Elastically driven, intermittent microscopic dynamics in soft solids

TL;DR

This study uses 3D simulations to show that elastic fluctuations in soft solids cause intermittent, faster-than-exponential microscopic dynamics, influencing aging and mechanical response.

Contribution

It reveals that elastic recovery and thermal fluctuations govern aging dynamics, highlighting the role of elastic fluctuations in intermittent microscopic behavior.

Findings

Elastic fluctuations cause faster-than-exponential dynamics.

Intermittent stress relaxation is driven by elastic correlations.

Weak thermal fluctuations allow frozen-in stress heterogeneities to relax elastically.

Abstract

Soft solids with tunable mechanical response are at the core of new material technologies, but a crucial limit for applications is their progressive aging over time, which dramatically affects their functionalities. The generally accepted paradigm is that such aging is gradual and its origin is in slower than exponential microscopic dynamics, akin to the ones in supercooled liquids or glasses. Nevertheless, time- and space-resolved measurements have provided contrasting evidence: dynamics faster than exponential, intermittency, and abrupt structural changes. Here we use 3D computer simulations of a microscopic model to reveal that the timescales governing stress relaxation respectively through thermal fluctuations and elastic recovery are key for the aging dynamics. When thermal fluctuations are too weak, stress heterogeneities frozen-in upon solidification can still partially relax through elastically driven fluctuations. Such fluctuations are intermittent, because of strong correlations that persist over the timescale of experiments or simulations, leading to faster than exponential dynamics.