Steady/unsteady electroosmotic flow through nanochannel filled with electrolyte solution surrounded by an immiscible liquid

Abstract

This article deals with the electroosmotic flow through nanochannel filled with electrolyte solution surrounded by an immiscible oil layer where the fluid is driven by either DC or AC electric field. The walls of the nanochannel are considered to bear a constant negative surface charge. Additional mobile ions with positive polarity are present in the surface oil layer. The electrostatic potential can be obtained from the nonlinear Poisson-Boltzmann equation. With the known electric potential, we calculate the axial velocity distribution from the unsteady Stokes equation. The effects of intrinsic parameters on the overall electrostatic behavior as well as velocity distribution are discussed in a great detail. We identify several interesting key features of the flow distributions under externally applied DC or AC electric field. For lower range of Debye-Huckel parameter, the overlap of adjacent electric double layers significantly affects the flow profile. In addition for externally applied sinusoidal AC electric field, a finite settling time is required to diffuse the momentum of the fluid from the adjacent region of the channel wall to the bulk fluid. As a result, a phase shift between the applied electric field and velocity field may occur. Under AC electric field, the oscillatory behavior of the axial velocity is further investigated.