Biomedical Engineering Reference
In-Depth Information
J
=−∇
σ
ELp
(2.2)
12
21
QLEKp
=
−
∇
(2.3)
where
are the material conductance and the Darcy permeability, respectively.
A cross-coefficient is usually
σ
and
K
L
=
L
=
L
, experimentally measured to be of the
12
21
order of 10
{(m/s)/(V/m)}.
The simplicity of the preceding equations provides a compact view of fundamental
principles of actuation and sensing of IPMNC. We can illustrate it simply in figure 2.9.
The IPMNC is composed of a perfluorinated ionic polymer, which is chemically
surface composited with a conductive medium such as platinum. A platinum layer
is formed a few microns deep within the perfluorinated ionic polymer.
Typically, the strip of perfluorinated ionic polymer membrane bends toward the
anode (in case of cation-exchange membranes) under the influence of an electric
potential. Also, the appearance of water on the surface of the expansion side and
the disappearance of water on the surface of the contraction side are common. This
electrophoresis-like internal ion-water movement is responsible for creating effective
strains for actuation. Water leakage through the porous Pt electrode reduces the
electromechanical conversion efficiency.
-8
−
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
Hydrated cation-Na(H
2
O)
4
+
Side chain
Water
Fixed anion
Mobile cation
FIGURE 2.9
A schematic of the typical IPMNC and its actuation principle.
