Soft Mechanical Sensors through Reverse Actuation in Polypyrrole

The phenomenon of voltage generated from a soft sensor using polypyrrole in response to mechanical deformation is describedand investigated. The sensor consists of two polypyrrole layers in contact with an electrolyte and operates in bending mode inair. The magnitude and sign of the induced voltage was found to depend on the type of dopant counter-ions and the nature ofthe surrounding electrolyte. The mechanical sensor response is shown to be a reverse actuation, generating millivolt signalsfor millimeter sized deflections or < 1000 Cm3 charge for 1% strain in the polypyrrole layer. A model based on DeformationInduced Ion Flux has been proposed whereby the strain induced volume change in the polymer produces a shift in the Donnanequilibrium between mobile dopant ions inside the polymer and in the external electrolyte. A simple thermodynamic modelprovides reasonable estimates of the size of the voltage and charge produced.