Fig. 2. Adhesion of water on hot repellent materials.
(A) Sketch of the experiment: A water drop with volume Ω and contact radius r is placed on a substrate brought to a temperature T and tilted until the drop departs. At departure (tilting angle α), contact angles at the drop edges are the receding and advancing angles θr and θa, respectively. (B) Roll-off angle α as a function of temperature T for Ω = 3.9 μl (blue data), Ω = 5.4 μl (red data), and Ω = 9.2 μl (green data). Error bars show the standard deviation for a minimum of five measurements. (C) Contact angle hysteresis Δcosθ = cosθr – cosθa deduced from Furmidge’s equation: Water adhesion is nonmonotonic as a function of T, and it becomes nonmeasurable above ~130°C.