Electro-hydrodynamics near Hydrophobic Surfaces

TL;DR

This paper investigates how electro-osmotic flow near hydrophobic surfaces is influenced by surface charge mobility, revealing that slip and charge dynamics significantly alter flow behavior and zeta-potential interpretation.

Contribution

It introduces a theoretical framework for electro-hydrodynamic boundary conditions at slipping interfaces considering charge mobility, supported by particle dynamics simulations.

Findings

Flow amplification with immobile charges due to slip

Electric forces influence flow near mobile charges

New interpretation of zeta-potential for hydrophobic surfaces

Abstract

We show that an electro-osmotic flow near the slippery hydrophobic surface depends strongly on the mobility of surface charges, which are balanced by counter-ions of the electrostatic diffuse layer. For a hydrophobic surface with immobile charges the fluid transport is considerably amplified by the existence of a hydrodynamic slippage. In contrast, near the hydrophobic surface with mobile adsorbed charges it is also controlled by an additional electric force, which increases the shear stress at the slipping interface. To account for this, we formulate electro-hydrodynamic boundary conditions at the slipping interface, which should be applied to quantify electro-osmotic flows instead of hydrodynamic boundary conditions. Our theoretical predictions are fully supported by dissipative particle dynamics simulations with explicit charges. These results lead to a new interpretation of zeta-potential of hydrophobic surfaces.