ABSTRACT:Conducting polymer actuators have been attracting researchers and engineers who need powerful and light actuators because of their electrically induced stress (3-5 MPa), 10 times larger than that (0.35 MPa) of vertebrate muscle fibres. The moderate electrically generated strain (1-3 %) has however been restricting their applications to robots, for instance, and therefore relatively huge and heavy electric motors have been inevitably used in the robotic industry. A polypyrrole (PPy) film, which was prepared electrochemically from methyl benzoate solution of tetra-n-butylammonium tetrafluoroborate (TBABF 4 ) on Ti electrode, exhibited 12.4 % strain and 22 MPa stress generated electrochemically in NaPF 6 aqueous solution. The large electrochemical strain and stress of BF 4 À -doped PPy should meet applications of artificial muscles particularly where strong force is required. These novel conducting polymer actuators could dramatically alter any technologies concerning movements. Besides fundamental properties of the PPy actuators, some newly-devised configurations of the actuators for practical use are important. In order to fabricate actuator devices particularly where multiple layers of PPy films were required to increase force, flexible and tough CF 3 SO 3 À -doped PPy films were more suitable than BF 4 À -doped PPy.
KEY WORDSConducting Polymer Actuator / Electroactive Polymer / Artificial Muscle / Polypyrrole / Electrochemomechanical Deformation / Electrochemical Strain / Electrochemical Stress / Electroactive polymer (EAP) actuators are roughly divided into two categories based on their activation mechanism: electronic and ionic.1,2 Of electronic EAP actuators driven by electric field, electroelastomers or dielectric elastomers with up to 380 % strain developed by SRI International have attracted those who need powerful and speedy actuaors.3,4 Dielectric EAPs having low elastic stiffness and high dielectric constant actuate massively in an electrostatic field, and the higher electrostatic field induces larger force and strain of dielectric EAP. The disadvantage of the electronic EAP actuators is, without any doubt, their very high drive voltage of 1000-5000 V.2-5 On the other hand, ionic EAP actuators such as ionic polymer gels (IPGs), 6,7 ionomeric polymer-metal composites (IPMCs), 8,9 and conducting polymers (CPs) 10-13 can be operational under much milder conditions: pH change, temperature control, or low drive voltage (1-2 V), and thus suitable for portable, mobile, small, and simple actuator devices as artificial muscles; for instance, robots, powered suits, artificial limbs, medical devices, and replacement of conventional electric motors. When actuator devices are designed by using EAP materials, only CP actuators are realistic choice because of their large stress generated electrically, 2-3 orders of magnitude larger than that of IPGs and IPMCs. The moderate strain (1-3 %) of CP actuators has however been disappointing those who are in need of artificial muscles. Once the electrochemical strai...
