Development of polypyrrole-based electromechanical actuators

The development of practical actuators based on conducting polymers having a force capacity of several tens of kilograms is considered by evaluating the stress generated by different actuator designs. Large, free-standing polypyrrole (PPy) films give a force density well below the theoretical maximum due to the inherent electrical resistance of the film. This may be overcome by applying a metallic coating, but this is best achieved by applying the conducting polymer as a coating on a metallised polymer substrate. Increased electrical resistance (and, hence, reduced actuator performance) was also observed when the film thickness was increased and when gel electrolytes were used. The limitations on actuator performance due to ion diffusion kinetics were illustrated by studies on the effects of scan rate. The most suitable design for scale-up to practical actuator devices was based on a bundled fibre arrangement where the PPy was first coated onto Pt-coated polyester fibres. This design produced the highest stress achieved to date.