Kinetics of Surface Enrichment: A Molecular Dynamics Study

TL;DR

This study uses molecular dynamics simulations to analyze the kinetics of surface enrichment in a mixture, revealing a double-exponential profile and the influence of hydrodynamics on growth behavior.

Contribution

It provides new insights into the dynamic behavior of surface enrichment, including the crossover in growth exponents due to hydrodynamic effects.

Findings

Surface enrichment profiles exhibit double-exponential behavior.

Hydrodynamics cause a crossover in growth exponent from 0.5 to 1.0.

Two characteristic length scales govern the enrichment process.

Abstract

We use molecular dynamics (MD) to study the kinetics of surface enrichment (SE) in a stable homogeneous mixture (AB), placed in contact with a surface which preferentially attracts A. The SE profiles show a characteristic double-exponential behavior with two length scales: \xi_-, which rapidly saturates to its equilibrium value, and \xi_+, which diverges as a power-law with time (\xi_+ \sim t^\theta). We find that hydrodynamic effects result in a crossover of the growth exponent from \theta \simeq 0.5 to \theta \simeq 1.0. There is also a corresponding crossover in the growth dynamics of the SE-layer thickness.