Anomalous dynamics of intruders in a crowded environment of mobile obstacles

TL;DR

This study investigates how small particles move through a crowded, glassy environment of larger particles, revealing a critical size difference that causes anomalous collective transport characterized by logarithmic decay.

Contribution

It uncovers a critical size asymmetry leading to anomalous transport in crowded environments, emphasizing the role of matrix mobility in such dynamics.

Findings

Critical size asymmetry causes anomalous transport.

Logarithmic decay of density autocorrelation functions observed.

Matrix mobility is key to the anomalous behavior.

Abstract

Many natural and industrial processes rely on constrained transport, such as proteins moving through cells, particles confined in nanocomposite materials or gels, individuals in highly dense collec- tives and vehicular traffic conditions. These are examples of motion through crowded environments, in which the host matrix may retain some glass-like dynamics. Here we investigate constrained transport in a colloidal model system, in which dilute small spheres move in a slowly rearranging, glassy matrix of large spheres. Using confocal differential dynamic microscopy and simulations, we discover a critical size asymmetry at which anomalous collective transport of the small particles appears, manifested as a logarithmic decay of the density autocorrelation functions. We demonstrate that the matrix mobility is central for the observed anomalous behaviour. These results, crucially depending on size-induced dynamic asymmetry, are of relevance for a wide range of phenomena ranging from glassy systems to cell biology.