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Polypyrrole actuators: modeling and performance

Publication Type:

Conference Paper


Proc. SPIE - Int. Soc. Opt. Eng. (USA), Volume 4329, Newport Beach, CA, USA, p.72 - 83 (2001)



capacitance;conducting polymers;diffusion;electric actuators;electric admittance;electrochemical devices;identification;stress-strain relations;transfer functions;


Conducting polymer actuators generate forces that exceed those of mammalian skeletal muscle by up to two orders of magnitude for a given cross-sectional area, require only a few volts to operate, and are low in cost. However application of conducting polymer actuators is hampered by the lack of a full description of the relationship between load, displacement, voltage and current. In an effort to provide such a model, system identification techniques are employed. Stress-strain tests are performed at constant applied potential to determine polypyrrole stiffness. The admittance transfer function of polypyrrole and the associated electrolyte is measured over the potential range in which polypyrrole is highly conductive. The admittance is well described by treating the polymer as a volumetric capacitance of 8·107 F m-3 whose charging rate is limited by electrolyte resistance and diffusion within polypyrrole. The relationship between strain and charge is investigated, showing that strain is directly proportional to charge via the strain to charge density ratio, α=1·10-10 m3·C-1, at loads of up to 4 MPa. Beyond 4 MPa the strain to charge ratio is time dependent. The admittance models, stress/strain relation and strain to charge relationship are combined to form a full description of polypyrrole electromechanical response. This description predicts that large increases in strain rate and power are obtained through miniaturization, yielding bandwidths in excess of 10 kHz. The model also enables motor designers to optimize polypyrrole actuator geometries for their applications


polypyrrole actuator;conducting polymer;system identification;stiffness;transfer function;volumetric capacitance;motor design;electrochemical coupling;electrolyte resistance;diffusion;strain-to-charge density ratio;admittance model;stress/strain relation;electromechanical response;10 kHz;