Biomedical Engineering Reference
In-Depth Information
Water of hydration (10.4)
Free water (7.7)
We akly bounded
water (1.5)
FIGURE 3.8
form). The total
number of water molecules is 19.6. (Davis, T. A. et al. 1997. A First Course in Ion Permeable
Membranes. Electrochemical consultancy.)
Number of water molecules per an ionic group in Nafion (Li
+
the DSC responses for Nafion-117 (Li
form) for cooling. At the high water content,
a sharp peak (peak 1) corresponds to the water freezing at around 240 K. In other
words, some water freezes at this temperature, 30 to 40
+
C lower than the normal
water-freezing temperature (type 3). Also, it shows another peak that attributes to
freezing of more ordered (freezing bound) water, which appears to be weakly
bounded to ions (type 2). Note that such temperatures are much lower than that of
normal water freezing. However, more importantly, this DSC experiment overlooks
another type of water present in Nafion (type 1) that does not freeze and is water in
the hydration shell of the cations (or anions). The amount of these three different
types of water for Nafion is given in figure 3.8. One may note that the greater
hydration expands the lattice to bring more water into the network.
For styrene/divinylbenzene type polymers, all the water is bound to ions and
therefore no phase changes associated with freezing can be realized. Thus, the
styrene/divinylbenzene type polymers have more ions and are considered continuous
structures along with closer ion spacing. In DSC data, usually all the peaks are small
and broad.
°
3.3
MANUFACTURING TECHNIQUES
3.3.1
I
G
N
ENERAL
The current state-of-the-art IPMNC manufacturing technique (Shahinpoor and Mojarrad,
2000; Asaka et al., 1995; Shahinpoor and Kim, 2001g; Kim and Shahinpoor,
2003a) incorporates two distinct preparation processes:
initial compositing pro-
. Due to different preparation processes,
morphologies of precipitated platinum are significantly different. Figure 3.9
shows illustrative schematics of two different preparation processes (top left and
bottom left) and two top-view SEM micrographs for the platinum surface elec-
trode (top right and bottom right).
cess
and
surface electroding process
