Artificial Muscles Based on Polypyrrole Actuators with Large Strain and Stress Induced Electrically

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 (TBABF4) on Ti electrode, exhibited 12.4 % strain and 22 MPa stress generated electrochemically in NaPF6 aqueous solution. The large electrochemical strain and stress of BF4−-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 CF3SO3−-doped PPy films were more suitable than BF4−-doped PPy.