Dynamic heterogeneities and non-Gaussian behavior in two-dimensional randomly confined colloidal fluids

TL;DR

This study investigates how two-dimensional colloidal fluids confined by a disordered matrix exhibit heterogeneous and non-Gaussian dynamics, influenced by soft interactions and matrix density, with insights supported by experiments and molecular dynamics simulations.

Contribution

It demonstrates the impact of soft interactions on heterogeneity and non-Gaussian behavior in confined colloidal fluids, expanding understanding beyond traditional Lorentz gas models.

Findings

Heterogeneous dynamics increase with matrix density.

Soft interactions enhance non-Gaussian fluctuations.

Simulations replicate experimental heterogeneity patterns.

Abstract

A binary mixture of super-paramagnetic colloidal particles is confined between glass plates such that the large particles become fixed and provide a two-dimensional disordered matrix for the still mobile small particles, which form a fluid. By varying fluid and matrix area fractions and tuning the interactions between the super-paramagnetic particles via an external magnetic field, different regions of the state diagram are explored. The mobile particles exhibit delocalized dynamics at small matrix area fractions and localised motion at high matrix area fractions, and the localization transition is rounded by the soft interactions [T. O. E. Skinner et al, Phys. Rev. Lett. {\bf 111}, 128301 (2013)]. Expanding on previous work, we find the dynamics of the tracers to be strongly heterogeneous and show that molecular dynamics simulations of an ideal gas confined in a fixed matrix exhibit similar behavior. The simulations show how these soft interactions make the dynamics more heterogenous compared to the disordered Lorentz gas and lead to strong non-Gaussian fluctuations.