Variable Thickness IPMC: Capacitance Effect on Energy Harvesting
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Variable Thickness IPMC: Capacitance Effect on Energy Harvesting Rashi Tiwari, Sang-Mun Kim and Kwang J. Kim Active Material Processing Laboratory, Mechanical Engineering Department, University of Nevada, Reno, NV 89511, U.S.A. ABSTRACT Ionic Polymer Metal Composites (IPMCs) are manufactured by electroless deposition of metal on Nafion. This deposition method results in the IPMCs with thickness between 0.17mm to 0.20mm with the electrode thickness of around a few µm each. It is now generally accepted that on mechanical deformation IPMC produces charge thus making these materials potentially suitable for energy harvesting applications. Due to thin metal plating and inherited flexibility of the Nafion film the IPMCs suffer in stiffness that may be required for some energy harvesting applications. Also earlier works have shown that 0.20mm thick IPMC produce better battery charging than 0.17mm thick one. Hot pressing, using metal mold, Nafion films was employed to produce thicker and comparatively stiffer IPMCs electroded with Palladium metal. Palladium was used because of shorter manufacturing time. This IPMC shows improved energy harvesting. Due to the increased thickness these IPMCs also function as better capacitors than their conventional counterparts. On application of voltage, these IPMCs show charging and discharging effects of a capacitor. This property of IPMC may be useful for storing charge. INTRODUCTION Power source for integrated electronics has been a growing concern with the ever-increasing use of portable devices. Recent advancements in the smart materials have led scientists to explore the application of these materials for energy harvesting applications. Ambient energy harvesting has many emerging applications in structural health monitoring, self-assembling devices, pacemakers, wireless devices and self-sustaining senor and actuators. IPMCs have previously not been given much attention for the same [1]. This provides a unique opportunity to characterize electromechanical property of IPMCs. Ionic polymers offer several advantages as energy harvester. Since the technology is comparatively new, there is potential for advancement as electromechanical transducers. Ionic polymers can sustain large strains making them ideal for the high stress environment [2]. High stress capabilities in turn allow the polymers to have a large stroke. Inherited flexibility, chemical stability and long life makes IPMC suitable for energy harvesting even in harsh environment [3]. Despite of these advantages, due to low output charge and time variant characteristics these are restricted in their application. The focus of this study is to increase the charge output from the IPMC. IPMC samples are typically manufactured from Nafion® 117 [4] as shown in Figure 1. The membrane is hydrated in D.I water for 24hrs and cleaned in water bath. Cleaned sample is then immersed in a metal salt solution for couple of hours. The reduction process using ammonia and sodium borohydride follows, which are put every half hour with te
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