Investigation of $q$-dependent dynamical heterogeneity in a colloidal gel by x-ray photon correlation spectroscopy

TL;DR

This study uses X-ray photon correlation spectroscopy to analyze the slow, heterogeneous dynamics of colloidal gels, revealing a non-monotonic fluctuation amplitude dependence on scattering vector and proposing a scaling model.

Contribution

It introduces a novel analysis of $q$-dependent dynamical heterogeneity in colloidal gels using X-ray correlation spectroscopy, with a new scaling argument for fluctuation behavior.

Findings

Dynamical fluctuations are temporally heterogeneous.

Fluctuation amplitude varies non-monotonically with scattering vector $q$.

Proposed a scaling model explaining $q$-dependence in glassy systems.

Abstract

We use time-resolved X-Photon Correlation Spectroscopy to investigate the slow dynamics of colloidal gels made of moderately attractive carbon black particles. We show that the slow dynamics is temporally heterogeneous and quantify its fluctuations by measuring the variance $\chi$ of the instantaneous intensity correlation function. The amplitude of dynamical fluctuations has a non-monotonic dependence on scattering vector $q$, in stark contrast with recent experiments on strongly attractive colloidal gels [Duri and Cipelletti, \textit{Europhys. Lett.} \textbf{76}, 972 (2006)]. We propose a simple scaling argument for the $q$-dependence of fluctuations in glassy systems that rationalizes these findings.