The macroscopic pancake bounce

TL;DR

This study demonstrates that the pancake bounce phenomenon of water droplets on structured surfaces can be scaled up to macroscopic levels using a bed of nails and a water balloon, confirming the underlying mechanisms and enabling force measurement.

Contribution

The paper introduces a macroscopic model of pancake bouncing, validating its scalability and providing a simple, accessible way to study droplet-surface interactions.

Findings

Pancake bounce features are reproduced at larger scales.

The Weber number dependence is confirmed in the macroscopic model.

Force exerted during bounce is measurable in the scaled experiment.

Abstract

We demonstrate that the so-called pancake bounce of millimetric water droplets on surfaces patterned with hydrophobic posts [Nat. Phys. 10, 515 (2014)] 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.