The morphological evolution of impact nanodroplets induced by dynamics and intermolecular interactions

Droplet impact on moving substrates is a prevalent phenomenon in grating antifouling, nanoimprint lithography, and inkjet printing. However, how substrate surface properties and dynamic scenarios modify the droplet impact process, especially at the nanoscale, is unclear. Hence, the water nanodroplets impact dynamic solid surfaces is investigated through molecular dynamics simulations in this work. A wide regime of morphologic evolution modes of impinging behaviors, from wetting-spreading (WS) to impact-breakup (IB), have been distinguished by altering normal impact velocities, substrate surface properties, and substrate moving velocities. Four surface properties are normalized by the potential well depth of average Lennard-Jones (LJ) potential energy field (ε_a) from intermolecular interactions and surface topographies. As a boundary condition, five impact equilibrium states are summarized under different ε_a with a wide range of dynamic conditions. We demonstrate that the crucial configuration of droplet bounce is a function of the normal Reynolds number (Re_n) and the tangential Weber number (We_t), which may be expressed as: k₀We_tRe_n + k₁We_t + k₂Re_n + k₃ = 0. This criterion gives a good prediction for the bounce of water nanodroplet after impacting on a substrate with surface properties (ε_a) and dynamic factors coupled. Our findings and results enhance the understanding of the bouncing of impact nanodroplets on dynamic substrates and provide a strategy for grating antifouling, photoresist-drop dispensing in nanoimprint lithography, and anti-icing, which are associated with managing nanodroplet impact behaviors.