Biomedical Engineering Reference
In-Depth Information
FIGURE 4.121
Woven fabric forms of PAN muscles.
forces. The combination of the van der Waals and double-layer interactions acting
together is usually called the DLVO forces.
Figure 4.121 shows that PAN fibers can be woven into fabric forms and then
activated as sheet-like or smart fabric-like artificial muscles. In this case the PAN
fibers were suitably annealed, cross-linked, and hydrolyzed to become “active.” A
cation-modification process was performed using KOH, NaOH, and LiOH, respec-
tively, for the boiling and alkaline-soaking media. It was found that the PAN fibers,
regardless of whether activated in KOH, NaOH, or LiOH, increased from their initial
length after being activated and soaked in distilled water. Lengths then decreased
after the fibers were soaked in the bases.
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. It should be
noted that the maximum displacement could be determined when conditions were
switched between pure water to acidic conditions. The experimental observation
reveals that the osmotic pressure is of great importance for the contraction/elongation
behavior of PAN. It should be noted that PAN fibers have their capability of changing
effective longitudinal strain more than 100% and their comparable strength to human
muscle. Single microfibers of PAN of 10
m in diameter have shown contrac-
tion/expansion linear strain of over 500% in our laboratories.
µ
4.6.13 F
ORCE
G
ENERATION
WITH
P
H D
IFFERENCE
In this experiment, we were interested in the amount of ions sufficient to shrink the
PAN muscle fiber. A single string of PAN fiber with 6.0-cm length before saponifi-
cation was tested. After each force measurement, the fiber was saturated with 1
M
LiOH and rinsed by a sufficient amount of distilled water. When the fiber reached
equilibrium condition, different concentrations of HCl solution were sprayed on the
fiber for the next measurement until the fiber reached steady state. For force mea-
surement, a 30-g load cell (transducer techniques) was used.
