Net electroosmotic flow along an uncharged polarizable surface under DC electric field.

To induce a net electroosmotic flow (EOF) in the vicinity of an uncharged polarizable surface or around an immersed polarizable body by a comparatively weak DC electric field, a symmetry-breaking phenomenon needs to be invoked. Previous studies reveal that the symmetry can be broken either via the geometry of the surface/body or by modifying the surface properties. We find that even without such types of symmetry breaking, a substantial net EOF develops under a weak DC electric field in a charge-asymmetric electrolyte with different valences of anions and cations. We numerically solve the coupled set of Poisson-Nernst-Planck and Navier-Stokes equations around a spherical particle and in a nanochannel, especially for the case that the solid material is highly electrically polarizable. We also derive an analytical expression for the electrophoretic mobility of the particle in the limit of very high dielectric permittivity and thin electric double layer. The derived scaling relationships indicate that giant net flow velocities of the order of meters per second may occur in the nanochannel, which opens up new opportunities for future research.