Carbon Nanotube/Polyelectrolyte Composites as Novel Actuator Materials
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CARBON NANOTUBE/POLYELECTROLYTE COMPOSITES AS NOVEL ACTUATOR MATERIALS Debjit Chattopadhyay, Izabela Galeska, Ray Baughman1, Anwar Zakhidov1 and Fotios Papadimitrakopoulos∗ Nanomaterials Optoelectronics Laboratory, Department of Chemistry, Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, CT 06269-3136 1 Honeywell Co., 101 Columbia Road, Morristown NJ 07962-102. ABSTRACT Mechanical actuators that simultaneously provide high power densities and large force generation capacities are of great scientific and technological interest. Recently single wall carbon nanotube (SWNT) papers (“bucky” papers) were shown to possess significant promise as electrochemical actuators. Embedding polyelectrolytes, like Nafion, within the nanotube matrix has the potential to address the limitations of SWNT bundling and tube slippage thus increasing force generation. In this paper two types of Nafion/SWNT composite actuators have been investigated depending on the method of fabrication. In the first case, infiltration of Nafion within SWNT paper matrix was followed by annealing at 150 °C to invert Nafion's micellar structure and render it insoluble. This has resulted in a substantially exfoliated layer morphology that causes a reduction in both conductivity and actuation strain (c.a. 0.03%). In the second case, slow casting of a methanolic suspension of Nafion and SWNT soot, followed by annealing at 150 °C, resulted in a more homogeneous structure. This composite, upon electrochemical cycling between -1 and +1 V in aqueous electrolytes, exhibited actuation strains (as high as 0.43%). However, these higher strains are accompanied by an order of magnitude reduction in modulus largely due to Nafion swelling. INTRODUCTION The ever-increasing need for mechanical actuators that simultaneously provide high power densities and large force generation has stimulated considerable interest in the scientific community. Existing technologies such as ferroelectrics, electrostrictives and magnetostrictives requiring high electric or magnetic fields[1] limitting their wide spread applications. Although electroactive polymers address the need for low operating voltages, mechanical and electrochemical fatigue associated with the underlying Faradaic intercalation-deintercalation process limit the rate and life cycles of these devices.[2] Recently single wall carbon nanotube (SWNT) papers (“bucky” papers) were shown to possess significant promise as electrochemical actuators.[3] Their low operating voltage (typically less than a few volts) coupled with their excellent mechanical properties[4, 5] and predicted strains (up to 1% in aqueous electrolytes) represent an important breakthrough in actuator technologies. Another significant advantage of the SWNTs lies in their high electrical conductivity[6], which obviates the need of metallic contacts for actuating devices. The actuation in SWNTs is based on a non-faradaic charge injection process resulting in the formation of a electric double layer at the interface with the ∗
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