The emergence of soft-glassy dynamics in foams

Many seemingly simple materials such as foams and emulsions exhibit complex physical and rheological properties whose physical origins have largely defied understanding. Soft-sphere models have proven very useful in understanding various mechanical and rheological properties of soft-glassy systems like foams and emulsions. Previous experimental studies, however, have failed to capture various complex phenomena such as intermittent dynamics, power-law rheology, super-diffusive bubble motion and others in their entirety. We simulate a viscously damped soft-sphere bubble model, subjected to Ostwald ripening, over a wide range of viscosity. The results capture the various contrasting phenomena observed in previous experimental studies. Systems with higher effective viscosity/damping produce less intermittent motion with configuration structures farther away from jamming. Conversely, systems without little to no viscosity/damping display highly intermittent dynamics, heavy-tailed bubble displacement distribution functions and power-law rheology. Lastly, this model produces interesting damping correlated aging dynamics for perturbed systems, with time scales for recovery to steady state vanishing in the quasi-static limit (zero viscosity) indicating little to no self organization in these systems.