Localization Dynamics of Fluids in Random Confinement

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.

Dimensional study of the dynamical arrest in a random Lorentz gas

“…In the RLG, a spherical particle of radius σ (the tracer) elastically bounces off Poisson-distributed point obstacles (scatterers). When scatterers are sparse, the tracer motion is diffusive after just a few collisions [6], but upon increasing the number density of obstacles, ρ, the tracer first develops an increasingly long subdiffusive regime and then becomes fully localized beyond a finite ρ p [7][8][9]. Interestingly, the onset of dynamical arrest in the RLG can be mapped onto the void percolation transition for overlapping, Poisson-distributed spheres (as can be seen by exchanging the tracer's size with the scatterers'), which provides a static interpretation for the phenomenon.…”

Splitting of the Universality Class of Anomalous Transport in Crowded Media

“…Besides being a testing ground of kinetic theory [2], the Lorentz model has found a fertile soil in many applications, for example, electrical conductivity due to impurity scattering [3], hydrogen storage in hierarchically structured porous materials [4], molecular sieving [5,6], flow in porous media [7,8], and also in connection to oil recovery [9]. A striking prediction is the emergence of subdiffusive motion, which generically occurs in the crowded world of biological cells [10][11][12][13][14].…”

“…For example, if the colloidal realization of the Lorentz model by Skinner et al [8] could be done in d ¼ 3, one expects that hydrodynamic effects due to thin lubrication layers dominate transport through the narrowest channels. Similarly, in the complementary molecular dynamics simulations [46], the percolation threshold is set by the energy of the tracer such that the narrow channels are the ones where the energy barely suffices to pass the barriers.…”

Transport and selective chaining of bidisperse particles in a travelling wave potential

“…The selective chaining process can be used to generate remotely controllable colloidal channels, confining the flow of smaller magnetic particles [30], which presents a mesoscopic model system for transport in a microfluidic medium. Furthermore, of interest is the behaviour of the system at higher densities and in particular how different relative fractions of particles affect transport characteristics.…”