Biomedical Engineering Reference
In-Depth Information
∞
∑
(
)
2
∆
∆
l
l
8
21
21
n
+
t
=−
1
exp
−
(4.2)
(
)
2
2
τ
n
+
π
0
n
=
0
where the characteristic time,
τ
, is given by
2
4
l
(4.3)
ch
τ
=
2
π
D
where
l
ch
is the characteristic length (i.e., fibril diameter) and
D
is the overall diffusion
coefficient of ions within the PAN-N fibers. The implication of this equation is that
the contraction or elongation kinetics should be dependent upon the length scale
(i.e., nanofiber diameter), as we have observed experimentally. Therefore, the impor-
tance of our effort to fabricate PAN nanofibers can be realized.
4.6.6
E
XPERIMENT
The polymer solution used in the present electrospinning experiments was prepared
using PAN purchased from Scientific Polymer Products. The electrospinning appa-
ratus used a variable high-voltage power supply purchased from Gamma High
Voltage Research. A 20-ml glass syringe with a Becton Dickinson 18 hypodermic
needle was tilted at approximately 5 degrees from horizontal so that a small drop
was maintained at the capillary tip due to the surface tension of the solution. The
tip of the needle was filed to produce a flat tip.
O
N
O
N
O
C
O
C
C
C
OH
N
N
O
Li
+
Li
+
HO
Li
+
O
O
O
N
N
C
C
Li
+
O
OH
10?0
µ
m
50
µ
m
50
µ
m
FIGURE 4.78
PAN elongation behavior explained by the osmotic behavior and PAN fibers
in different states. Top left: neutral state; top right: under alkaline solutions. Therefore, if pure
water is in contact with alkaline PAN, there will be an osmotic pressure driven water influx.
Bottom left: oxidized PANs (prior to activation); bottom middle: at low pH, contracted PAN
(1
N
HCl); bottom right: at high pH, expanded PAN (1
N
LiOH).
