Even Hot Water Droplets Can Bounce off of a Superhydrophobic Surface*

Drops of scalding water can cause severe burns when it sticks to skin or clothing.  One proposed method to mitigate this problem is to develop a superhydrophobic-coated fabric which would minimize the contact time of the hot drop, and by extension the heat transfer.  Yet, drops that bounce on a superhydrophobic surface when they are warm can stick to the surface if they approach boiling temperatures.  These results are consistent with the idea that evaporated vapor from the drop that condenses on the solid would transition the drop into a Wenzel state. This circumstance provides a new challenge to identify if a material or surface coating exists that could overcome this limitation.  Here, we compare several distinct superhydrophobic surfaces and find that there indeed exists some structures that can repel water even at near boiling temperatures. We explore various parameters for each of the surfaces that might shed insight into why only certain surfaces can overcome the near-boiling bouncing limitation.