Transient electro-osmotic and pressure driven flows of two-layer fluids through a slit microchannel

By method of the Laplace transform, this article presents semi-analytical solutions for transient electroosmotic and pressure-driven flows (EOF/PDF) of two-layer fluids between microparallel plates. The linearized Poisson-Boltzmann equation and the Cauchy momentum equation have been solved in this article. At the interface, the Maxwell stress is included as the boundary condition. By numerical computations of the inverse Laplace transform, the effects of dielectric constant ratio ?, density ratio ρ, pressure ratio p, viscosity ratio µ of layer II to layer I, interface zeta potential difference $\Delta \bar \psi$ , interface charge density jump Q, the ratios of maximum electro-osmotic velocity to pressure velocity α, and the normalized pressure gradient B on transient velocity amplitude are presented. We find the velocity amplitude becomes large with the interface zeta potential difference and becomes small with the increase of the viscosity. The velocity will be large with the increases of dielectric constant ratio; the density ratio almost does not influence the EOF velocity. Larger interface charge density jump leads to a strong jump of velocity at the interface. Additionally, the effects of the thickness of fluid layers (h ₁ and h ₂) and pressure gradient on the velocity are also investigated.