The fluid dynamics of foams

Liquid foam is an example of soft matter (or a complex fluid) with a very well-defined structure, first clearly described by Joseph Plateau in the 19th century. Current research addresses many aspects of the fluid dynamics of this system. How is liquid transported through it in response to a pressure gradient or gravity? How does it respond to stress, particularly above the yield stress? What is the nature of the local fluid flow in the Plateau borders and their junctions? Simple first-order answers to many such questions exist but ongoing experiments continue to challenge our understanding.