Delivered by Ingenta to: Rice University IP: 185.2.32.148 On: Wed, 15 Jun 2016 07:56:07 Copyright: American Scientific Publishers Copyright © 2007 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoscience and Nanotechnology Vol. 7, 2473–2479, 2007 Sonochemical Synthesis of Platinum Nanowires and Their Applications as Electro-Chemical Actuators Shaoxin Lu, Kousik Sivakumar, and Balaji Panchapakesan ∗ Department of Electrical Engineering, University of Delaware, Newark, Delaware 19716, USA We report the sonochemical synthesis of platinum nanowires on carbon nanotube templates and theirapplicationinelectrochemicalactuation.Thefabricationofplatinumnanowireswasachievedby suspending well separated single wall carbon nanotubes in isopropyl alcohol and ultra-sonically agi- tating the solution in the presence of dihydrogen hexachloroplatinate. The platinum nanowires were further processed into micro and macro scale free standing sheets by vacuum filtration. An electro- chemical cantilever actuator was constructed using the platinum nanowire sheet which actuated under electrical bias. Displacement of ∼3 mm was readily achieved when the electrical potential was swept at low voltages between −2 V and 2 V at a scan rate of 200 mV/s. The actuator showed the metallic actuation characteristics instead of that from carbon nanotubes. These results show the applicability of metallic nanomaterials for actuation technologies. Keywords: Carbon Nanotube, Platinum Nanowire, Sonochemical, Electro-Chemical Actuator. 1. INTRODUCTION Materials that have reversible dimensional changes upon application of external electrical stimulus are of great importance for actuation in many applications such as robotics, optical fiber switches, optical displays, micro pumps, and other types of actuator applications. Of these materials piezoelectric ceramics, shape memory alloys, magnetostrictive materials are well known. Conducting polymers and carbon nanotube actuators have been pro- posed to be attractive candidates for actuation for many applications. 1 However, the voltage induced dimension changes have only been recently reported for metals. 2 The strain achieved in the metallic actuators of ∼0.15% is better than piezoelectric materials. However, the time required for obtaining the maximum allowable strain or dimensional changes in these metallic nanoparticle mate- rials is quite large, of the order of several minutes. It was suggested that at “low” charge injection levels, quantum mechanical effects due to the charge injection lead to a strain in nanomaterials. The large surface area and the small dimensions of these nanomaterials that make the electrolyte-accessible area very large, together with the nanometer scale separation of charges at the interface between nanomaterials and electrolytes, lead to super capacitance in the actuator, which is the key factor for achieving high actuator strains at low voltages. 1 2 ∗ Author to whom correspondence should be addressed. Moreover, from the studies of Gleiter et al., it was sug- gested that nanometer-sized structures might open the way of modifying the electronic structure (such as charge car- rier density) and related properties of solids. 3 The depen- dence of surface stress of clean metal surfaces on the surface charge density has been predicted based on Jel- lium model although the amount of strain predicted by this model is comparatively small. 2 4 5 First principles calcula- tions of the charged Au(111) surface by density functional theory support the importance of the changes in the sur- face electronic structure to the surface stress and surface relaxation. 2 6 All these suggest that the surface charge modulation of nanomaterials could lead to mechanical actuation. The advantages of using metals for actuation are their stability at high temperatures and harsh environments. The higher strength of metals compared to polymeric materials makes them attractive against wear and promises stable operation over long periods of time. Hence there is signif- icant need for metallic actuators if one could make com- posite structures of high strength materials based on metals by arranging tiny nanoparticles of metals on templates to form a wire structure for sensing and actuation technolo- gies. While previous approaches of making nanowires have focused on fabricating nanowires with smooth surfaces, fabricating nanowires by arranging tiny nanoparticles into a wire structure has many advantages. The high surface area to volume ratio that is achieved in these nanowires J. Nanosci. Nanotechnol. 2007, Vol. 7, No. 7 1533-4880/2007/7/2473/007 doi:10.1166/jnn.2007.427 2473