Biomedical Engineering Reference
In-Depth Information
Figure 2.3 shows dynamic sensing or transduction response of a strip of an
IPMNC strip in a cantilever form subject to a dynamic impact loading in a cantilever
configuration. A damped electric response is observed and is highly repeatable with
a high bandwidth of up to tens of kilohertz. Such direct mechanoelectric behaviors
are related to the endo-ionic mobility due to imposed stresses.
Manufacturing an IPMNC begins with selection of an appropriate ionic poly-
meric material. Often, these materials are manufactured from polymers that consist
of fixed covalent ionic groups. The currently available ionic polymeric materials that
are convenient to be used as IPMNCs are
Perfluorinated alkenes with short side chains terminated by ionic groups
(typically sulfonate or carboxylate (SO
) for cation exchange or
ammonium cations for anion exchange (see fig. 2.4). The large polymer
backbones determine their mechanical strength. Short side chains provide
ionic groups that interact with water and the passage of appropriate ions.
Styrene/divinylbenzene-based polymers in which the ionic groups have been
substituted from the phenyl rings where the nitrogen atom is fixed to an
ionic group. These polymers are highly cross-linked and are rigid.
3
-
or COO
-
In perfluorinated sulfonic acid polymers, there are relatively few fixed ionic
groups. They are located at the end of side chains so as to position them in their
preferred orientation to some extent. Therefore, they can create hydrophilic nanochan-
nels, so-called
(Gierke et al., 1982). Such configurations are drasti-
cally different in other polymers such as styrene/divinylbenzene families that limit,
primarily by cross-linking, the ability of the ionic polymers to expand (due to their
hydrophilic nature).
The preparation of ionic polymer-metal composites requires extensive laboratory
work including metal compositing by means of chemical reduction. State-of-the-art
IPMNC manufacturing techniques (Shahinpoor and Mojarrad, 2000) incorporate two
distinct preparation processes: first, the
cluster networks
initial compositing process
and then the
. Different preparation processes result in morphologies
of precipitated platinum that are significantly different. Figure 2.5 shows illustrative
schematics of two different preparation processes (top left and bottom left) and two
top-view scanning electron micrographs (SEMs) for the platinum surface electrode
(top right and bottom right).
surface electroding process
CFO)
m
CF
2
CF
2
SO
-
(CF
2
CF
2
)
n
CFO(CF
2
Na
+
−
−
CF
2
CF
3
or
CFO)
m
(CF
2
)
n
SO
3
−
(CF
2
CF
2
)
x
−
CFO(CF
2
−
Na
+
CF
2
CF
3
FIGURE 2.4
Perfluorinated sulfonic acid polymers.
