Mass transport in electrokinetic microflows with the wall reaction affecting the hydrodynamics

Abstract

The mass transport in electrokinetically actuated microchannel flow is interesting when the wall reactions influence the wall potential, thereby affecting the hydrodynamics. This is the first work where the electro-osmotic flow is impacted by the chemical reactions. Since the wall potential is non-uniform, we have compared the results of the classical Poisson–Boltzmann equations with the generalized Poisson–Nernst–Planck model and investigated the applicability within the range of the operating conditions of the problem. The results provide fundamental understanding of the velocity profile within the channel and the wall concentration, which is significantly different from the classical species transport. The wall concentration is dependent on the electrokinetic parameters rather than the Reynolds and Peclet number solely. For constant volumetric flow rate, the resultant electro-osmotic velocity profile is not parabolic and exhibits higher convection close to the wall, leading to reduced solute polarization. The overall mass transport rate can be enhanced by more than two times with respect to non-electrical phenomena. The results will be useful in understanding the physics and provide operational know-how of electrokinetic-based applications related to capillary electrophoresis, electrochromatrogaphy and (bio-)chemical sensing.