Ultra-long range correlations of the dynamics of jammed soft matter

TL;DR

This study reveals that deeply jammed soft materials exhibit ultra-long range spatial correlations in their dynamics, extending system-wide, which contrasts with shorter correlations in supercooled fluids, and relates to the material's elasticity type.

Contribution

It demonstrates that jammed soft matter systems have system-size scale correlations linked to their elastic properties, using space-resolved dynamic light scattering.

Findings

Correlations extend up to the system size in jammed soft materials.

Shorter correlations are observed in supercooled fluids.

Elasticity type influences the range of dynamic correlations.

Abstract

We use Photon Correlation Imaging, a recently introduced space-resolved dynamic light scattering method, to investigate the spatial correlation of the dynamics of a variety of jammed and glassy soft materials. Strikingly, we find that in deeply jammed soft materials spatial correlations of the dynamics are quite generally ultra-long ranged, extending up to the system size, orders of magnitude larger than any relevant structural length scale, such as the particle size, or the mesh size for colloidal gel systems. This has to be contrasted with the case of molecular, colloidal and granular ``supercooled'' fluids, where spatial correlations of the dynamics extend over a few particles at most. Our findings suggest that ultra long range spatial correlations in the dynamics of a system are directly related to the origin of elasticity. While solid-like systems with entropic elasticity exhibit very moderate correlations, systems with enthalpic elasticity exhibit ultra-long range correlations due to the effective transmission of strains throughout the contact network.