Hybrid Actuation in Coupled Ionic / Conducting Polymer Devices
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Hybrid Actuation in Coupled Ionic / Conducting Polymer Devices Matthew D. Bennett and Dr. Donald J. Leo Center for Intelligent Material Systems and Structures Department of Mechanical Engineering Virginia Tech 310 Durham Hall Blacksburg, VA 24061, USA ABSTRACT Ionic polymer membrane actuators represent a relatively new and exciting entry into the field of smart materials. Several key limitations of these transducers have prevented them from experiencing widespread use, however. For example, the bandwidth of these devices is limited at very low frequencies by characteristic relaxation and at high frequencies by the low elastic modulus of the polymer. In this paper, an overview of the initial results of work with hybrid ionic / conducting polymer actuators is presented. These hybrid actuators are devices that combine the electromechanical coupling of ionic polymer actuators and conducting polymer actuators into one coupled device. Initial results show that these hybrid devices have the potential to offer marked advantages over traditional ionic polymer membrane transducers, including increased stress and strain generation and higher actuation bandwidth. Details of the preparation of these devices and performance metrics are presented and comparisons to baseline materials are made. INTRODUCTION The field of electroactive polymers (EAP) has gained increased attention in the past 15 years. There are several different types of EAPs, each with their own advantages and disadvantages. The goal of this work is to show that the respective advantages of ionic and conducting electroactive polymers can be utilized by combining these two types of materials into one coupled device. Ionic polymer transducers, sometimes called ionic polymer-metal composites (IPMCs), operate by cation motion within the polymer. The most common polymer used for these types of transducers is duPont’s Nafion. Nafion polymer consists of a Teflon backbone with pendant side chains terminated with sulfonate groups. These sulfonates form hydrophilic networked clusters in the polymer, allowing Nafion membranes to serve as polymer electrolytes. When swollen with an appropriate solvent, the cations associated with each of the sulfonate groups are mobilized and able to move within this network. However, because there are no mobile anions in the polymer, Nafion membranes will pass only cations. It is this property of these membranes that gives rise to their unique transduction properties. When plated with a conductive metal electrode, Nafion membranes can be made to bend in response to an electrical input or to generate electric charge in response to an imposed deformation. This bending is related to diffusion or reorganization of the mobile cations in the polymer. Another type of polymer that can be used to make an electromechanical actuator is a conducting polymer. Conducting polymers like polypyrrole, polyaniline, and polythiophene are able to act as organic conductors because of the conjugated nature of their polymer backbones.
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These polymers
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