Biomedical Engineering Reference
In-Depth Information
R
ss
R
ss
R
s
R
s
R
s
R
p
R
p
R
p
C
d
C
d
C
d
Z
w
Z
w
Z
w
R
s
R
s
R
s
R
ss
R
ss
Single unit-circuit
(i
- 1)
(i)
(i
+ 1)
10000
1000
100
10
1
0.1
0.01
0
2468
10
12 4
Penetration depth (
µ
m)
FIGURE 2.15
A possible equivalent electric circuit of typical IPMNCA (top) and measured
surface resistance,
R
s
, as a function of platinum penetration depth (bottom). Note that SEM
was used to estimate the penetration depth of platinum in the membrane. The four-probe
method was used to measure the surface resistance,
R
s
, of the IPMNCs. Clearly, the deeper
the penetration is, the lower the surface resistance is.
Realizing that water contained in the perfluorinated IPMNC network is the sole
solvent that can create useful strains in the actuation mode, another issue to deal with
is the so-called “decomposition voltage.” As can be clearly seen in figure 2.16, the
decomposition voltage is the minimum voltage at which significant electrolysis occurs.
This figure contains the graph of steady-state current,
I
, versus applied DC
voltage,
E
app
, showing that as the voltage increases, there is little change in current
(obeying Faraday's law). However, a remarkable increase in DC current is observed
with a small change of voltage. Even though the intrinsic voltage causing water
electrolysis is about 1.23 V, a small overpotential (approximately 0.3-0.5 V) was
observed. It should be noted that such water electrolysis leads to lower thermody-
namic efficiency of the IPMNC.
