Coupling Electroosmotic and Pressure-Driven Flow in Porous Media for Enhanced Mixing

We investigate the interaction between electroosmotic and pressure-driven flows in heterogeneous porous media using Hele-Shaw cell experiments, focusing on how heterogeneity influences recirculation and mixing. Electroosmotic flow arises when an electric field is applied along a charged surface in contact with an electrolyte, creating effective slip. We show that pressure-driven flow dominates in high-permeability regions, while electroosmotic flow prevails in narrow zones, leading to recirculation in regions with permeability gradient. To quantify these effects, we estimate electrokinetic mobility, hydraulic conductivity, and zeta potential by balancing electroosmotic flow against capillary resistance. Using a simple electroosmotic droplet-switch setup with electrodes across a microchannel, we measure interface deflections to extract these coefficients, allowing direct comparison between experiments and simulations. Our work demonstrates that the interplay between electroosmotic and pressure-driven flows can be utilized to enhance mixing in porous media.