Fabrication of Ionic Polymer Metal Composite Actuator with Palladium Electrodes and Evaluation of its Bending Response

We built up the way of fabricating IPMC actuator with palladium electrodes and we found that it showed large bending response than Au-plated IPMC actuator. An ionic polymer-metal composite (IPMC) consisting of a thin perfuorinated ionomer membrane, electrodes plated on both faces, undergoes large bending motion when a small electric field is applied across its thickness in a hydrated state. The characteristics of IPMC are ease of miniaturization, low density, and mechanical flexibility. Therefore, it is considered to have a wide range of applications from MEMS sensor to artificial muscle. However, there are problems on IPMC. First, its mechanical and electric characteristics have not been clarified because of the complex mechanism of the deformation. Second, it is high-priced because most of IPMC actuators use gold or platinum as electrodes. In order for IPMC actuator to be widely put to practical use, we should solve these problems. Hence, this research focuses on fabrication of IPMC actuator with palladium electrode, which is cheaper than gold or platinum, and evaluation of its mechanical properties such as its tip displacement. We fabricated IPMC consisting of a thin Nafion® membrane, which is the film with fluorocarbon back-bones and mobile cations, sandwiched between two thin palladium plates. The surface resistivity was 2.88±0.18Ω/sq., so it could be said to be enough small. Then, we observed its cross section by using FE-SEM. As a result, palladium plates were evenly coated and its thickness was about 30μm. Also, we carried out an actuation test for two kinds of IPMCs: one was fabricated by using Nafion®117 (thickness 183μm), the other was by Nafion®115 (thickness 127μm). In this test, the relationship between voltage (0˜4V) across its thickness and tip displacement for the cantilevered strip of the IPMC was measured. Then we found that IPMCs showed large bending motion under a low electric field. When Nafion®117 sample was subjected to voltage of 1.5V, the ratio of the tip displacement to the sample length was 0.35, which was lager bending than Au-plated IPMC actuator, whose ratio of the tip displacement to the sample length was 0.12 [1]. When Nafion®115 sample was applied to 1.5V, the ratio of the tip displacement to the sample length was 0.22. Then, we found that Nafion®117 bended in a larger way than Nafion®115. Reference [1]Sia Nemat-Nesser and Yongxian Wu,”Comparative experimental study of ionic polymer-metal composites with different backbone ionomers and in various cation forms”, Journal of Applied Physics,93,5255 (2003)