The Effect of Temperature Exposure on Polypyrrole Actuation

Abstract

Polypyrrole actuators offer attractive possibilities due to their large electrochemical stress (<5MPa), moderate to large strain (<2 %) and low voltage operation (<2 V). However, little is known about their temperature dependence response, with nearly all previous tests performed at room temperature. To test the effects of increasing temperature, polypyrrole films in water and propylene carbonate were thermally cycled twice from 22°C to 80°C. Length and actuation were measured before, after and between cycling. Results show that polypyrrole in TBAPF_{6(propylene carbonate)} underwent a 4.8% irrecoverable contraction during the first cycle and lost half it’s actuation each cycle. Polypyrrole in NaPF_6(aq) showed a 2.1% initial expansion in length on the first cycle followed by a 2.1% contraction on the next cycle, while active strain amplitude dropped from 7.7% to 5.9% to 4.9%. Polypyrrole in NaCl_(aq) has a net contraction of 6% over two cycles with no significant change in it’s original 3.5% actuation amplitude. This suggests that although films in NaPF_6(aq) have the best initial strain, films in NaCl_(aq) maintain the most consistent strain amplitude in response to temperature on the timescales observed. Strain to charge ratio was found to decrease slightly, but the majority of the loss in actuation for films is correlated with a reduction in charge transfer each cycle. This reduction may result from a reduction in the active volume of film.