**1. Introduction**

158 Electropolymerization

Zhao, H.; Li, L.; Yang, J. & Zhang, Y. (2008a). Nanostructured polypyrrole/carbon

Zhao, H.; Li, L.; Yang, J.; Zhang, Y. & Li, H. (2008b). Synthesis and characterization of

Zhao, H.; Yang, J.; Li, L.; Li, H.; Wang, J. & Zhang, Y. (2009). Effect of over-oxidation

Zhou, Q.; Li, C. M.; Li, J.; Cui, X. & Gervasio, D. (2007). Template-Synthesized Cobalt

*Int. J. Hydrogen Energy,* Vol. 34, No.9, pp. 3908–3914, ISSN 0360-3199 Zhao, S.; Zhang, G.; Fu, L.; Liu, L.; Fang, X. & Yang, F. (2011). Enhanced Electrocatalytic

No.2, pp. 375–380, ISSN 0378-7753

ISSN 1521-4109

ISSN 1932-7455

*Commun.*, Vol.10, No.6, pp. 876–879, ISSN 1388-2481

composite as Pt catalyst support for fuel cell applications. *J. Power Sources*, Vol.184,

bimetallic Pt–Fe/polypyrrole–carbon catalyst as DMFC anode catalyst. *Electrochem.* 

treatment of Pt–Co/polypyrrole-carbon nanotube catalysts on methanol oxidation.

Performance of Anthraquinonemonosulfonate-Doped Polypyrrole Composite: Electroanalysis for the Specific Roles of Anthraquinone Derivative and Polypyrrole Layer on Oxygen Reduction Reaction. *Electroanalysis*, Vol.23, No.2, pp. 355-363,

Porphyrin/Polypyrrole Nanocomposite and Its Electrocatalysis for Oxygen Reduction in Neutral Medium. *J. Phys. Chem. C*, Vol.111, No.30, pp. 11216-11222, Organic soft actuators attract strong attentions because they have many advantages compared to conventional mechanical actuators. Organic soft actuators are generally light and flexibly deformed. In addition, they operate under low voltage ranges as low as 1 volt or so, and generate no sound during deformation. Amongst those soft actuators, bending soft actuators are of special interest because small volume change in organic materials can cause a large bending displacement. For example, soft actuators consisting of Ionic Conducting Polymer Films (ICPF) have been widely used as bending actuators (Guo et al., 1996). However, the fabrication processes for ICPF actuators seem complicated. In contrast, polypyrrole films synthesized using electropolymerization as a new material for organic soft actuators have been extensively studied (Hara et al., 2004a, 2004b, Hatchison et al., 2000, Jager et al., 1999). In addition, the amount of the volume change can be modified by altering the electropolymerization conditions. Hara et. al. recently reported that the expansion and contraction ratio of their polypyrrole actuators exceeded 40%, which is very encouraging (Hara et al., 2005). Bending actuators can be easily fabricated by forming a bimorph structure consisting of a polypyrrole film and other film material.

 In this section, simple bimorph actuators using an electropolymerized polypyrrole (PPy) film and a both-side adhesive tape were fabricated. It turned out that those actuators nonuniformly bent depending on the distance between the actuator and the counter electrode. We fabricated a structure consisting of polypyrrole/both-side adhesive tape/polypyrrole whose two polypyrrole films have different extension/contraction ratios, and found that the actuator exhibited more uniform bending deformation which was nearly independent of the distance between the electrodes.

#### **1.1 Principle of PPy actuator**

Figure 1.1. describes the principle of the PPy actuator functions. A PPy actuator and a counter electrode are placed in an electrolysis solution. When a negative voltage is applied to the actuator, negative ions in the solution will be driven out from the actuator, the actuator shrinks. This is called dedoping process. When positive voltage is applied to the actuator, the negative ions are absorbed into the PPy actuator (doping process), and the actuator expands. The conductive PPy polymer networks are loosely dangled, and the spacing between the polymer chains can expand and shrink during the doping and dedoping processes.

Polypyrrole Soft Actuators 161

conditions. The thicknesses of the PPy films were measured using a micrometer. Three samples of PPy1(68.8 m)/adhesive tape, PPy1(138.8 m)/adhesive tape, and PPy1(138.8 m)/adhesive tape/PPy2(28.6 m) were fabricated. The PPy film and the adhesive tape film were stacked together. The stacked structure was cut to form actuators with the appropriate size. The area of the samples investigated here was 5×20 mm2. The adhesive tape used here

The bending experiments for the fabricated devices were performed using the same experimental setup for the PPy polymerization as shown in Fig. 1.2. Here, the potentiostat HZ-5000, Hokuto Denko Corp. was also used to perform the actuation experiments. The top part of the PPy actuator was connected to the working electrode using a metal clip to make the electrical contact. Then, the counter electrode, the reference electrode, and the the actuator were immersed in a water solution of an electrolyte, lithium bis-trifluoromethane sulphonyl imide (LiTFSI). A bias voltage was given at the working electrode during the bending experiments. The bias ranges was -1.0~+1.0 V, and the bias sweep rate was 10 mV/s. Please note that only the lower part of the actuator was immersed in the LiTFSI

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

solution, and that the conducting PPy actuator acts as the working electrode.

electrode shows a curl, and the actuator bending was not uniform.

is a both-side adhesive tape (NW-10S) produced by Nichiban Inc.

Fig. 1.2. Setup for Galvanostatic electropolymerization.

**1.2.2 Actuator characterizations** 

**1.2.3 Results and discussions** 

Fig. 1.1. The conceptual description of principle for the expansion and contraction processes of PPy actuators.

### **1.2 Experimentals**

#### **1.2.1 Galvanostatic electropolymerization of pyrrole**

Figure 1.2. describes the experimental setup for the Galvanostatic electropolymerization to form PPy films. A counter electrode (Ti), a reference electrode (Ag/AgCl), and a working electrode (Ti) were immersed into a solvent containing pyrrole monomers and an electrolyte, and the bias voltage was controlled to keep constant current between the counter electrode and the working electrode during the PPy polymerization. The PPy film deposited on the working electrode was peeled off, and was used as an actuator material. The characteristics of PPy polymers had very different characteristics influenced by different synthetic conditions of the galvanostatic electropolymerization. For example, if different electrolytes were used, the expansion contraction ratios were very different (Han et al., 2004). The polymerization was done using a computer controlled potentiostat (HZ-5000, Hokuto Denko Corp.).

Here, PPy films with different expansion/contraction behaviors were prepared under different fabrication conditions (PPy1 and PPy2) listed below.


Here, two films with the thickness of 68.8 m and 138.8 m were prepared under the PPy1 conditions, and a film with the thickness of 28.6 m was prepared under the PPy2

**PPy actuator Counter electrode** 

Fig. 1.1. The conceptual description of principle for the expansion and contraction processes

**Dopants Electrolyte solution** 

**(a) (b)** 

Figure 1.2. describes the experimental setup for the Galvanostatic electropolymerization to form PPy films. A counter electrode (Ti), a reference electrode (Ag/AgCl), and a working electrode (Ti) were immersed into a solvent containing pyrrole monomers and an electrolyte, and the bias voltage was controlled to keep constant current between the counter electrode and the working electrode during the PPy polymerization. The PPy film deposited on the working electrode was peeled off, and was used as an actuator material. The characteristics of PPy polymers had very different characteristics influenced by different synthetic conditions of the galvanostatic electropolymerization. For example, if different electrolytes were used, the expansion contraction ratios were very different (Han et al., 2004). The polymerization was done using a computer controlled potentiostat (HZ-5000,

Here, PPy films with different expansion/contraction behaviors were prepared under

a. PPy1; Electrolyte: N.N-Diethyl-N-methyl-N-(2-methoxyethyl) ammoniumbis (trifluoro methane slfonyl) imide, Solvent: Methyl Benzoate, Room temperature, Current: 0.55

b. PPy2; Electrolyte: tetra-*n*-butylammonium trifluoromethanesulfonate (TBACF3SO3), Solvent: Methyl Benzoate, Room temperature, Current: 0.50 mA/cm2, Deposition time:

Here, two films with the thickness of 68.8 m and 138.8 m were prepared under the PPy1 conditions, and a film with the thickness of 28.6 m was prepared under the PPy2

of PPy actuators.

**1.2 Experimentals** 

Hokuto Denko Corp.).

2hrs)

**1.2.1 Galvanostatic electropolymerization of pyrrole** 

different fabrication conditions (PPy1 and PPy2) listed below.

mA/cm2, Deposition time: 4hrs)

conditions. The thicknesses of the PPy films were measured using a micrometer. Three samples of PPy1(68.8 m)/adhesive tape, PPy1(138.8 m)/adhesive tape, and PPy1(138.8 m)/adhesive tape/PPy2(28.6 m) were fabricated. The PPy film and the adhesive tape film were stacked together. The stacked structure was cut to form actuators with the appropriate size. The area of the samples investigated here was 5×20 mm2. The adhesive tape used here is a both-side adhesive tape (NW-10S) produced by Nichiban Inc.

Fig. 1.2. Setup for Galvanostatic electropolymerization.
