Thermo-mechanical characterization of polypyrrole compliance using stochastic system identification

Conducting polymers such as polypyrrole are studied as novel biologically inspired actuators. Their capacity to generate stresses of up to 5 MPa, strains of up to 10% at low voltages (2 V) make them ideal candidates to be used as artificial muscle materials. It has been shown that the modulus of polypyrrole can change when the material is electrochemically excited. In this paper we develop a technique that uses a stochastic stress input that can be used to measure the compliance frequency response (between 10^-2 Hz and 100 Hz) of polypyrrole in-situ. We validate the compliance calculated from the stochastic stress input by comparing it with the compliance calculated from a single sinusoidal stress input. We also measure the compliance as a function of temperature using both techniques and show that the stochastic compliance follows the same trends as the compliance calculated from single sinusoidal stress input.