Biomedical Engineering Reference
In-Depth Information
FIGURE 4.6
Isoionic test fixture shown with a 25-fiber bundle PAN muscle.
4.3.3
PAN S
M
' C
M
YNTHETIC
USCLES
APABILITY
EASUREMENTS
Initial evaluation was performed for the linear strain capability of the PAN muscles
under no applied load. Both regular PAN and nano-PAN exhibited large strain
generation capabilities. Their linear strain capability was approximately 80 and 45%
for the regular PAN muscles and the nano-PAN muscles, respectively (between 1
N
HCl and 1
NaOH). A total 10 cycles were carried out. The regular PAN showed
nearly no degradation in performance. However, the nano-PAN fibers showed sig-
nificant reduction in their performance. At the end of 10 cycles, only 20% strain
generation capability was observed. Also, the structural deformation was observed
for the nano-PANs.
N
4.3.3.1
SEM Studies
Figures 4.7, 4.8, and 4.9 show annealed (cross-linked) PAN before activation. The
process condition was heated at 210
°
C for 75 min. Note that the PAN fiber diameter
is approximately 7
m. Also, the surface morphology shows somewhat structured
textures that are believed to be the consequence of polymeric cyclic macromolecular
reconfiguration with attendant dehydrogenation. However, it can be expected that
more close-chain systems may be achieved at higher temperatures.
Figures 4.10, 4.11, 4.12, and 4.13 show activated PANs at low-pH conditions
µ
HCl) after 10 cycles. It can be seen that, under such a condition, the activated
PANs show a somewhat larger diameter, ~8
(1
N
m, than that of annealed and cross-
linked PANs. This could be due to the electrostatic force existing within the polymer
network after the activation (ionic nature). Another interesting fact is the changes in
the surface textures (see figs. 4.9 and 4.12). In addition, some fibers stick together,
as shown in figure 4.13.
In figures 4.14 and 4.15, the micrographs of activated PANs at a high pH
condition (1
µ
NaOH) are shown. In these figures, the PAN fibers appear to be
covered by salts (i.e., NaOH) but maintain their shape very well. Figures 4.16 and
4.17 clearly show that pilled-off close-up micrographs of the PAN fibers indicate
that inner fiber (i.e., PAN) looks very clean with no visible damage. Figure 4.18
shows a single fiber having a diameter of approximately 9
N
µ
m. The surface is very
