Super-Arrhenius diffusion in a binary colloidal mixture at low volume fraction: an effect of depletion interaction due to an asymmetric barrier

TL;DR

This study uses molecular dynamics simulations to explore how asymmetric external barriers induce super-Arrhenius diffusion in larger particles of a low-density binary colloidal mixture, revealing a crossover in diffusion behavior.

Contribution

It demonstrates that asymmetry in external potential barriers causes a transition from sub-Arrhenius to super-Arrhenius diffusion for larger particles at low volume fractions, a novel insight.

Findings

Larger particles exhibit super-Arrhenius diffusion with increasing barrier asymmetry.

Smaller particles maintain Arrhenius diffusion regardless of barrier asymmetry.

The model is applicable to molecular transport in biological and nanofluidic systems.

Abstract

We report results from the molecular dynamics simulations of a binary colloidal mixture subjected to an external potential barrier along one of the spatial directions at low volume fraction, {\phi} = 0.2. The variations in the asymmetry of the external potential barrier do not change the dynamics of the smaller particles, showing Arrhenius diffusion. However, the dynamics of the larger particles shows a crossover from sub-Arrhenius to super-Arrhenius diffusion with the asymmetry in the external potential at the low temperatures and low volume fraction. Super-Arrhenius diffusion is generally observed in the high density systems where the transient cages are present due to dense packing, e.g., supercooled liquids, jammed systems, diffusion through porous membranes, dynamics within the cellular environment, etc. This model can be applied to study the molecular transport across cell membranes, nano-, and micro-channels which are characterized by spatially asymmetric potentials.