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Proceedings Paper

Potential profile in a conducting polymer strip
Author(s): Lasse Bay; Keld West; Nicolaos Vlachopoulos; Steen Skaarup
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Paper Abstract

Many conjugated polymers show an appreciable difference in volume between their oxidized and reduced forms. This property can be utilized in soft electrochemically driven actuators, "artificial muscles". Several geometries have been proposed for the conversion of the volume expansion into useful mechanical work. In a particularly simple geometry, the length change of polymer strips is exploited. The polymer strips are connected to the driving circuit at the end of the strip that is attached to the support of the device. The other end of the strip is connected to the load. The advantage of this set-up is simplicity and that the maximum force generated in the polymer can be transferred directly to the load. There is, however, an inherent problem in this design that will be examined in this paper. If the potential of the reduced state is below that for oxygen reduction, only a finite length of the free-standing film will be fully reduced. This is due to the reduction of oxygen at the surface of the polymer competing with the reduction of the polymer. For a long strip, the potential will therefore approach the reduction potential of oxygen. This will lower the efficiency of the artificial muscles and complicate measurements on free-standing films. A model of the potential profile in a free-standing strip is derived. It is found that the active length (the length with a given potential change) of the polymer will scale as &sqrt;dσ/id. (d is the thickness, σ the conductivity of the film, and id the diffusion limited current density for oxygen reduction). The active length is typically of the order of millimeters. The model is compared with measurements on a strip of polypyrrole doped with dodecylbenzene sulfonate.

Paper Details

Date Published: 16 July 2001
PDF: 5 pages
Proc. SPIE 4329, Smart Structures and Materials 2001: Electroactive Polymer Actuators and Devices, (16 July 2001); doi: 10.1117/12.432690
Show Author Affiliations
Lasse Bay, Technical Univ. of Denmark (Denmark)
Keld West, Risoe National Lab. (Denmark)
Nicolaos Vlachopoulos, Technical Univ. of Denmark (Denmark)
Steen Skaarup, Technical Univ. of Denmark (Denmark)

Published in SPIE Proceedings Vol. 4329:
Smart Structures and Materials 2001: Electroactive Polymer Actuators and Devices
Yoseph Bar-Cohen, Editor(s)

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