Diffusiophoresis of Charged Composite Particles (3/3)
Date Issued
2002-08-31
Date
2002-08-31
Author(s)
DOI
902214E002019
Abstract
Driven by applying an electric potential,
temperature, or solute concentration gradient,
the transport behavior of small particles in a
continuous medium and the flow behavior of
fluids in porous media at low Reynolds
numbers are the phenomena known as
“phoretic motion” and “osmotic motion”,
respectively. Diffusiophoresis is the motion
of colloidal particles in an applied interactive
solute concentration gradient and
diffusioosmosis is the fluid flow induced by
the solute gradient in the porous medium.
In this project, the diffusiophoretic and
diffusioosmotic motions are analytically
studied in gradients of a symmetric
electrolyte solute in a homogeneous
suspension of a circular cylinder. The
imposed solute concentration gradient is
constant and can be oriented arbitrarily with
respect to the axes of the cylinders.
Analyses for both thin and arbitrary
electric double layers surrounding the
particle are presented. In the
thin-double-layer analysis, the thickness of
the double layer is assumed to be small
relative to the radius of the particle, but the
polarization effect of the diffuse ions in the
double layer is incorporated. In the
arbitrary-double-layer analysis, the double
layer may have an arbitrary thickness relative
to the radius of the particle, and only the
particle surface with a small surface charge
density (or zeta potential) is considered. The effects of interaction among individual
particles are taken into explicit account by
employing a unit cell model. Analytical
expressions for the diffusioosmotic velocity
of the bulk fluid as functions of the porosity
of the ordered array of cylinders are obtained
for various cases. For cylinders with an
arbitrary double-layer thickness, the
expressions for the diffusioosmotic velocity
are obtained in closed form correct to the
second order of their surface charge density
or zeta potential. A comparison of the
results of the diffusioosmotic mobility
obtained in the thin-layer analysis and in the
arbitrary-layer analysis for the cell model is
made. Again, the diffusioosmosis results
predicted by the thin-double-layer analysis
can be in significant errors when the value of
the electric double layer thickness parameter
ka is less than about 20.
Subjects
Cylindrical particle
Diffusio-phoresis
Diffusioosmosis
Unit cell model
Publisher
臺北市：國立臺灣大學化學工程學系暨研究所
Type
report
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