Biomedical Engineering Reference
In-Depth Information
Fibers treated with LiOH (see table 4.1 and fig. 4.26) 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 dis-
placement in the lengths occurred using the 2-
N
solutions. The lengths of fibers
treated with NaOH (see table 4.3 and fig. 4.28) were close to the same regardless
of the normality of the solutions.
These findings are important to describe casual pH hysteric behaviors that have
been reported previously. In figure 4.29 the importance of osmotic pressure is
illustrated. It should be noted that the maximum displacement could be determined
when conditions are switched between pure water to acidic conditions.
Note from figure 4.29 that the left molecular structure is in a neutral state while the
right molecular structure is under an alkaline solution. Therefore, if there is pure water
in contact with the alkaline PAN, there will be an osmotic pressure-driven water influx.
Again note from figure 4.31 that this configuration provides the membrane elec-
trode functioning as a cathode and the thin conducting wire in a helical spring from
being an anode shedding H+. It can cause the PAN fiber to contract within the helically
configured wire and flexible membrane and the wire will also contract like a helical
spring with the PAN fiber. Once the polarity is changed, the PAN fiber tends to expand
and the compressed helical spring will help it expand in a resilient manner.
4.3.7
A
DDITIONAL
E
XPERIMENTAL
R
ESULTS
C for 2 h. They were then boiled for 30
min in either 1
N
NaOH or 1
N
LiOH and stored in 1
N
HCl. An apparatus was set
up (see fig. 4.32) composed of a stainless steel anode, a spring (serving as a counter-
electrode) with one PAN fiber attached to it, a beaker filled with 150 mL of electrolyte
solution, and a 25-amp Midas
®
Rectifier, which supplied the voltage. The electrolyte
solution was either 0.1
N
NaCl or 0.1
N
LiOH, depending on the experiment.
The stainless steel anode was attached to the negative lead and held upright in
the beaker of solution using a clamp. The spring with the fiber attached to the inside
of it was attached to the positive lead. After the fiber and spring had been immersed
in solution, the fiber was measured to see whether it had expanded at all. The spring
PAN fibers were temperature treated at 230
°
FIGURE 4.32
Photographs of experimental setup.
