Macroscale description of electrokinetic flows at large zeta potentials: nonlinear surface conduction

Area of Science:

• Physical Chemistry
• Surface Science
• Electrochemistry

Background:

• Electrokinetic phenomena are crucial for understanding fluid transport near charged surfaces.
• The thin-double-layer limit typically simplifies these analyses.
• Highly charged surfaces present unique challenges due to large ion concentrations.

Purpose of the Study:

• To develop a generic, non-linear analysis of electrokinetic transport for highly charged dielectric surfaces.
• To investigate the impact of large counterion concentrations and associated surface currents.
• To address limitations of previous weak-field approximations.

Main Methods:

• Thin-double-layer analysis beyond weak-field linearization.
• Identification of an internal boundary layer within the diffuse double layer.
• Development of a multiscale description for electrokinetic transport.

Main Results:

• High surface charge leads to an internal boundary layer with distinct ionic concentration and electric field scaling.
• Surface conduction is localized within this internal layer.
• Nonlinear bulk transport and bulk concentration polarization arise, modifying electrokinetic phenomena.

Conclusions:

• The study provides a more accurate model for electrokinetic transport at highly charged surfaces.
• It highlights the emergence of nonlinear effects and an internal boundary layer.
• It identifies ambiguities in the 'particle zeta potential' concept for nonuniform distributions.