In this paper, we experimentally and numerically investigated the spreading of impinging droplets of two sizes and different viscosities on nanostructured superhydrophobic surfaces. We show that the spreading characteristics of impinging droplets are highly dependent on the impact velocity and liquid viscosity, but less dependent on the droplet size. The maximum spreading factor, which increases with impact velocity but decreases with liquid viscosity, cannot be well described by the theoretical models developed at a level of scaling analysis in the literature. Based on numerical simulations, we analyze the temporal evolution of all energy terms involved in the dynamics, and demonstrate that the deviation of the theoretical predictions from experimental results is due to the neglect of the residual kinetic energy and improper estimation of the interfacial and viscous dissipation energies in the theoretical models. Published by AIP Publishing.
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