On the Comparability of Chemical Structure and Roughness of Nanochannels in Altering Fluid Slippage

TL;DR

This study uses molecular dynamics simulations to explore how surface chemistry and roughness jointly influence water slip length at nanochannels, revealing quantitative relationships and the interplay between wettability and roughness.

Contribution

It establishes a quantitative relation between slip length, surface wettability, and roughness, connecting chemical and physical surface properties in nanochannel fluid dynamics.

Findings

Slip length varies with static contact angle as (1+cosθ)^{-2}.

Surface roughness reduces slip length, following (1+α*)^{-2}.

Chemical and physical surface properties jointly influence interfacial slip.

Abstract

Interfacial hydrodynamic slippage of water depends on both on surface chemistry and roughness. This study tries to connect the effect of chemical property and the physical structure of the surface on the interfacial slippage of water. By performing molecular dynamics simulations (MDS) of Couette flow of water molecules over a reduced Lennard-Jones (LJ) surface, the velocity profile is obtained and extrapolated to get the slip lengths. The slip lengths are measured for various surface-fluid interactions. These interactions are varied by changing the wettability of the surface (characterized by the static contact angle) and its roughness. The slip length variation with the static contact angle as $(1+cos\theta)^{-2}$ is observed. However, it is also observed that the presence of surface roughness always reduces the slip length and it is proposed that the slip length varies with non-dimensionalized average surface roughness as $(1+\alpha^*)^{-2}$ . Thus a relation between the chemical wettability and the physical roughness is established and their coupled interactions modifying slip length is probed.