Energy-based modeling of micro- and nano-droplet jumping upon coalescence on superhydrophobic surfaces.

Existing energy-based models on coalescence-induced droplet jumping on superhydrophobic surfaces often assume that the viscously dissipated energy is proportional to the Ohnesorge (Oh) number (linear form). Based on the numerical results by two different methods, we found that the energy dissipation for droplet coalescence follows a power law form. What is more, the energy dissipation at the time of droplet jumping was found to be larger than that of droplet coalescence. Besides, existing energy-based models assume a fixed portion of translational kinetic energy (KE) within the droplet's total KE, whereas it actually varies with the Oh number from our simulations. Incorporating a special form of energy dissipation and an Oh-dependent portion of translational KE, we obtained an improved model that can predict the jumping velocity of the coalesced droplet of tens of nanometer- to micrometer-size on nonwetting surfaces much more accurately than the existing energy-based models. Finally, we extended the model for superhydrophobic surfaces with finite adhesion and demonstrated its capability through extensive comparisons with relevant experimental and numerical results. [ABSTRACT FROM AUTHOR]