With the emergence of advanced technologies like nanoprinting, the impact dynamics of nanodroplets have attracted growing attention. In practical printing processes, off-center impacts of droplets on curved surfaces are frequently encountered, yet the underlying mechanisms remain insufficiently understood. In this study, molecular dynamics simulations are employed to systematically investigate the off-center impact of nanodroplets on hydrophobic and hydrophilic spheres, with the aim of comprehensively elucidating the impact outcomes. Four outcomes are identified: deposition, bouncing, dripping, and separation. All outcomes are observed on hydrophobic surfaces, whereas bouncing is suppressed on hydrophilic surfaces due to the enhanced solid–liquid adhesion. Based on these outcomes, phase diagrams are constructed for impacts on the hydrophobic and hydrophilic spheres. The separation-dripping boundary shows that the critical Weber number (We) increases with the normalized off-center distance (B) on both hydrophilic and hydrophobic surfaces. Nonetheless, for the boundary between separation and other outcomes, on hydrophobic surfaces, the critical We increases with B, while it in turn decreases with B on hydrophilic surfaces. The observed boundary on hydrophobic surfaces challenges the conventional understanding that increasing B enhances the off-center kinetic energy to promote separation. This is because on hydrophobic surfaces, the head-on part bounces off spheres with significant rotational motion, followed by the occurrence of separation. For this situation, the bouncing kinetic energy drives the separation process, instead of the off-center kinetic energy. Based on different mechanisms of separation, two boundary equations are proposed by using distinct driving kinetic energy, which show good agreement with our simulation results.
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