Effect of pressure-driven flow on electroosmotic flow and electrokinetic mass transport in microchannels

The coupling of pressure-driven flow (PDF) and electroosmotic flow (EOF) has been widely applied in the field of microfluidics. However, the adverse effects of pressure induced by PDF on EOF in a confined space cannot be ignored. Herein, the interactions of these two streams when the Reynolds number (Re) varies from 0.1 to 10 are systematically explored through numerical simulations to gain an in-depth understanding of the mechanism of the pressure effect on mass species transport and to generate optimal separation of samples. The simulation results show that the length of the sample increases linearly and the molecular diffusion is accelerated due to the pressure effect caused by the EOF channel structure and PDF extrusion, which reduces the separation quality and even leads to the failure of electrophoresis. However, the deformation of the sample cannot be effectively resisted by increasing the applied voltage. A better separation effect can be obtained only when Re=0.1. To surmount the above disadvantages, a novel porous polymer plug with pores smaller than 5 μm that provides a region that has high flow resistance but allows the electromigration of charged analytes is established in the EOF channel. The experimental results show that this plug can effectively neutralize the EOF outlet pressure when Re≤5. The shape of the sample is not distorted and the maximum gray values decreased by 26%, 30% and 49% respectively in 7 s when Re=0.1, 1 and 5, which are much better than the results without the plug.