Viscoelastic coarsening of quasi-2D foam

TL;DR

This paper investigates how viscoelasticity in the continuous phase of foams affects their coarsening process, revealing slowed bubble growth and heterogeneous structures due to altered phase redistribution and mechanical properties.

Contribution

It provides the first detailed analysis of coarsening in viscoelastic foams, highlighting the impact of viscoelasticity on foam stability and structure.

Findings

Bubble size evolution is significantly slowed.

Foam structure becomes spatially heterogeneous.

Absence of continuous phase redistribution is key.

Abstract

Foams are unstable jammed materials. They evolve over timescales comparable to their "time of use", which makes the study of their destabilisation mechanisms crucial for applications. In practice, many foams are made from viscoelastic fluids, which are observed to prolong their lifetimes. Despite their importance we lack understanding of the coarsening mechanism in such systems. We probe the effect of continuous phase viscoelasticity on foam coarsening with foamed emulsions. We show that bubble size evolution is strongly slowed down and foam structure hugely impacted. The main mechanisms responsible are the absence of continuous phase redistribution and a non-trivial link between foam structure and mechanical properties. These combine to give spatially heterogeneous coarsening. Beyond their importance in the design of foamy materials, the results give a macroscopic vision of phase separation in a viscoelastic medium.