Biomedical Engineering Reference
In-Depth Information
3.5
50
µ
m
Sample dimension: L
eff
= 20 mm
and W= 5 mm (100 mm
2
)
VCation: Li
+
1V step @ 1/2 Hz
Improved IPMC (highly permeable)
3.0
2.5
Conventional IPMC (with additives)
Conventional IPMC (no additive)
126
µ
m
2.0
1.5
1.0
0.5
0.0
0
1
2
3
4
5
T (sec)
SE/BSE, 7844264
PtMal, 52
0
20
40
60
80
100
120
µ
m
FIGURE 3.41
SEM micrograph of a stretched IPMNC (19% stretching) and its force per-
formance. Note that an additive, PVP, was added.
occurs. However, at this time we do not have an explanation. The resulting IPMNCs
appear to behave almost the same as the platinum or palladium ones by themselves.
Additional experimental results on stretching and the effect of surface electrodes are
given in figure 3.43.
3.3.7
E
FFECTIVE
S
URFACE
E
LECTRODES
One electrochemical method to study IPMNC artificial muscles is to use the AC imped-
ance method that reveals the structure of an equivalent electric circuit. Figure 3.44
presents a simplified equivalent electric circuit of the typical IPMNC artificial muscle.
In this connection, each single unit circuit (i) is assumed to be linked in a series
of arbitrary surface resistances (
R
ss
) in the surface. This approach is based upon the
experimental observation of the large surface resistance (typically,
/cm;
L
is the length of the surface electrode). In general, it can be assumed that there are
four components to each single unit circuit:
Σ
R
ss
/
L
~ 1-2
Ω
surface-electrode resistance (
R
s
~ tens of ohms per centimeter)
polymer resistance (
R
p
~ hundreds of ohms per millimeter across the membrane)
capacitance related to the ionic polymer and the double layer at the sur-
face-electrode/electrolyte interface (
C
d
~ hundreds of microfarads)
impedance (dynamic resistance,
Z
w
) due to a charge transfer resistance near
the surface electrode
