Concentration polarization, surface currents, and bulk advection in a microchannel

Area of Science:

• Electrochemistry
• Fluid Dynamics
• Chemical Engineering

Background:

• Concentration polarization is a key phenomenon in microfluidic devices.
• Understanding salt transport and overlimiting currents is crucial for device performance.
• Existing models do not fully capture the interplay between bulk flow and surface phenomena.

Purpose of the Study:

• To comprehensively analyze salt transport and overlimiting currents in microchannels.
• To investigate the coupling between bulk advection and surface current.
• To extend analytical models for overlimiting currents.

Main Methods:

• Full numerical simulations of the coupled Poisson-Nernst-Planck-Stokes problem.
• Development of analytical models for limiting cases (long channel, negligible surface charge).
• Inclusion of diffusion and advection effects in the diffuse layer.

Main Results:

• Discovery of strong coupling between bulk advection and surface current.
• Demonstration that bulk advection is suppressed without a surface current.
• Validation of numerical simulations with analytical models.
• Extension of analytical models to include surface conduction effects.

Conclusions:

• The interplay between bulk advection and surface current is critical in microchannel transport.
• Accurate modeling requires considering these coupled phenomena.
• The extended analytical model provides a better understanding of overlimiting currents.