Biomedical Engineering Reference
In-Depth Information
200
µ
m
20
µ
m
28.5
µ
m
FIGURE 2.6
Two SEM micrographs showing the cross-section (left) and close-up (right) of
a typical IPMNC.
time-dependent concentrations of the salt and the reducing agents (applying the
Taguchi technique to identify the optimum process parameters seems quite attractive;
see Peace, 1993). The primary reaction is
LiBH
+ 4[
Pt
(
NH
)
]
2+
+ 8
OH
-
⇒
4
Pt
o
+ 16
NH
+
LiBO
+ 6
H
O
(2.1)
4
3
4
3
2
2
In the subsequent surface electroding process, multiple reducing agents are
introduced (under optimized concentrations) to carry out the reducing reaction sim-
ilar to equation (2.1), in addition to the platinum layer formed by the initial com-
positing process. This is clearly shown in figure 2.4 (bottom right), where the
roughened surface disappears. In general, the majority of platinum salts stays in the
solution and precedes the reducing reactions and production of platinum metal. Other
metals (or conductive media) also successfully used include palladium, silver, gold,
carbon, graphite, and nanotubes.
To characterize the surface morphology of the IPMNC, atomic force microscopy
(AFM) can be used. Its capability to image the surface of the IPMNC directly can
provide detailed information with a resolution of a few nanometers. In figure 2.7, a
number of representative AFM images (its surface analysis) reveal the surface mor-
phology of the IPMNCs. As can be seen, depending on the initial surface roughening,
the surface is characterized by the granular appearance of platinum metal with a
peak/valley depth of approximately 50 nm. This granular nanoroughness is respon-
sible for producing a high level of electric resistance, yet provides a porous layer
that allows water movement in and out of the membrane.
During the AFM study, it was also found that platinum particles are dense and,
to some extent, possess coagulated shapes. Therefore, the study was extended to
utilize TEM (transmission electron microscopy) to determine the size of the depos-
ited platinum particles. Figure 2.8 shows a TEM image on the penetrating edge of
the IPMNC. The sample was carefully prepared in the form of a small size and was
ion beam treated. The average particle size was found to be around 47 nm.
A recent study by de Gennes et al. (2000) has presented the standard Onsager
formulation on the fundamental principle of IPMNC actuation/sensing phenomena
using linear irreversible thermodynamics. When static conditions are imposed, a
simple description of
mechanoelectric effect
is possible based upon two forms of
