Streaming potential and electroviscous effects in periodical pressure-driven microchannel flow

An analytical solution for pressure-driven periodical electrokinetic flows in a two-dimensional uniform microchannel is presented based on the Poisson-Boltzmann equation for electrical double layer and the Navier-Stokes equations for incompressible viscous fluid. The analytical results indicate that the periodical streaming potential strongly depends on the periodical Reynolds number (Re=omega h(2)/nu) which is a function of the frequency, the channel size, and the kinetic viscosity of fluids. For Re < 1, the streaming potential behaves similarly to that of steady flow, whereas it decreases rapidly with Re as Re>1. In addition, the electroviscous force affects greatly both the periodical flow and streaming potential, particularly when the nondimensional electrokinetic diameter kappa h is small. The electroviscous force has been found to depend on three factors: first, the electroviscous parameter, which is defined as the ratio of the maximum electroviscous force to the pressure gradient; second, the distribution parameter describing the distribution of the electroviscous force over the cross section of the microchannel; third, the coupling coefficient, which is a function of both the periodical Reynolds number and electroviscous parameter, determining both the amplitude attenuation and phase offset of the electroviscous force. (C) 2008 American Institute of Physics.