Biomedical Engineering Reference
In-Depth Information
2.0
ERI-S1 muscle (5 Pt-1 Pt/PVP)
L
o
= 1 inch
Input = Sine
1.8
0.1 Hz
1.6
1.4
1.2
0.2 Hz
1.0
0.5 Hz
0.8
0.6
0.4
0.2
0.0
0
1000
2000
3000
4000
5000
6000
7000
8000
2.0
ERI-S1 muscle (5 Pt-1 Pt/PVP)
L
o
= 1.5 inch
Input = Sine
1.8
1.6
1.4
1.2
0.1 Hz
0.2 Hz
1.0
0.8
0.5 Hz
0.6
0.4
0.2
0.0
0
1000
2000
3000
4000
5000
6000
7000
8000
E (V/m)
FIGURE 6.30
Actuation under a low-frequency electric field to minimize the effect of loose
water back diffusion.
Other parameters have been experimentally measured to be K ~ 10
-18
m
2
/CP,
σ
~ 1 A/mV or S/m. Figure 6.31 depicts a more detailed set of data pertaining to
Onsager coefficient
L
.
The role of loose water (nonhydrated on the cations) is also of interest to our
experimental and theoretical investigations. In the presence of loose water in the
network and within and in the vicinity of ionic clusters under a step-voltage activa-
tion, there is a clear final deformation or tip deflection accompanied by a small
relaxation due to back diffusion of such loose water back towards the anode. In other
words, the loose water is dragged by the hydrated cations, similar to the added mass
effect in the fluid mechanics of moving objects in a viscous fluid. Thus, once the
step voltage causes all cations to move towards the cathode and accumulate there
and finally come to osmotic equilibrium, the loose water simply diffuses back due
to the local pressure gradient. This causes a slight back relaxation of the bending
deformation of the IPMNC strip (see fig. 6.32a). If the strip is dry enough to be just
devoid of loose water, no such back relaxation occurs (see fig. 6.32b). In order to
achieve this, the IPMNC strip needs to be dried partially in order to remove any
loose water in the network. This objective has been successfully achieved using a
controlled-humidity environmental chamber.
