Electro-chemo-mechanical response of a free-standing polypyrrole strip

Abstract

Abstract. Further development of mechanical devices based on conducting polymers; require a precise understanding of their mechanical response, i.e. their control, under a controlled external current. In this work, we show some results for the relation between the electrical current consumed in the electrochemical process and the mechanical work developed by a freestanding polypyrrole strip, when it is subjected to a stretching force (stress). Under these conditions, from the results obtained in this work, we observe how it results almost impossible to predict a straight relationship between mechanical work and current consumed in the electrochemical process. In addition, we will quantify the variation of the mechanical properties of the free standing polypyrrole strip associated with the oxidation state of the polymer by measuring its Young's modulus.

Nanostructural Aspects of Conducting‐Polymer Actuators

“…Part of the explanation for the behavior of conducting-polymer actuators can be related to a change in Young's modulus which occurs as PPy passes through different oxidation states -the elastic modulus tends to decrease as the polymer is reduced leading to a length increase under load, which can work against the contraction in length due to ion and solvent expulsion [35,67] The decrease in modulus for the reduced polymer has been explained as a lowering in interchain interactions, given that strong p-p stacking interactions within the oxidized polymer state lead to a stiffer structure [68]. Other groups have shown how the modulus varies with the applied potential [69], and that the modulus is dominated by the degree of counter-ion swelling for both anions and cations, with an emphasis on how critical the modulus changes will be to the mechanics of devices driven by polypyrrole actuators [70]. Conducting polymers are unusual as artificial muscles in that their work-per-cycle goes through a maximum as the applied stress is increased, again related to the change in modulus which occurs upon oxidation and reduction (by up to 500%) [71].…”