Vol.9 No.3 2017

Research paper : Development of human-friendly polymeric actuators based on nano-carbon electrodes (Kinji Asaka)−120−Synthesiology - English edition Vol.9 No.3 (2017) were conducted. Then, from 2006–2007, the development to achieve a high performance actuator for human-friendly devices was conducted through joint development with a private company.The human-friendly devices in which the polymeric actuators are needed include the devices worn on the body that require polymeric actuators that are soft, light, and low-voltage driven. The size of the devices can be divided into large human-sized devices such as Power Assist, and thin and light devices such as wearable micro-pumps and portable information display devices. The former was positioned as a future issue that necessitates upsizing technology through polymeric actuator stacking. For the latter, development of materials was continued to realize the application of polymeric actuators to thin and light devices by improving the bending strength, responsiveness, and bending displacement of the actuators.6 Improvement of the performance of bucky gel actuatorsHere, the points in improving the performance of bucky gel actuators are summarized from the perspective of materials development. Since the driving principle of this actuator is the polarization of ions to electrodes, the keys are the development of a material that increases polarization to improve the generative force and displacement, and the development of a material that increases the polarization speed to improve the response rate. Based on this basic way of thinking, the following materials development was started in 2007 jointly with corporations, toward application to thin and light human-friendly devices. Refer to Reference [11] for details of the materials development.6.1 Improvement of nanocarbon dispersibilityAs mentioned earlier, the dispersal of nanocarbons in the electrode layer is closely related to the conductivity, capacitance, and Young’s modulus of the electrode layer. By increasing the nanocarbon content with good dispersibility, it is possible to manufacture electrodes with high conductivity and capacitance, and the actuator performance is expected to increase.The single-layered CNTs have excellent performance but have poor dispersibility, and it was conventionally considered difcult to bring out the individual performance when forming them into electrodes or other products. We used the ionic liquids as dispersants, used various dispersing methods such as ultrasound, ball mill, or jet mill, developed the process for dispersing the single-layered CNTs and manufactured the electrode in which the CNTs were dispersed in high concentration. Also, we found that the actuator performance increased dramatically by adding carbon black (CB) and carbon nanohorn (CNH) to the CNT electrode layer. Therefore, we succeeded in manufacturing an excellent actuator electrode by seeking the optimal dispersing condition of such mixed electrodes.From the above, it can be inferred that the properties required for electrode nanocarbons are not simply mechanical properties of single elements such as conductivity, initiation stress, expansion/contraction ratio, specic surface area, or Young’s modulus, but also involve geometric factors such as aforementioned dispersibility or aspect ratio that appear as the properties of an assembly of elements. The improvements of actuator performance by the addition of CB and CNH are thought to be achieved through the contribution not only of the conductivity and capacitance of CB or CNH, but the contribution of their geometric factors such as enhanced dispersability of CNTs or increased density of the electrode structure.We have sought the optimal electrode composition and its dispersal conditions through experience, but in the future, we wish to engage in research for quantitative evaluation of the dispersability in relation to actuator performance, to develop a nanocarbon polymeric actuator with higher performance.6.2 Ionic liquidsThe factor that determines the performance of this actuator along with the nanocarbon electrode is the ionic liquids used. Based on the deformation model shown in Fig. 4, we looked at the size difference of the cation and anion in terms of displacement, and looked at the ion conductivity for the displacement rate. Using five types of imidazole ionic liquids and two types of quaternary ammonium ionic liquids that were used frequently in electrochemical devices, we manufactured the actuator lms, compared their performances, and sought the optimal ionic liquids. As a result, we obtained guidelines for the selection of the ionic liquids based on the deformation model of Fig. 4 as follows: 1) the rate of response of the actuator is determined by the ion conductivity and electrode conductivity, and 2) the degree of displacement response is dependent on the size difference of the cation and anion.3 VFig. 5 Deformation of the bucky gel actuator at 3 V applied voltage

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