Diffusioosmosis of electrolyte solutions in fine capillaries
Resource
Colloids and Surfaces A: Physicochem. Eng. Aspects 233(2004), 87–95
Journal
Colloids and Surfaces A: Physicochem. Eng. Aspects 233(2004), 87–95
Pages
-
Date Issued
2004
Date
2004
Author(s)
Ma, Hsien Chen
DOI
246246/2006111501233071
Abstract
An analytical study is presented for the diffusioosmotic flow of an electrolyte solution in a narrow capillary tube or slit caused by a constant
concentration gradient imposed along the axial direction at the steady state. The electric double layer adjacent to the charged capillary wall
may have an arbitrary thickness relative to the capillary radius. The electrostatic potential distribution on a cross section of the capillary is
obtained by solving the linearized Poisson–Boltzmann equation, which applies to the case of low surface potential at the capillary wall. The
macroscopic electric field induced by the imposed electrolyte concentration gradient through the capillary is determined as a function of the
radial position. Closed-form formulas for the fluid velocity profile due to the combination of electroosmotic and chemiosmotic contributions
are derived as the solution of a modified Navier–Stokes equation. The diffusioosmotic velocity can have more than one reversal in direction
over a small range of the surface potential. For a given concentration gradient of electrolyte in a capillary, the fluid-flow rate is not necessarily
to increase with an increase in the electrokinetic radius of the capillary, which is the capillary radius divided by the Debye screening length.
The effect of the radial distribution of the induced axial electric field in the double layer on the diffusioosmotic flow is found to be of dominant
significance in most practical situations.
Subjects
diffusioosmosis
electroosmosis
capillary tube
capillary slit
Publisher
Taipei:National Taiwan University Dept Chem Engn
Type
journal article
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