Graphene Electromechanical Actuation; Origins, Optimization and Applications
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Graphene Electromechanical Actuation; Origins, Optimization and Applications Geoffrey W. Rogers1 and Jefferson Z. Liu1 1 Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3800, Australia.
ABSTRACT Graphene-based materials have emerged as exceptional candidates for the development of novel, high performance actuators. Developing such an actuation material requires an in depth knowledge of the physics of operation and, therefrom, how to best optimize its performance. We investigate the electromechanical actuation of pristine monolayer graphene to elucidate the origin of this material’s exceptional electromechanical actuation performance. It is shown that the electrostatic double-layer (EDL) effect is dominant compared to the quantum-mechanical (QM) effect upon charging and electrolyte immersion. Seeking to optimize the QM actuation performance, we preliminarily investigate graphene oxide (GO) as a potential graphene-based actuation material, and find that it exhibits both unique and high performance responses. Having demonstrated huge stresses (~100 GPa) and high strains (~0.4%), graphene-based materials are uniquely positioned to address future industrial actuation challenges. INTRODUCTION Carbon nanotubes (CNTs) and graphene have garnered immense interest throughout the past decade, due to their equally intriguing and novel mechanical, electronic and chemical properties. These unique properties have led many to explore potential applications for these materials, which include nano-electronics [1], quantum computing [2], solar cells [3], desalination [4], supercapacitors [5], GHz nano-mechanical oscillators [6] and electromechanical actuators [7]. In the case of actuation, right from the moment of first report it was evident that the excellent electronic and mechanical properties embodied by these materials provided a recipe for actuator success [7]. Furthermore, many of the other inherent features of these materials, such as their high thermal and chemical stabilities, have paved the way for the potential development of actuators that could be used in previously unserviceable applications. Accordingly, there is much to be gained from the development of CNT and graphene based electromechanical actuators. Following the first demonstration of a CNT actuator [7], many sought to understand the origins of the unique actuation responses observed, and to thereafter exploit these mechanisms [8-10]. In their original article, Baughman et al. proposed that the high actuation performance of single wall nanotube (SWNT) sheets, upon charge injection and immersion in an aqueous electrolyte, was likely due to some combination of two phenomena: (1) the quantum-mechanical (QM) effect, and (2) the Coulomb effect [7]. QM actuation results from covalent C−C bond expansion/contraction upon the injection of excess electrons/holes, while the Coulomb effect arises from the electrostatic double-layer (EDL) that forms aside a charged surface to screen it. Notably, these two phenomena are rather different in
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