Correlation between surface topography and slippage: a Molecular Dynamics study

TL;DR

This study uses Molecular Dynamics simulations to explore how surface topography, wettability, and pressure influence slippage and friction at the solid-liquid interface, revealing a transition between wetting states and the role of surface edges.

Contribution

It provides new insights into the relationship between surface corrugation, wetting states, and slip behavior, including the impact of pressure and surface features on hydrodynamic boundary conditions.

Findings

Transition between Wenzel and Cassie wetting states observed.

Slip length and boundary position depend on pressure.

Edges of corrugation contribute to friction in the Cassie state.

Abstract

Using Molecular Dynamics simulations of a polymer liquid flowing past flat and patterned surfaces, we investigate the influence of corrugation, wettability and pressure on slippage and friction at the solid-liquid interface. For one-dimensional, rectangular grooves, we observe a gradual crossover between the Wenzel state, where the liquid fills the grooves, and the Cassie state, where the corrugation supports the liquid and the grooves are filled with vapor. Using two independent flow set-ups, we characterize the near-surface flow by the slip length, $\delta$, and the position, $z_\textrm{h}$, at which viscous and frictional stresses are balanced according to Navier's partial slip boundary condition. This hydrodynamic boundary position depends on the pressure inside the channel and may be located above the corrugated surface. In the Cassie state, we observe that the edges of the corrugation contribute to the friction.