An Ohmic model for electrokinetic flows of binary asymmetric electrolytes

• We derive a general model for electrokinetic flows including diffusive currents.
• We review free charge dynamics and distribution in electric double layers.
• Our model describes a variety of common electrokinetic flows.
• We discuss the effects of electrolyte asymmetry in electrokinetic flows.

The transport of electrolytes in electric fields is a ubiquitous phenomenon commonly harnessed in microfluidics. A classic leaky dielectric model for flow generated by electric fields accurately predicts electrohydrodynamic transport phenomenon but is valid for millimeter-scale and larger flows and at relatively low ionic strength. Here, we derive and use a modified version of this model to sub-millimeter scales more relevant to microfluidics, where diffusive transport of charged species becomes non-negligible. We formulate a general equation set, the modified Ohmic model, applicable to the transport of binary, asymmetric electrolytes. We leverage this model to describe a variety of microfluidic electrokinetic systems, including DC electroosmosis, alternating current electrokinetics (ACEK) and induced-charge electroosmosis (ICEO), thus highlighting some unifying principles of these flows.

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