Slow relaxation and landscape-driven dynamics in viscous ripening foams

Area of Science:

• Soft Matter Physics
• Rheology
• Materials Science

Background:

• Foams and dense emulsions exhibit complex mechanical behaviors like intermittent dynamics and power-law rheology.
• These behaviors have been traditionally attributed to glassy physics, similar to cytoskeletal mechanics.

Purpose of the Study:

• To investigate the physical origin of anomalous mechanics in simulated wet foams undergoing viscous ripening.
• To differentiate the foam's dynamics from that of glasses.

Main Methods:

• Simulating a wet foam driven by the ripening process.
• Analyzing the balance of forces between the system's potential energy landscape and viscous stress.
• Examining bubble dynamics at varying viscosities.

Main Results:

• Foam dynamics arise from a balance of forces within a self-similar potential energy landscape and viscous stress, distinct from glassy physics.
• At low viscosities, intermittent bubble movement occurs between shallow energy minima. At high viscosities, continuous movement follows a fractal path in configuration space.
• Long-time dynamics and power-law rheology are direct consequences of the energy landscape's self-similar geometry.

Conclusions:

• Viscous ripening foams exhibit anomalous mechanics due to their unique potential energy landscape, not glassy physics.
• Slow recovery after perturbation is attributed to kinetic trapping in high-energy landscape regions.
• Foams follow a biased energy minimization pathway exploring qualitatively different landscape regions than well-annealed glasses.