Universal Fast Mode and Potential-dependent Regimes in Wetting Kinetics

TL;DR

This study uses molecular dynamics simulations to reveal universal fast-mode wetting kinetics with potential-dependent regimes, resolving previous controversies and identifying distinct early-stage growth behaviors for different surface potentials.

Contribution

The paper demonstrates the existence of universal fast-mode wetting kinetics and clarifies the influence of long-ranged and short-ranged surface potentials on early-stage wetting behavior.

Findings

Power-law growth of wetting-layer thickness with exponent 1/(n+2) for long-ranged potentials

Universal fast-mode regime with growth exponent 3/2

Logarithmic growth observed for short-ranged potentials

Abstract

We present simulation results from a comprehensive molecular dynamics (MD) study of surface-directed spinodal decomposition (SDSD) in unstable symmetric binary mixtures at wetting surfaces. We consider long-ranged and short-ranged surface fields to investigate the early-stage wetting kinetics. The attractive part of the long-ranged potential is of the form $V(z) \sim z^{-n}$, where $z$ is the distance from the surface and $n$ is the power-law exponent. We find that the wetting-layer thickness $R_1(t)$ at very early times exhibits a power-law growth with an exponent $\alpha = 1/(n+2)$. It then crosses over to a universal fast-mode regime with $\alpha=3/2$. In contrast, for the short-ranged surface potential, a logarithmic behavior in $R_1(t)$ is observed at initial times. Remarkably, similar rapid growth is seen in this case too. We provide phenomenological arguments to understand these growth laws. Our MD results firmly establish the existence of universal fast-mode kinetics and settle the related controversy.