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

Abstract

The microscopic dynamics and aging of a soft thermosensitive suspension were investigated by looking at the thermal fluctuations of tracers in the suspension. Below and above the glass transition the dense microgel particle suspension was found to develop heterogeneous dynamics, characterized 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 PDFs 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 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.