Biomedical Engineering Reference
In-Depth Information
Stern potential
Nernst potential
-
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
-
+
-
+
+
+
-
+
+
-
+
+
+
-
+
+
+
-
+
+
+
-
-
+
+
+
+
+
-
+
-
+
+
+
+
+
-
Distance from surface
FIGURE 3.3
Equilibrium electrostatic potential in an electrolyte solution bordered by a
plane negative surface. The microstructure of the ionic distribution at the
interface induces the phenomenon of Debye shielding by the ion cloud of the
opposite sign.
Owing to the diculty in solving this equation in a three-dimensional con-
figuration, the hyperbolic sine is often linearized following the Debye-Hueckel
approximation, which is valid for small double-layer potentials (
ϕ
1). On
the basis of a multiscale description of multiphysical flow in porous media,
Moyne and Murad (2002) prove that this equation applies to phenomena at
purely microscopic scale. However, this microscopic effect can have significant
consequences at the macroscale. For instance, when considering symmetric
Cartesian pores, the macroscopical swelling effects observed for cartilagenous
tissues can be explained by Donnan osmotic swelling pressure
π
D
(Donnan
1924) and are governed by the value of this double-layer potential in the sym-
metry plane (Langmuir 1938; Israelachvili 1991).
When advected by the streaming velocity of the fluid, the excess in mobile
charge population in the counterion atmosphere leads to macroscopic observed
electrokinetic phenomena such as streaming currents, resulting from the influ-
ence of fluid movement upon charge flow. In addition, to counterbalance
this apparent charge accumulation and to conserve charge, the movement
of the net charge generates an electric potential, often referred to as stream-
ing potential, which gives rise to other macroscopic electrokinetic phenomena.
Search WWH ::
Custom Search