Spatially heterogeneous dynamics in a thermosensitive soft suspension before and after the glass transition

TL;DR

This study investigates the microscopic dynamics and aging of a thermosensitive soft suspension, revealing spatial heterogeneity and non-Gaussian behavior of particle displacements across different states, including glass transition.

Contribution

It demonstrates that non-Gaussian displacement distributions are due to spatially heterogeneous dynamics, characterized by local Gaussian PDFs but global non-Gaussian PDFs, across various states of the suspension.

Findings

Non-Gaussian PDFs with exponential tails are observed above and below the glass transition.

Spatial heterogeneities increase with volume fraction and aging.

Local PDFs remain Gaussian despite global non-Gaussian behavior.

Abstract

The microscopic dynamics and aging of a soft thermosensitive suspension was investigated by looking at the thermal fluctuations of tracers in the suspension. Below and above the glass transition, the dense microgel particles suspension was found to develop an heterogeneous dynamics, featured by a non Gaussian Probability Distribution Function (PDF) of the probes' displacements, with an exponential tail. We show that non Gaussian shapes are a characteristic of the ensemble-averaged PDF, while local PDF remain Gaussian. This shows that the scenario behind the non Gaussian van Hove functions is a spatially heterogeneous dynamics, characterized by a spatial distribution of locally homogeneous dynamical environments through the sample, on the considered time scales. We characterize these statistical distributions of dynamical environments, in the liquid, supercooled, and glass states, and show that it can explain the observed exponential tail of the van Hove functions observed in the concentrated states. The intensity of spatial heterogeneities was found to amplify with increasing volume fraction. In the aging regime, it tends to increase as the glass gets more arrested.