Impact of compound drops

Drop interaction with solid surfaces upon impact has been attracting a growing attention, focusing more and more on “complex” surfaces and “complex” drops. Recently, there is a clear emerging trend, related to the investigation of compound drop impacts. By studying the dynamics of compound drops consisting of immiscible liquids, we identified the mechanism of self-lubrication of water-in-oil compound drops impacting on a solid surface. The presence of an oil shell encapsulating a core water drop acts as a lubricating layer promoting water rebound even on a hydrophilic substrate, on which water deposition is typically expected. We define the mechanisms and the conditions that lead to deposition or rebound of the inner water drop, which can be useful to define guidelines for processes requiring liquid deposition, e.g. for 3D printing or liquid separation.