Electrokinetic pumping effects of charged porous media in microchannels using the lattice Poisson-Boltzmann method.

The electrokinetic pumping characteristics of nanoscale charged porous media packed in microchannels are investigated using a mesoscopic evolution method. When the pore size of porous media is comparable to the thickness of electric double layer, the effects of particle surface potentials on the bulk electric potential distribution will not be negligible. The lattice Poisson-Boltzmann method provides an accurate numerical solution for such problems, which combines two sets of lattice evolution methods solving the nonlinear Poisson-Boltzmann equation for electric potential distribution and the Navier-Stokes equations for fluid flow, respectively. The effects of the finite particle size, the bulk ionic concentration, the external electric field strength and the surface potentials on the electroosmotic micropump performances are therefore studied. The results show that for a certain porosity the maximum pumping pressure is inversely proportional to the particle diameter and the flow rate under zero pressure drop increases with the particle size. The pumping flow rate decreases with the backpressure yet increases with the external electric field strength, linearly respectively. The averaged flow rate increases with the bulk ionic concentration and the particle surface potential, but is slightly influenced by the surface potentials of channel walls. The numerical results agree with the published experimental data while some results deviate from the predictions based on the macroscopic linear assumptions.