Asymmetric Bilayer Muscles. Cooperative and Antagonist Actuation

Thick films of polypyrrole-paraphenolsulfonic acid (PPy-HpPS), polypyrrole-dodecylbenzensulfonic acid (PPy-DBS) and a bilayer PPy-HpPS/PPy-DBS (asymmetric bilayer) were electrogenerated from aqueous solutions. Two bilayers: PPy-HpPS/tape and tape/PPyDBS were constructed. The angular displacement of those three bilayer muscles was characterized in NaCl aqueous solution by cyclic voltammetry and parallel video recording of the bending movement. The attained coulo-voltammetric (charge-potential), dynamo-voltammetric (angle-potential) and coulo-dynamic (charge-angle) responses until different cathodic potential limits were analyzed. The dynamo-voltammetric and coulo-dynamic responses from the PPy-HpPS/tape and tape/PPyDBS muscles inform about the reaction driven ionic exchanges in the two PPy films. Electrochemo-dynamical responses from the asymmetric PPy-HpPS/PPy-DBS bilayer muscles are explained using those reactions. Cooperative dynamic effects exist when both layers follow complementary reaction-driven volume changes (swelling/shrinking, or shrinking/swelling) due to complementary entrance/expulsion of ions. The cooperative amplitude of the angle described by the asymmetric bilayer muscle is one order of magnitude larger than those attained from each of the conducting polymer/tape bilayer muscles. Antagonist dynamic actuation occurs when the two films swell, or shrink, simultaneously originating narrower angular displacements. Improving cooperative actuation or eliminating antagonist actuation and creeping by suitable selection of polymers and electrolytes seem the way to get most efficient polymeric motors and industrial products. 2016 The Authors. Published by Elsevier Ltd.