Preparation and characterization of monolithic polyaniline–graphite composite actuators

We report here the fabrication and characterization of novel, monolithic electrochemical actuators based on polyaniline (PANI) and a micrometer-sized graphite powder. These PANI–graphite thin films have a graphite-rich layer that renders composite thin film conductive at all redox states. The asymmetric distribution of graphite also allows for a bending movement as the films are subjected to electrochemical oxidation and reduction. The unique asymmetric structure and high conductivity of the films allow the actuators to be operated at lower redox potentials, with larger bending angles and longer life cycles. Our study also shows that most of the bending movements occur during the transition between the emeraldine base and the pernigraniline base. Judging from the CV and from the current generated when the square wave potential is applied, we note that the actuators appear very stable and show no signs of degradation after 50,000 working cycles operated at 1 Hz. The life cycles of these actuators exceed 120,000 cycles (>33.6 h) in a 1.0 M CH3SO3H aqueous solution. As we extend the oxidation potential to greater than 0.8 V, the PANI–graphite thin film starts to degrade with time. These results reveal the optimum conditions under which the actuators should be operated.