The macroscopic pancake bounce

Abstract

We demonstrate that the so-called pancake bounce of millimetric water droplets on surfaces patterned with hydrophobic posts (Liu et al 2014 Nat. Phys. 10 515) can be reproduced on larger scales. In our experiment, a bed of nails plays the role of the structured surface and a water balloon models the water droplet. The macroscopic version largely reproduces the features of the microscopic experiment, including the Weber number dependence and the reduced contact time for pancake bouncing. The scalability of the experiment confirms the mechanisms of pancake bouncing, and allows us to measure the force exerted on the surface during the bounce. The experiment is simple and inexpensive and is an example where front-line research is accessible to student projects.