Passive mechanical properties of polypyrrole films: a continuum, poroelastic model

Several porous material systems (e.g. hydrogels, conducting polymers, electrorheological solids) make it possible to control their mechanical properties in response to appropriate stimuli. Among various conducting polymers showing electromechanical conversion properties, polypyrrole and polyaniline have been, by far, more extensively investigated in order to realize biomimetic actuation devices. To use conducting polymers in engineering applications, one must be able to measure their mechanical properties and predict their static and dynamic response. In this paper we experimentally investigate the passive mechanical properties of a polypyrrole thin film saturated by a fluid. Then, we utilize poroelastic theory to describe the passive mechanical behavior of a conducting polymer film immersed into an aqueous solution. The model we propose is evaluated in the case of a stress-relaxation experiment and under the condition of “free swelling”. The goodness of fit between experimental and theoretical data confirms the validity of the model which ascribes short-time relaxation behavior of wet polypyrrole to solid polymer viscoelasticity and long-time relaxation to polymer-solvent interaction.