Biomedical Engineering Reference
In-Depth Information
250
200
150
100
50
0
−
50
FIGURE 4.82
NMR spectrum of PAN processed fibers.
saponification. Generally speaking, the activated PAN (in wet state) can inherently
carry cation (Na+) and anion groups (pyridine rings/cyano groups).
The PAN nanofibers were suitably annealed, cross-linked, and hydrolyzed to
become “active.” A key molecular structure of PAN—hydrogen bonding between
hydrogen and the neighboring nitrogen of the nitrile group—exhibiting insolubility,
thermal stability, and resistance to swelling in most organic solvents is thought to
be due to its cross-linked polymer structure. These results provide a great potential
in developing fast activating PAN muscles and linear actuators, as well as integrated
pairs of antagonistic muscles and muscle “sarcomeres” and “myosin/actin”-like
assembly with potential interdigitated control capabilities.
First, the effect of different cations (Li
+
, Na
+
, and K
+
) on the contraction/elon-
gation behavior of activated PAN fiber was determined. PAN fibers were tested in
alkaline and acidic solutions of different normalities in order to determine their
optimum contraction and elongation properties. Interestingly, Li
+
-based PAN fibers
exhibited the largest elongation/contraction performance. PAN fibers were oxidized
at 220
C for 90 min in air. In the first experiment, these fibers measured one inch
in length and each was activated in boiling 1
N
KOH for 30 min. The fibers were
then soaked in distilled water for 30 min in order to obtain a base length. Then,
several fibers were placed in each of 0.5, 1, and 2
N
KOH for 30 min and measured.
Next, the fibers were again put into distilled water for 30 min and then measured.
Following this, the fibers were soaked in 0.5-, 1-, and 2-
N
HCl solutions (corre-
sponding fibers from the alkaline, e.g., fibers from the 0.5
N
KOH were placed in
0.5
N
HCl) and measured. Also, this process was repeated using NaOH and LiOH
for the boiling and alkaline-soaking media.
Fibers treated with LiOH had the largest increase in length following immersion
in distilled water. Fibers soaked in all three media generally had the same decrease
in length following immersion in the alkaline solutions, as also occurred following
immersion in HCl. Especially noticeable with the fibers treated with LiOH was that
greater displacement in the lengths occurred using the 2-
N
solutions. The lengths of
fibers treated with NaOH were close to the same regardless of the normality of the
°
