Vol.9 No.3 2017

Research paper : Development of human-friendly polymeric actuators based on nano-carbon electrodes (Kinji Asaka)−119−Synthesiology - English edition Vol.9 No.3 (2017) soaked them with ionic liquids, and fabricated the actuator element. Yet, we could not obtain good results. During this time, we were introduced to bucky gel research by Researcher Takanori Fukushima (currently, Professor, Tokyo Institute of Technology) of the JST ERATO Aida Project in 2003, and we commenced joint research for its application to actuators. Fukushima et al. discovered the phenomenon in which a gel was formed when CNTs and ionic liquids are ground together in a mortar, and this gel was named bucky gel.[8] Fukushima et al. also found that this phenomenon occurred as the imidazolium cation of the ionic liquids bonds with the π electron of CNTs, bridges the CNTs, and forms the gel.[8] We started the joint research for using the gel as the actuator electrode.While the CNTs have various excellent properties as actuator electrodes as mentioned earlier, the problem was how to form them into an electrode. In forming the electrode from the CNT materials, the electrode must be made by dispersing the individual molecules of CNTs so they may come into contact with the electrolytes, or the characteristic large specific surface area cannot be utilized, and the electrode will not store the ions. We thought the reason we failed with the paper electrode described earlier was because of this point.The technology of the CNT bucky gel using ionic liquids was considered ideal as a manufacturing method of actuator electrodes because it solved the problem of CNT dispersal, and the ionic liquids themselves would become the electrolytes. Moreover, this electrode forming method would be applicable to a low-cost mass production method such as printing and casting. However, A bucky gel of CNTs and ionic liquids only was too soft as an actuator electrode. Therefore, poly(vinylidene fluoride-co-hexafluoropropene) [PVdF (HFP)] that has good compatibility with ionic liquids was added as a mechanical support polymer to form the electrode. Using the ion gel of PVdF (HFP) and ionic liquids as the ion conductive polymer, we succeeded in developing the actuator element with three layers as shown in Fig. 3.[9][10] As described in the initial scenario, this element is a low-voltage-driven soft actuator with the following characteristics: 1) uses materials whose costs can be reduced; 2) can be fabricated by a simple process; 3) uses electrode materials with large capacitance; and 4) uses ion conductive polymers that can be operated in air.5 Characteristics of the bucky gel actuator and the scenario for its applicationThe characteristics of the developed bucky gel actuator will be summarized. The manufacture method is extremely simple. The solution, in which the components of the CNT electrode layer and the ion gel layer are well dispersed, is prepared, the solvent is evaporated by casting, electrode lms and an ion gel lm are manufactured, and the ion gel lm is sandwiched with the electrode lms and hot pressed together. It is possible to apply this to mass production methods such as printing.The principle of deformation response is as shown in Fig. 4, and the deformation occurs as the ions move to the respective electrodes upon application of voltage, and the electrode layers expand or contract. A thin actuator film with large deformation at voltage of 3 V or less can be obtained, as shown in Fig. 5. The characteristics of the bucky gel actuator are as follows: 2) it is a thin lm, 3) has large deformation, 3) is low-voltage driven, and 4) has good workability. Utilizing these characteristics, developments of basic materials through joint research with the JST Aida Project, and by AIST alone Fig. 3 Schematic diagram of the structure of the bucky gel actuatorPolymerCarbon nanotubeIonic liquidNNRH3CBF4-CF3CFCF2CF2CH20.120.88nNanocarbonIonic liquidPolymerElectrode layer (Nanocarbons/ionic liquids/polymers)Ionic gel layer (ionic liquids/polymers)Fig. 4 Deformation response principle of the bucky gel actuator

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