Biomedical Engineering Reference
In-Depth Information
(A)
(B)
FIGURE 13.20
Micrograph (A) shows curving bimorph of polypyrrole nanowires (on top) and Au fi lm (on
the bottom). The bimorph was attached on the left to a substrate, and polypyrrole was oxidized (
V
versus Ag/
AgCl
=
0 V) in NaDBS electrolyte, contracting the nanowires and curving the bimorph upward. Image (B)
shows the same bimorph with swelled polypyrrole nanowires in an electrochemically reduced state (
V
versus
Ag/AgCl
= −
1 V). The scale bars represent 50 µm.
(A)
(B)
4
0.035
3
0.03
2
0.025
1
0.02
0
0.015
−
1
0.01
−
2
0.005
−
3
0
−
4
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0.0
0.1
−
−
−
−
−
−
−
−
1.1
−
1.0
−
0.9
−
0.8
−
0.7
−
0.6
−
0.5
−
0.4
−
0.3
−
0.2
−
0.1
V
versus Ag / AgCl
V
versus Ag / AgCl
FIGURE 13.21
(A) Expansion of polypyrrole nanowires is shown as a function of voltage, starting with
polypyrrole in an oxidized state and applying a voltage from
−
0.2 to
−
1.2 V versus the reference electrode.
Original length of the nanowires
L
=
43 µm. The inset is an optical micrograph of the cross-section of the
sample. The scale bar represents 50 µm. (B) A cyclic voltammetry of the same sample is shown, where an
oxidation peak at
−
0.3 V and split reduction peaks at
−
0.61 and
−
0.73 V can be seen.
The actuation was carried out as above, and the opposing gold fi lms were seen to move apart by
∼
1 V and then move back to
the original position upon oxidation at 0 V. The setup was put through more than 20 cycles, and the
magnitude of expansion or contraction remained the same. Cyclic voltammetry curve for the sample
used in this experiment is shown in Figure 13.21B with prominent oxidation and reduction peaks.
1.3 µm when the nanowires (43 µm long originally) were reduced at
−
13.4.2.4
Discussion of Optical Microscopy and Cyclic Voltammetry Data
There is a strong correlation between the electrochemical behavior of the PPy nanowires and the
observed lengthwise expansion. When a negative reducing voltage is applied to an oxidized PPy,
