Moving in a mobile crowded environment: anomalous dynamics beyond the Lorentz gas model

Marco Laurati (University of Guanajuato, Mexico)

Many natural and industrial processes rely on constrained transport, such as proteins moving through cells, particles confined in nanocomposite materials and gels and individuals in highly dense groups of humans and animals or vehicular traffic conditions. These are examples of motion through crowded environments, in which the host matrix may retain some slow, glass-like dynamics. In this work we investigated constrained transport in a slowly rearranging environment using binary colloids as model system, in which the dilute small spheres act as intruders and the large spheres form the mobile matrix, generalizing the work of Lorentz on a dilute gas of intruders in an immobile matrix. Using confocal differential dynamic microscopy to resolve the small particles' dynamics, we discover a critical size asymmetry at which anomalous collective transport appears, manifested as a logarithmic decay of the density autocorrelation functions. Numerical simulations elucidate the crucial role played by the host mobility, an aspect which has not been previously considered. We demonstrate that the continuous creation and disruption of channels within the matrix is central for the observed anomalous behaviour. These results, crucially depending on the presence of size-induced dynamic asymmetry, are of relevance for a wide range of phenomena ranging from glassy systems to cell biology.

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