**1.2.3 Results and discussions**

Figure 1.3a and figure 1.3b show the photographs during deformation of the PP1(68.8 m)/adhesion tape actuator. Obviously, the bi-directional bending of the actuator was observed. However, as seen in the Fig. 1.3a, the actuators edge area close to the counter electrode shows a curl, and the actuator bending was not uniform.

Polypyrrole Soft Actuators 163

**PPy1 (counter Bending angle (deg) Total (deg)** 

68.8 None +42.4 -47.8 90.2 138.8 None +11.3 -85.4 96.7 138.8 28.6 +24.3 -23.6 47.9

Table 1. Results of bending angles of the PPy actuators ※ Positive angle means that

Two kinds of polypyrrole films were galvanostatically fabricated, and the polypyrrole/adhesive bending actuators were fabricated. The actuators exhibited a large bending angle range of nearly 90o. However, when the actuators approached the counter electrode, the bending angle increased which resulted in non-uniform bending of the actuators. Then, the three-layered actuator of PPy1/adhesive tape/PPy2, whose PPy films have different expansion/contraction ratios, was fabricated and characterized. The three layered actuator showed pretty uniform bending deformation with some expense of the

PPy actuators have been regarded as a possible candidate for an artificial muscle because the generation of stress is nearly ten times larger than human muscles. However, the expansion and contraction ratio of a PPy actuator was only 1–3 % which was far smaller than the value of human muscle, 25% (Hara et al., 2005, Baughman, 1996). However, Hara et. al. recently reported that an expansion and contraction ratio of their PPy actuators exceeded 40%, which is very encouraging (Hara et al., 2004). There are also several reports to improve the expansion and contraction ratios by modifying PPy film deposition conditions such as temperatures and modifying supporting electrolyte solutions (Hara et al.,

In this section, a new structure of PPy actuators to improve the expansion and contraction ratio is proposed. Here, the details of fabrication procedures and the characterization results

The PPy thin film was fabricated by electropolymerization. The electropolymerization of PPy was done in a methyl benzoate solution with a volume of 50 ml in which pyrrole monomers with a concentration of 0.25 mol dm-3 and the electrolyte (N, N- Diethyl- Nmethyl-N-(2-methoxyethyl) ammonium bis (trifluoromethanesulfonyl) imide with a

The working electrode was a Au thin film sputtered on an acrylic board and the counter electrode was a Ti plate. The area of the electrodes immersed in the solvent was 30×25 mm2. The polymerization was done at a constant current of 0.2 mA cm-2 for 4 hrs at the room temperature. The PPy thin film was polymerized with the doped anions in the supporting

actuators bend towards direction opposite to the counter electrode.

**2. Polypyrrole soft actuator having corrugated structures** 

2005a, 2005b, 2005c, Zama et al., 2005a, 2005b, Ogasawara et al., 1986).

of the corrugated PPy soft actuator are reported.

**2.2.1 Fabrication processes of PPy soft actuator** 

concentration of 0.2 mol dm-3 are dissolved.

**Thickness (m)**

**electrode side) PPy2 (Rear side)** 

**1.3 Conclusion** 

bending angle.

**2.1 Introduction** 

**2.2 Experimentals** 

Fig. 1.3. Bi-directional bending organic actuator of PPy1(68.8 m)/adhesive tape.

This phenomenon may be due to the fact that the electric field between the actuator and the counter electrode increases resulting in the increase of the ionic current when the actuator comes closer to the counter electrode. Therefore, it was considered that some techniques to prevent this phenomenon were necessary. It was considered that if PPy1/adhesive tape/PPy2 with different extension/contraction ratios or different thickness may prevent non-uniform bending of the actuators. Figure 1.4. exhibits the bending characteristics of the PPy1 (138.8 m)/both-side adhesive tape/PPy2 (38.8 m). Note that the actuator shown in Fig. 1.4. shows fairly uniform bending independent of the relative positions from the counter electrodes with some expense of the bending angle.

Fig. 1.4. Bi-directional bending organic actuator of PPy1(138.8 m)/adhesive tape/PPy2(28.6 m).

The experimental results are summarized in Table.1. As seen in Table.1, the bending angle increases when the PPy film thickness increases, and the bending angle can be adjusted by changing the thicknesses of the PPy films on both sides.

The reason for the uniform bending has still not yet been clarified. However, it might be speculated that when a part of the actuator comes closer to the counter electrode, the amount of dopants penetrating into the part will be larger, which may cause the nonuniform bending of the PPy/adhesive actuator. On the other hand, this nonuniform bending may be canceled in the PPy1/adhesive tape/PPy2 structure, because the amounts of the dopants of the PPy1 and the PPy2 films near the counter electrode become larger simultaneously.

(a) (b)

counter electrodes with some expense of the bending angle.

(a) (b)

changing the thicknesses of the PPy films on both sides.

m).

Fig. 1.3. Bi-directional bending organic actuator of PPy1(68.8 m)/adhesive tape.

This phenomenon may be due to the fact that the electric field between the actuator and the counter electrode increases resulting in the increase of the ionic current when the actuator comes closer to the counter electrode. Therefore, it was considered that some techniques to prevent this phenomenon were necessary. It was considered that if PPy1/adhesive tape/PPy2 with different extension/contraction ratios or different thickness may prevent non-uniform bending of the actuators. Figure 1.4. exhibits the bending characteristics of the PPy1 (138.8 m)/both-side adhesive tape/PPy2 (38.8 m). Note that the actuator shown in Fig. 1.4. shows fairly uniform bending independent of the relative positions from the

Fig. 1.4. Bi-directional bending organic actuator of PPy1(138.8 m)/adhesive tape/PPy2(28.6

The experimental results are summarized in Table.1. As seen in Table.1, the bending angle increases when the PPy film thickness increases, and the bending angle can be adjusted by

The reason for the uniform bending has still not yet been clarified. However, it might be speculated that when a part of the actuator comes closer to the counter electrode, the amount of dopants penetrating into the part will be larger, which may cause the nonuniform bending of the PPy/adhesive actuator. On the other hand, this nonuniform bending may be canceled in the PPy1/adhesive tape/PPy2 structure, because the amounts of the dopants of the PPy1 and the PPy2 films near the counter electrode become larger simultaneously.


Table 1. Results of bending angles of the PPy actuators ※ Positive angle means that actuators bend towards direction opposite to the counter electrode.
