Encapsulated polypyrrole actuators

Conducting polymer-based actuators undergo volumetric changes as they are oxidized or reduced, from which mechanical work can be obtained. Polypyrrole [Q. Pei, O. Inganäs, Advanced Materials 4 (1992) 277; Q. Pei, O. Inganäs, Journal of Physical Chemistry 96 (1992) 10508; E. Smela, O. Inganäs, Q. Pei, I. Lundström, Advanced Materials 5 (1993) 630; E. Smela, O. Inganäs, I. Lundström, Science 268 (1995) 1735; J.D. Madden, S.R. Lafontaine, I.W. Hunter, Proceedings – Micro Machine and Human Science 95, Nagoya, Japan, October 1995] and polyaniline-based actuators have attracted recent interest because of the high forces per cross-sectional area (stress) and relatively large strains generated at low activation voltages; however, with the notable exception of some bilayers, the operation of these actuators has largely been constrained to bulk liquid environments. Operation out of solution is clearly desirable for many potential applications. Linear actuators that contract in length like muscle fibers fully exploit the high forces produced by conducting polymers. Results presented here demonstrate the operation in air of polypyrrole linear actuators. These actuators are capable of generating stresses exceeding those of mammalian skeletal muscle.