Biomedical Engineering Reference
In-Depth Information
Scope
Power
amplifier
Computer w/Daq
SCXI-I/O
Load cell
IPMC artificial muscle
Top-view
FIGURE 3.4
Experimental setup used.
H
2
O peak
Peak 1
Exotherm
Peak 2
~20 H
2
O/SO
3
−
~ 6H
2
O/SO
3
−
153
183
213
243
273
Te m p (K)
FIGURE 3.5
Absorption isotherms of Nafion™.
Absorption isotherm of Nafion (fig. 3.5) could be an effective means to under-
stand the water structure within the ionic polymer. During the absorption of the first
four to five molecules of water per an active site (i.e., SO
), the absorption enthalpy
seems constant. But, with further increase in the water content, the absorption
enthalpy decreases and reaches the saturated limit (fig. 3.6).
This fact could be interpreted as initial water interaction with the counter-ions
(hydration only) and further rearrangement and expansion of the polymer structure
during the expansion of microporous channels within the ionic polymer. The enthalpy
reaches approximately -13 kJ/mol of water (H
3
-
form), which is much less than that
+
