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Ionic EAP actuators based on nano-carbon electrodes (Bucky-gel actuators)
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Update time: 2013-11-22
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Presented by Kinji Asaka, Leader of the Artificial Cell Research Group, Health Research Institute, National Institute of Advanced Industrial Science and Technology (AIST). 

Time: 10:00 a.m., Nov 27, 2013 

Location: A718, SINANO 

Abstract: 

Recently, it is well-known that carbon nanotubes (CNTs) are very attractive as electroactive polymer (EAP) actuator materials, since the CNTs provide extraordinary mechanical, electrical and electrochemical properties. Baughman et al. first reported that the single-walled CNT (SWNT) sheet show an electrochemical actuation when applying voltage against the counter electrode in aqueous electrolyte solution. On the other hand, in recent years, many organic materials have been synthesized as ionic liquids (ILs) or room temperature molten salts, which are known to be non-volatile, and show high ionic conductivities and wide potential windows. Therefore, we have developed a low-voltage driven dry actuator composed of ionic-liquid gel sandwiched of polymer-supported carbon-nanotube/ionic-liquid gel (bucky-gel) electrodes that is operable in air. The bending motion of the bucky-gel actuator is considered to be attributed to the dimensional changes of the electrode layers due to the ion transfers. The generated force/strain of the bucky-gel actuator is considered to be proportional to the electric charge in the electrode; that is proportional to the content of the dispersed SWNTs in the electrode layer. Hence, various dispersion techniques of SWNTs in the casting solution such as magnetic-stirring, ultrasonic dispersion, ball-milling, jet-milling, etc. have been developed. As a result, the performances of the bucky-gel actuators have much improved as compared to that of our first report. In addition, the various nano-carbons as electrode materials have been applied to improve the bucky-gel actuators successfully. The additives of various nano-carbons such as carbon blacks, poly-aniline coated carbon blacks. activated carbon nano-fibers, carbide-derived carbons, etc. with SWNTs in the electrode layers have been found to improve the generated strain and stress of the bucky-gel actuator. ILs are also critical components for determining the performance of the bucky-gel actuator . Seven kinds of ILs were studied, and EMIBFwas found to be the most optimized IL for the bucky-gel actuator. The mechanical and chemical properties of supported polymers also affect the actuator performance markedly. Several PVdF derivatives were tested for the supported polymers of the bucky-gel actuators. Optimum mixing of plastic and elastic PVdF materials resulted in the better bending performance. One disadvantage of the bucky-gel actuator is that the supporting polymer, essential for the actuator strip to possess a sufficient mechanical robustness, lowers the electrical conductivity, and the capacitance of the electrode layers. Therefore, we have developed a second-generation SWNT actuator composed of polymer-free nanotube electrodes, which shows a much better performance than previously reported ‘dry’ actuator, including the first generation design. This achievement was possible due to the finding that millimeter-long ‘super-growth’ carbon nanotubes (SG-SWNTs), produced by a water-assisted modified CVD method, associate together tightly with ionic liquids, affording a free-standing sheet with superb conductivity. The SG-SWNT actuator is capable to response at an applied sinusoidal voltage with a frequency of more than 100 Hz. We have studied frequency dependence of the generated strain and the electrochemical impedance spectroscopy of the bucky-gel actuator. We have developed a non-Faraday impedance modeling based on the porous electrode structure composed of the electron conductive film and ion conductive pore and successfully simulated the electromechanical frequency response of the bucky-gel actuators containing different kinds of ionic liquids. In this presentation, development of our bucky-gel actuators and some applications of them will be reviewed. 

Biography: 

KinjiAsaka received his phD degree in Science from Kyoto University in1990. He is currently a Group Leader of the Artificial Cell Research Group, Health Research Institute of National Institute of Advanced Industrial Science and Technology (AIST).  He is also currently an invited professor of Shinshu University and Wakayama University. His current research interests include interfacial electrochemistry and electroactivepolymer actuators.

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