Conducting polymers are simultaneous sensing actuators

Abstract

Conducting polymers are soft, wet and reactive gels capable of mimicking biological functions. They are the electrochemomechanical actuators having the ability to sense the surrounding variables simultaneously. The sensing and actuating signals are sent/received back through the same two connecting wires in these materials. The sensing ability is a general property of all conducting polymers arises from the unique electrochemical reaction taking place in them. This sensing ability is verified for two different conducting polymers here – for an electrochemically generated polypyrrole triple layer bending actuator exchanging cations and for a chemically generated polytoluidine linear actuator exchanging anions. The configuration of the polypyrrole actuator device corresponds to polypyrrole-dodecyl benzene sulfonate (pPy-DBS) film/tape/ pPy-DBS film in which the film on one side of the triple layer is acted as anode and the film on the other side acted as cathode simultaneously, and the films interchanged their role when move in the opposite direction. The polytoluidine linear actuator was fabricated using a hydrgel microfiber through in situ chemical polymerization. The sensing characteristics of these two actuators were studied as a function of their working conditions: applied current, electrolyte concentration and temperature in aqueous electrolytes. The chronopotentiometric responses were studied by applying square electrical currents for a specified time. For the pPy actuator it was set to produce angular movement of ± 45° by the free end of the actuator, consuming constant charges of 60 mC. In both the actuators the evolution of the muscle potential along the electrical current cycle was found to be a function of chemical and physical variables acting on the polymer reaction rates: electrolyte concentration, temperature or driving electrical current. The muscle potential evolved decreases with increasing electrolyte concentrations, increasing temperatures or decreasing driving electrical currents. The electrical energy consumed during reaction was a linear function of the working temperature or of the driving electrical current and a double logarithmic function of the electrolyte concentration. Thus, the conducting polymer based actuators exchanging cations or anions during electrical current flow is a sensor of the working physical and chemical conditions which is a general property of all conducting polymers.