Wetting and particle adsorption in nanoflows

TL;DR

This study uses molecular dynamics simulations to explore how wetting properties influence particle motion and adsorption in nanofluidic channels, revealing distinct regimes of behavior and the dominance of van der Waals forces in adsorption.

Contribution

It demonstrates the impact of wetting properties on particle dynamics and adsorption in nanoflows, highlighting the transition between continuum-like motion and stick-slip behavior.

Findings

Highly-wetting fluids allow particles to move with continuum-like velocity.

Less-wetting fluids cause particles to adsorb and exhibit stick-slip motion.

Van der Waals forces dominate particle adsorption phenomena.

Abstract

Molecular dynamics simulations are used to study the behavior of closely-fitting spherical and ellipsoidal particles moving through a fluid-filled cylinder at nanometer scales. The particle, the cylinder wall and the fluid solvent are all treated as atomic systems, and special attention is given to the effects of varying the wetting properties of the fluid. Although the modification of the solid-fluid interaction leads to significant changes in the microstructure of the fluid, its transport properties are found to be the same as in bulk. Independently of the shape and relative size of the particle, we find two distinct regimes as a function of the degree of wetting, with a sharp transition between them. In the case of a highly-wetting suspending fluid, the particle moves through the cylinder with an average axial velocity in agreement with that obtained from the solution of the continuum Stokes equations. In contrast, in the case of less-wetting fluids, only the early-time motion of the particle is consistent with continuum dynamics. At later times, the particle is eventually adsorbed onto the wall and subsequently executes an intermittent stick-slip motion.We show that van der Walls forces are the dominant contribution to the particle adsorption phenomenon and that depletion forces are weak enough to allow, in the highly-wetting situation, an initially adsorbed particle to spontaneously desorb.