In-situ Measurement of Actuation in Thin Films of Conducting Polymers
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1222-DD03-02
In-situ Measurement of Actuation in Thin Films of Conducting Polymers Lauren C. Montemayor1, Priam V. Pillai1, Ian W. Hunter1 1 Bio-Instrumentation Laboratory, Massachusetts Institute of Technology, Mechanical Engineering, 77 Massachusetts Avenue, Cambridge, MA 02139, U.S.A. ABSTRACT Conducting polymer materials can be developed as muscle-like actuators for applications in robotics, micro-electro mechanical systems, drug delivery systems etc. These materials are available in a large number of different varieties that can be synthesized and processed in different ways. However, their applications as actuators are limited due to the inability to create conducting polymer materials with robust mechanical properties. Currently most of the dynamic mechanical analysis technologies require the polymer created to be free standing and able to withstand large stresses. This severely limits the development of new materials with potential actuator applications. In this study, a technique to measure the actuation of polymers in the electrochemical deposition environment is described. This allows testing of an electrochemically grown conducting polymer sample on the surface of the deposition electrode itself. Thin polypyrrole films (2 to 20 microns thick) doped with tetraethylammonium hexaflourophosphate were grown on the surface of a glassy carbon electrode. These films were then tested on the surface of the glassy carbon using a custom built electrochemical dynamic mechanical analyzer. A square wave potential (+/- 0.8 V) is applied to the films that results in the actuation of the films. The films are able to generate a changing force of 3 mN of force against a 0.1 N sensor preloaded at 5 mN. The resulting magnitude of the measured force is a function of the film thickness while the change in force due to actuation is approximately constant. INTRODUCTION Materials capable of actuation in the presence of electrochemical cycling, such as conducting polymers (CP), have enormous potential to be used in applications requiring musclelike actuators [1-5]. Actuators with these capabilities can be used to generate movement in various environments, such as robotic and micro-electro mechanical systems. In the case of thin films of CP, actuation occurs when these films are placed in a solution containing specific ions and exposed to a varying potential. As a result of this electrochemical cycling, ions move in and out of the material causing the film to expand and contract. This type of behavior provides the conducting polymer films with the capability to be used in systems where the integration of moving mechanical parts, to provide the necessary actuation, can be cumbersome. Current actuation verification techniques in the development of CPs require that the electrodeposited thin films have robust material properties. They have to be robust enough so that they can be removed from the deposition surface (free-standing) which severely limits the different types of films that can be tested [6]. However, a few researchers have
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