Actuation behaviour of polyaniline films and tubes prepared by the phase inversion technique
The phase inversion technique was used to produce polyaniline (PAn) actuators with film and tube geometries. PAn dissolved in N,N-dimethyl propylene urea was cast, and then coagulated in a water bath forming films and tubes with and without a platinum (Pt) wire helix as an interconnect. The solid PAn was doped with hydrochloric acid solution (1 M HCl) (PAn/HCl) or methanesulfonic acid (1 M MSA) (PAn/MSA). The actuation strain was observed in different electrolytes using constant current stimulation at a frequency of 1 pulse per minute. In nitric acid (1 M HNO3) electrolyte, the actuation strain produced by the PAn/HCl film was 0.9%. The strain increased to 2.0% and 2.7% when the actuator geometry was changed to tube, then to tube with a Pt helix, respectively. Compared to 1 M NaNO3 electrolyte, the use of 1 M HNO3 electrolyte gave better actuation stability, where more than 100 cycles were observed. Changing the coagulation bath from water to NMP (30% w/w)/water resulted in a subtle difference in the Young's modulus of PAn/MSA in the oxidized and reduced states. PAn prepared by the phase inversion technique was porous by nature; consequently it is brittle and exhibits a low actuation stress (400 kPa).