Steric effects on electroosmotic flow in soft nanochannels

A numerical solution is derived of the mixed pressure and electroosmotically driven flow in a soft nanochannel considering the steric effect within electric double layer. The electric potential and the velocity distributions are described by the modified Poisson–Boltzmann equation and the modified Navier–Stokes equation under the conditions of boundary slip and constant charge density on the walls. By  using the finite difference method, the numerical solutions of the electric potential, velocity and the volumetric flow rate are obtained. Results show that the electric potential increases with the steric parameter. The velocity decreases with the steric parameter for lower surface charge density, while opposite trend can be found for higher surface charge density. We compare the results of soft and rigid nanochannels and find the velocity in the soft nanochannel is larger than that in the rigid one except for the case of higher surface charge density.