On a tweezer for droplets

Authors: John W. M. Bush, François Peaudecerf, Manu Prakash, David Quéré

Link: https://www.sciencedirect.com/science/article/abs/pii/S0001868610000047?via%3Dihub

DOI: https://doi.org/10.1016/j.cis.2010.01.002

Abstract: We describe the physics behind a peculiar feeding mechanism of a certain class of shorebirds, in which they transport their prey in droplets from their beak tips mouthwards. The subtle interplay between the drop and the beak's tweezering motion allows the birds to defy gravity through driving the drop upwards. This mechanism provides a novel example of dynamic boundary-driven drop motion, and suggests how to design tweezers for drops, able to trap and to move small amounts of liquid.

Additional Information:

In physics, ratchets are mechanisms that generate symmetry breaking (due to physical principles) from periodic energy landscape (or motion). A lot of them have been discovered, from a brownian ratchet to an optical ratchet. Here we describe a "capillary ratchet" generated by an asymmetry in contact-angle hysteresis leading to unidirectional droplet propulsion. Sometimes asymmetries can be so mind-bending.