Diffusioosmosis of Electrolyte Solutions in Fine Capillaries
Date Issued
2007
Date
2007
Author(s)
Ma, Hsien-Chen
DOI
en-US
Abstract
In general, driving forces for the fluid transport through micropores include dynamic pressure differences between the two ends of a capillary pore (convection), concentration differences of an impermeable solute between the two bulk solutions outside the pores (osmosis), and tangential electric fields that interact with the electric double layer adjacent to a charged pore wall (electroosmosis). Another driving force for the flow of liquid solutions in a capillary pore, which has commanded less attention, involves concentration gradients of a permeable solute along the capillary that interacts with the pore wall. The fluid motion associated with this mechanism is termed diffusioosmosis.
The steady diffusioosmotic flows of an electrolyte solution along a charged plane wall, in a capillary slit, in a capillary tube, and in a slit with its walls coated with polyelectrolyte layers generated by an imposed tangential concentration gradient are theoretically examined in this study. The charged walls may have either a constant surface potential or a constant surface charge density of an arbitrary quantity. The electric double layers adjacent to the charged walls may have an arbitrary thickness and their electrostatic potential distributions are governed by the Poisson-Boltzmann equation. Solving a modified Navier-Stokes equation with the constraint of no net electric current arising from the cocurrent diffusion, electric migration, and diffusioosmotic convection of the electrolyte ions, the macroscopic electric field and the fluid velocity in the tangential direction induced by the imposed electrolyte concentration gradient are obtained as functions of the lateral position for various cases.
The results indicate that the effect of the deviation of the local induced tangential electric field inside the double layer from its bulk-phase quantity and the relaxation effect on the diffusioosmotic velocity of the fluid are significant in most practical situations, even for the case of very thin double layer.
Subjects
擴散滲透
電滲透
任意電雙層厚度
鬆弛效應
細微孔隙
Diffusioosmosis
Electroosmosis
Arbitrary double-layer thickness
Relaxation effect
Fine capillary
Polyelectrolyte-coated capillary
Type
thesis