Explosive behavior during binary-droplet impact on superheated substrates

Abstract Droplet impact on superheated smooth solids has attracted enormous attention since Leidenfrost reported the eponymous phenomenon over 250 years ago. The related literature has almost exclusively focused on pure liquids, which maintain their volume integrity even under disruptive nucleate boiling (characterized by the vigorous ejection of tiny droplets from the parent droplet). This study provides evidence of the existence of a new regime – termed explosive boiling – for impact of binary (composed of two miscible liquids) droplets on superheated substrates at temperatures between the respective Leidenfrost temperatures of the two liquid constituents. The distinct characteristic of this regime is a violent breakup of the parent droplet, and is observed only for the lower concentrations of the more volatile component of the mixture. These concentrations seem to maximize the instability of the vapor layer between the droplet and the wall. We explore this previously-unseen behavior, considering the different volatilities of the two liquid constituents and their relative volume ratios in the impacting droplet.