A new regime of droplet ejection following the slow deposition of drops onto a near-complete wetting solid substrate is identified in experiments and direct numerical simulations; a coalescence cascade subsequent to pinch-off is also observed for the first time. Results of numerical simulations indicate that the propagation of capillary waves that lead to pinch-off is closely related to the self-similar behaviour observed in the inviscid recoil of droplets, and that motions of the crests and troughs of capillary waves along the interface do not depend on the wettability and surface tension (or Ohnesorge number). The simulations also show that a self-similar theory for universal pinch-off can be used for the time evolution of the pinching neck. However, although good agreement is also found with the double-cone shape of the pinching neck for droplet ejection in drop deposition on a pool of the same liquid, substantial deviations are observed in such a comparison for droplet ejection in rapid drop spreading (including the newly identified regime). This deviation is shown to result from interference by the solid substrate, a rapid downwards acceleration of the top of the drop surface and the rapid spreading process. The experiments also confirm non-monotonic spreading behaviour observed previously only in numerical simulations, and suggest substantial inertial effects on the relation between an apparent contact angle and the dimensionless contact-line speed.

We investigate the cavity formation during the impact of spheres and cylinders into a liquid pool by using a combination of experiments, simulations and theoretical analysis, with particular interest in contact-line pinning and its relation with the subsequent cavity evolution. The flows are simulated by a Navier-Stokes diffuse-interface solver that allows for moving contact lines. On the basis of agreement on experimentally measured quantities such as the position of the pinned contact line and the interface shape, we investigate flow details that are not accessible experimentally, identify the interface regions in the cavity formation and examine the geometric effects of impact objects. We connect wettability, inertia, geometry of the impact object, interface bending and contact-line position with the contact-line pinning by analysing the force balance at a pinned meniscus, and the result compares favourably with those from simulations and experiments. In addition to adjusting the interface bending, the object geometry also has a significant effect on the magnitude of low pressure in the liquid and the occurrence of flow separation. As a result, it is easier for an object with sharp edges to generate a cavity than a smooth object. A theoretical model based on the Rayleigh-Besant equation is developed to provide a quantitative description of the radial expansion of the cavity after the pinning of the contact line. The accuracy of the solution is greatly affected by the geometrical information on the interface connected to the pinned meniscus, showing the dependence of the global cavity dynamics on the local flows around the pinned contact line. Vertical ripple propagation on the cavity wall is found to follow the dispersion relation for the perturbation evolution on a hollow jet.

Zinc (Zn)‐metal anodes are promising candidates for large‐scale, highly safe energy‐storage systems. However, their cycling life is associated with instability issues such as dendritic growth, corrosion, and hydrogen evolution. Introducing an artificial metal interface is expected to help overcome this challenge owing to the optimization of the absorption, nucleation, and growth of Zn2+. In this study, an ultrafast, universal, and cost‐effective superfilling approach is developed to construct a metal artificial interface decorated Zn anode in situ. Most zincophilic metals, including Sn, Cu, and Ag, can be used to construct a homogenous interface without any restrictions on the size, morphology, or curvature of the substrates. With Sn as a proof‐of‐concept demonstration, the as‐obtained Sn@Zn anode is conducive for the homogenous Zn nuclei and 2D diffusion of Zn2+ ions. Symmetric cells with Sn@Zn electrodes can be operated for over 900 h at different current densities. This superior performance contributes to the attractive electrochemical characteristics of both coin and scaled‐up Sn@Zn//β‐MnO2 cells. Given the facile and cost‐effective fabrication and recyclability of the cells, this work enables the efficient design and exploration of Zn anodes for research, industrialization, and commercialization purposes.