Electromechanical Behavior of Fully Plastic Actuators Based on Bucky Gel Containing Various Internal Ionic Liquids

In the previous papers, we have reported the first dry actuator that can be fabricated simply by layer-by-layer casting, using ‘bucky gel’, a gelatinous room-temperature ionic liquid (IL) containing single-walled carbon nanotubes (SWNTs). In this paper, the electromechanical and electrochemical properties of the bucky-gel actuators composed of the bucky-gel electrode and the gel electrolyte layers containing seven kinds of internal ILs were studied for exploring the details of the actuation mechanism. We measured the frequency dependence of the displacement response of the bucky-gel actuator and it can be successfully simulated by the electrochemical kinetic model. From the simulated result for the frequency dependence of the electromechanical response of the bucky-gel actuators, we determined two parameters for the simulation, the generated strain at a limit of low frequency and the time constant. The time constant was represented by the equivalent circuit composed of series combination of the ionic resistance R, the double-layer capacitance C and the electrode resistance Rel. The IL-dependence of the time constant was determined by that of the ionic resistance R of the gel electrolyte layer. The generated strain at a limit of low frequency is considered to be related to the electromechanical mechanism of the bucky-gel actuator. From their dependence on the IL species and the theoretical modeling reported in the previous papers, we conclude that both the steric repulsion effect due to the transfer of ions to the electrode and ‘the charge injection’ give the bending motion of the bucky-gel actuator. The volume-changes of the cathode and anode change according to the sizes of the cation and anion, respectively. The ion size gives the dependence of the bending motion of the bucky-gel actuator on the internal ionic species.