Evidence of thin-film precursors formation in hydrokinetic and atomistic simulations of nano-channel capillary filling

TL;DR

This study uses hydrokinetic and atomistic simulations to demonstrate the formation and dynamics of thin precursor films in nano-channel capillary filling, showing their behavior follows the Lucas-Washburn law.

Contribution

It provides the first clear evidence of precursor film formation in nano-channels using combined hydrokinetic and molecular dynamics simulations, validating a mesoscopic modeling approach.

Findings

Precursor films move ahead of the main capillary front.

Precursor film thickness is about one tenth of the capillary diameter.

Hydrokinetic and molecular dynamics methods show quantitative agreement.

Abstract

We present hydrokinetic Lattice Boltzmann and Molecular Dynamics simulations of capillary filling of high-wetting fluids in nano-channels, which provide 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 the Lucas-Washburn law as the main capillary front, z2(t) proportional to t, although with a larger prefactor, which we find to take the same value for both geometries under inspection. Both hydrokinetic and Molecular Dynamics approaches indicate a precursor film thickness of the order of one tenth of the capillary diameter. The quantitative agreement between the hydrokinetic and atomistic methods indicates that the formation and propagation of thin precursors can be handled at a mesoscopic/hydrokinetic level, thereby opening the possibility of using hydrokinetic methods to space-time scales and complex geometries of direct experimental relevance.