotonic trend, with intermediate contact angles yielding the strongest force response. A scaling model is proposed to quantify the peak impact force, incorporating geometric, inertial, and adhesive factors. The derived relation, F_peak ∝ (R^*)^0.58v^1.89(1 - λ cos θ), matches well with simulation data (R² > 0.9). This work provides both physical insight and predictive capability for the design of curved liquid-solid interfaces in thermal and electronic applications.