Biomedical Engineering Reference
In-Depth Information
Let us first emphasize the key role that water plays within the ionic polymer
that determines the physical chemistry of the ion-exchange polymers. When the
polymer is dry, strong interactions between the counter-ions and the fixed ionic
groups of the polymer are dominant. As a result, the ion-exchange polymer exhibits
low conductivity. Once the ion-exchange polymer is swollen (or wet), it solvates the
counter-ions and the fixed ionic groups such that it lowers the interactions between
cations. Under these circumstances, the material conductivity dramatically increases.
Note that routinely measured mechanical properties (i.e., thickness, tensile stress,
burst strength, hydrostatic permeability, etc.) are important for inspecting ion-
exchange polymers. Important parameters to affect these properties include the
pretreatment of the polymers, the type of electrolyte solutions, and the temperature.
3.2.2
W
S
IPMNC B
M
ATER
TRUCTURE
WITHIN
THE
ASE
ATERIALS
In this section, the critical role of the water content within the IPMNC base materials
is emphasized so as to determine their properties as well as their polymer structures.
Also, the relationship between the electrolyte solutions in connection with the polymer
properties is discussed. In table 3.3, a number of important ion-exchange polymers
that have been used as base material for the IPMNC artificial muscles are presented
along with their characteristics (Oguro, Asaka, and Takenaka, 1993; Shahinpoor, Kim
et al., 2002). In this table, actuation performance testing was performed with an
IPMNC strip in a cantilever configuration while applying the electric field at the built-
in end (fig. 3.4).
As depicted in figure 3.4, an experiment was set to measure the blocking force
per a given electric field. A PC-based test platform was used for actuation tests of all
samples. A multi-I/O board and corresponding SCXI devices were conjugated to a
load cell. The signal generation system utilizes LabView's prewritten
Function Gen-
erator
virtual instrument. A power amplifier amplifies the initial voltage. The output
voltage from the power amplifier is supplied to the test sample for actuation. A digital
oscilloscope was simultaneously used to monitor/store the input and output waveforms.
The IPMNC test sample was attached at one end to the load cell while the other end
was placed at the contact platinum electrode, which typically formed the jaws of a
forceps. The blocking force was measured at zero displacement. The IPMNC test
samples were positioned horizontally so as to eliminate the gravity influence.
TABLE 3.3
Important Ionic Polymers Used as IPMNCs
Water
content
H
O/fixed
charge
Cation
type
Actuation
performance
2
Polymer type
Nafion-117
0.14
~12
Li
+
Perfluorinated sulfonate
> 2 gf
-cm/1 V
max
Neosepta C66
0.42
~9
Li
+
Polystyrene sulfonate
> 1 gf
-cm/1 V
max
Ionics CR-67
0.46
~12
Li
+
Polystyrene sulfonate/
an acrylic fabric
> 0.5 gf
-cm/1 V
max
ERI-S1
0.17
~11
Li
+
Perfluorinated sulfonate
> 2.5 gf
-cm/1 V
max
