Stimuli-Responsive Macromolecular Composites: Enhanced Stress Modulation in Polypyrrole with Redox-Active Dopants

Structure and conformation of conducting polymer (CP) films have been widely investigated to understand the variation in electrical, chemical, and mechanical properties in different electrochemical environments. The pH-dependent stress response in films of polypyrrole (pPy) doped with three bulky dianionic dopants (indigo carmine (IC), anthraquinone disulfonate (AQ), and naphthalene disulfonate (NP)) were studied using the multibeam optical stress sensor (MOSS) technique. Based on combined current, stress, and mass analysis, a mechanism of mixed ion dynamics is proposed that explains the electro-chemomechanical behavior of these polymers. By changing the pH of the electrolyte from neutral to acidic, a modulation of the stress response (Delta Stress) of these polymers is observed, which was found to be the largest in pPy[IC] (80% decrease) compared to related structural analogues, pPy[AQ] (33%) and pPy[NP] (30%). The decrease in stress response for pPy[IC] and pPy[AQ] is attributed to the simultaneous and opposing motion of charge compensating mobile ions induced by redox activity of the quinone moiety in both IC and AQ, A secondary contributor to stress modulation in pPy[IC] arises from the conformational flexibility of the dopant molecule (IC), which translates into macromolecular flexibility of the polymer composite. The polymeric host (pPy) serves to amplify and propagate the conformation changes of IC.