Diffusioosmotic flow of electrolyte solutions in fibrous porous media at arbitrary zeta potential and double-layer thickness

作者：Keh Huan J^*; Hsu Li Y

来源：Microfluidics and Nanofluidics, 2009, 7(6): 773-781.

DOI：10.1007/s10404-009-0435-4

• Diffusioosmosis
• Porous medium
• Charged circular cylinder
• Unit cell model
• Arbitrary electric double layer

The diffusioosmosis of electrolyte solutions in the fibrous medium constructed by a homogeneous assemblage of parallel, charged, circular cylinders caused by a uniform concentration gradient prescribed in their axial direction is studied theoretically. The electric double layers adjacent to the cylinders may have an arbitrary thickness. A unit cell model is used to account for the interaction effect among the cylinders. The electrostatic potential distribution in the fluid phase is determined with an analytical approximation to the solution of the Poisson-Boltzmann equation. By solving the fluid momentum equation with the constraint of no net electric current arising from the co-current diffusion, electric migration, and diffusioosmotic convection of the electrolyte ions, the macroscopic electric field and the fluid velocity in the axial direction induced by the applied electrolyte concentration gradient are obtained semi-analytically as functions of the radial position in a cell in a self-consistent manner. The magnitude and direction of the diffusioosmotic flow relative to the concentration gradient are determined by the combination of the porosity of the array of cylinders, the zeta potential of the cylinders, the properties of the electrolyte solution, and other relevant factors. The fluid velocity generally increases with increasing porosity of the array of cylinders, but there are exceptions. The effects of the radial distribution of the induced electric field and of the ionic convection in the double layers on the diffusioosmotic flow are significant.

• 出版日期2009-12