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 described

and investigated. The sensor consists of two polypyrrole layers in contact with an electrolyte and operates in bending mode in

air. The magnitude and sign of the induced voltage was found to depend on the type of dopant counter-ions and the nature of

the surrounding electrolyte. The mechanical sensor response is shown to be a reverse actuation, generating millivolt signals

for millimeter sized deflections or < 1000 Cm3 charge for 1% strain in the polypyrrole layer. A model based on Deformation

Induced Ion Flux has been proposed whereby the strain induced volume change in the polymer produces a shift in the Donnan

equilibrium between mobile dopant ions inside the polymer and in the external electrolyte. A simple thermodynamic model

provides reasonable estimates of the size of the voltage and charge produced.