Biomedical Engineering Reference
In-Depth Information
H
2
O
+
+
Hydrated cation-Na(H
2
O)
4
+
Water
Pt particle
FIGURE 3.27
(b)
A schematic showing how the loose and ion-hydrated water is gushing out
under an imposed voltage.
strains from effectively generating larger forces similar to a leaky hydraulic jack.
Therefore, a key engineering problem is how to prevent such a water (solvent)
leakage out of the porous electrode. Here, we describe a successfully developed
process technique to address such a leakage problem so as to manufacture a high-
output force IPMNC.
In these materials, a circulatory system of hydrated cations and water exists that
may be employed to do a variety of functions with IPMNCs. Figure 3.27(b) depicts
a schematic to show how water and hydrated cations can gush out of the surfaces
of IPMNCs under an imposed voltage.
As discussed in a previous paper (Shahinpoor and Kim, 2001g), the nominal size
of primary platinum particles of the IPMNC is found to be around 40-60 nm, which
is much larger than that of incipient particles associated with ion clusters (~5 nm).
Thus, this finding leads to a firm conclusion that incipient particles coagulate during
the chemical reduction process and eventually grow large. If so, one can realize a
significant potential to control this process (in terms of platinum particle penetration,
size, and distribution). To do so could be achieved by introducing effective dispersing
agents (additives) during the chemical reduction process. One can anticipate that the
effective additives should enhance the dispersion of platinum particles within the
material and finally reduce coagulation. As a result, a better platinum particle pene-
tration into the material can be realized. This also creates a somewhat smaller particle
size with fairly good distribution. Thus, the water leakage out of the surface electrode
could be significantly reduced. A recent observation by Shahinpoor and Kim has been
the identification of a number of effective dispersion agents or dispersants.
As a successful outcome, the use of the effective dispersing agent during the
platinum metalization process has given dramatically improved force characteristics
showing a much sharper response (smaller time constants) to the input electric
impetus and a dramatically increased force generation.
