Non-Fickian Interdiffusion of Dynamically Asymmetric Species: A Molecular Dynamics Study

TL;DR

This study investigates the interdiffusion behavior in a binary mixture with dynamically asymmetric species using molecular dynamics, revealing a transition from Fickian to anomalous diffusion as asymmetry increases.

Contribution

It introduces a model combining Molecular Dynamics and Dissipative Particle Dynamics to analyze how dynamic asymmetry affects diffusion behavior.

Findings

Weak asymmetry shows Fickian diffusion.

Strong asymmetry leads to anomalous diffusion.

Crossover behavior between Fickian and Case II diffusion.

Abstract

We use Molecular Dynamics combined with Dissipative Particle Dynamics to construct a model of a binary mixture where the two species differ only in their dynamic properties (friction coefficients). For an asymmetric mixture of slow and fast particles we study the interdiffusion process. The relaxation of the composition profile is investigated in terms of its Fourier coefficients. While for weak asymmetry we observe Fickian behavior, a strongly asymmetric system exhibits clear indications of anomalous diffusion, which occurs in a crossover region between the Cases I (Fickian) and II (sharp front moving with constant velocity), and is close to the Case II limit.