# Sub-Nanometer Interfacial Hydrodynamics: The Interplay of Interfacial Viscosity and Surface Friction

## TL;DR

This paper develops a framework to accurately model interfacial flow at the nanoscale by incorporating position-dependent surface friction and viscosity profiles derived from molecular dynamics simulations, revealing exponential relationships with adhesion work.

## Contribution

It introduces a novel approach to account for interfacial viscosity and surface friction in nanofluidic flow modeling, bridging molecular dynamics and continuum hydrodynamics.

## Key findings

- Power-law relationships among friction, viscosity, and depletion length.
- Exponential dependence of interfacial properties on work of adhesion.
- Validated framework for sub-nanometer interfacial flow modeling.

## Abstract

For an accurate description of nanofluidic systems, it is crucial to account for the transport properties of liquids at surfaces on sub-nanometer scales, where classical hydrodynamics fails due to the finite range of surface-liquid interactions and modifications of the local viscosity. We show how to account for both via generalized, position-dependent surface-friction and interfacial viscosity profiles, which enables the accurate description of interfacial flow on the nanoscale using the Stokes equation. Such profiles are extracted from non-equilibrium molecular dynamics simulations of water on polar, non-polar, fluorinated, and unfluorinated alkane and alcohol self-assembled monolayers of widely varying wetting characteristics. Power-law relationships among the Navier friction coefficient, interfacial viscosity excess, and depletion length are revealed, and these are each found to be exponential in the work of adhesion. Our framework forms the basis for describing sub-nanometer fluid flow at interfaces with implications for electrokinetics, biophysics, and nanofluidics.