Ionic Polyacrylonitrile Chemoelectromechanical Artificial Muscles/Nanomuscles - Artificial Muscles - page 204

FIGURE 4.122 Electrochemical test setup.
Figure 4.122 shows the experiment's apparatus. In the first experiment, there is
a step in force generation because of discontinuation of HCl supply. The maximum
forces of PAN fiber in response to each concentration of HCl solution, which were
2.15 g for 0.01 M , 2.66 g for 0.1 M , 2.71 g for 0.5 M , 3.1 g for 1 M , and 2 M =
2.84 g, were measured. There was 1-g force gap between 0.01- and 0.1- M solution,
and when the concentration of solution was low, there was a time delay to reach the
peak point. In high-concentration solution, such as 1 and 2 M , the force reached the
maximum value almost immediately. Even in 0.01- M concentration of HCl, 72% of
force, compared with the force generated in 1- M solution whose concentration is
100 times stronger, was observed.
Another force variation measurement along with pH difference using other acids
such as sulfuric acid and nitric acid was ongoing in order to investigate whether the
anion of acid solution affects the test result. The results of these experiments are
depicted in figures 4.123a and 4.123b, as well as figures 4.124a, 4.124b, and 4.125.
In order to achieve kinetic energy, a PAN actuating system or a PAN muscle system
depends on pH change of its environment. In an electrically controlled PAN muscle
system, localized pH difference during the water electrolysis is the key parameter that
actually makes the movement of PAN fiber. To reduce the response time, applying a
diaphragm (ion-separation materials) between anode and cathode electrode was con-
sidered. Ionic diaphragms prevent ion transportation, which will increase concentration
of ions rapidly and reduce the response remarkably. Furthermore, note that corrosion
of anode electrodes occurs because H + ions chemically react with copper. The copper
surface has been plated with gold to block direct contact between copper surface and
H + ions. However, the plating is not dense enough to prevent chemical reaction. The
ions penetrate, crack, and corrode copper under the gold layer. To make a denser layer
on the copper surface, use of appropriate plating material such as hexachloroplatinate
(H 2 PtCl 6 ) was also considered and tested.