Flow of Foams

Foams are probably the simplest forms of matter that exhibit simultaneous elastic, plastic and viscous behavior, i.e., the complex flows characteristic for a wide class of disordered media which also include colloidal suspensions, emulsions, slurries, pastes and granular media. Interest in these materials has always been strong from an applied perspective, but in recent years, numerous new ideas (jamming, force networks, shear transformation zones, soft glassy rheology) and tools (confocal microscopy, tomography, fast video imaging and particle tracking, large scale simulations) have become available to study these materials from a fundamental perspective.

Currently, there are rapid developments on the flow of foams. Experimentally, 2D systems are producing detailed insight into the effects of flow geometry, disorder and strain rate on foam flows and shear bands, and by imaging bubble deformations we now have access to the forces and stresses inside the material. Elementary dissipative relaxations (T1’s) have been studied in great detail. Theoretically, our knowledge of bubble interactions is still advancing, a variety of microscopic models have been proposed (Evolver, Potts, Bubble model), and there is an upsurge in interest in critical aspects of bubble flows.

There are, however, many loose ends and open questions:

What simple microscopic models do describe realistic foam flows best? How do we deal with disorder? What is the role of T1 rearrangements? How important are material properties? How to think about yield stresses and visco-elastic effects? Do ideas on jamming, shear transformation zones and soft glassy rheology help us understand foam flows?

An important goal of this workshop is to shed light on these questions and establish bridges to workers in adjacent fields, in particular by explore connections to the rheology of other disordered media.