An experimental study of bouncing Leidenfrost drops: Comparison between Newtonian and viscoelastic liquids

The effect of polymer additives on the dynamic Leidenfrost phenomenon (rebound of liquid drops impacting on very hot walls, where a thin vapour cushion separates the liquid from the surface) is studied experimentally by high-speed imaging. Drops of a dilute solution (200 ppm) of Polyethylene Oxide (PEO), with equilibrium diameters of 2.66 and 3.32 mm, were compared with drops of pure water (diameters of 2.76 and 3.49 mm) during the impact on an aluminium surface at a temperature of 400 degrees C and impact Weber numbers between 7 and 160. The additive causes a slight reduction of the maximum spreading diameter and of the retraction velocity of the drop after impact and, within a certain range of Weber numbers, enhances significantly the maximum height of the drop center of mass during rebound. These results, obtained for a non-wetting case, are different from those previously obtained for impacts on dry surfaces, where polymer additives hardly change the maximum spreading diameter but reduce the retraction velocity of nearly one order of magnitude and completely suppress drop rebound. (C) 2008 Elsevier Ltd. All rights reserved.