Localization dynamics of fluids in random confinement

TL;DR

This study explores how fluids behave in random confined environments, revealing a transition from delocalized to localized motion influenced by obstacle density, with experimental and simulation evidence showing a smooth transition rather than a sharp one.

Contribution

It provides new insights into the localization dynamics of fluids in random matrices, combining experiments and simulations to show a rounded transition in soft interaction systems.

Findings

Delocalized tracer particles at low obstacle densities.

Localized trapping of tracers at high obstacle densities.

Smooth transition from delocalization to localization in soft interaction systems.

Abstract

The dynamics of two-dimensional fluids confined within a random matrix of obstacles is investigated using both colloidal model experiments and molecular dynamics simulations. By varying fluid and matrix area fractions in the experiment, we find delocalized tracer particle dynamics at small matrix area fractions and localized motion of the tracers at high matrix area fractions. In the delocalized region, the dynamics is subdiffusive at intermediate times, and diffusive at long times, while in the localized regime, trapping in finite pockets of the matrix is observed. These observations are found to agree with the simulation of an ideal gas confined in a weakly correlated matrix. Our results show that Lorentz gas systems with soft interactions are exhibiting a smoothening of the critical dynamics and consequently a rounded delocalization-to-localization transition.