Hydrokinetic simulations of nanoscopic precursor films in rough channels

TL;DR

This study uses molecular dynamics and lattice-Boltzmann simulations to investigate nanoscopic precursor films in nano-channels, confirming their formation, dynamics, and potential impact on nano-coating processes.

Contribution

It demonstrates that hydrokinetic lattice-Boltzmann methods accurately model precursor film dynamics, validating their use for complex nano-channel simulations.

Findings

Precursor films follow a square-root law in their dynamics.

Lattice-Boltzmann results agree quantitatively with molecular dynamics.

Precursor films significantly influence nano-coating efficiency.

Abstract

We report on simulations of capillary filling of high-wetting fluids in nano-channels with and without obstacles. We use atomistic (molecular dynamics) and hydrokinetic (lattice-Boltzmann) approaches which point out clear evidence of the formation of thin precursor films, moving ahead of the main capillary front. The dynamics of the precursor films is found to obey a square-root law as the main capillary front, z^2(t) ~ t, although with a larger prefactor, which we find to take the same value for the different geometries (2D-3D) under inspection. The two methods show a quantitative agreement which indicates that the formation and propagation of thin precursors can be handled at a mesoscopic/hydrokinetic level. This can be considered as a validation of the Lattice-Boltzmann (LB) method and opens the possibility of using hydrokinetic methods to explore space-time scales and complex geometries of direct experimental relevance. Then, LB approach is used to study the fluid behaviour in a nano-channel when the precursor film encounters a square obstacle. A complete parametric analysis is performed which suggests that thin-film precursors may have an important influence on the efficiency of nanochannel-coating strategies.