Influence of imidazolium-based ionic liquids on the performance of ionic polymer conductor network composite actuators

We investigated the influence of ionic liquids (ILs) on the electromechanical performance of ionic polymer conductor network composite (IPCNC) actuators. Four imidazolium ILs with two cations of different sizes, i.e. 1-ethyl-3-methylimidazolium ([EMI⁺]) and 1-butyl-3-methylimidazolium ([BMI⁺]), and two anions of different sizes, i.e. tetrafluoroborate ([BF₄^-]) and trifluoromethanesulfonate ([Tf^-]), were used. The IPCNC actuators were fabricated using a direct assembly method with RuO₂/Nafion^® nanocomposite as the electrode layers. The experimental results reveal that the actuator strain response time is nearly one order of magnitude shorter than the charging time. The IPCNCs with [EMI⁺][Tf^-] exhibit the highest capacitance and the fastest response in both actuation and electrical charging as capacitors. In contrast, the IPCNCs with [EMI⁺][BF₄^-] display the slowest charging time and lowest value of capacitance as capacitors. The IPCNCs with [BMI⁺][BF₄^-] showtheslowest response time. Furthermore, although the ILs used have a marked effect on the capacitances of the IPCNCs, using different ILs does not cause much change in themaximum strain of these IPCNCs. Consequently, the IPCNC actuatorswith [EMI⁺][BF₄^-] show the highest electromechanical conversion efficiency while those with [EMI⁺][Tf^-] have the lowest electromechanical efficiency because of the highest capacitance and largest input electrical energy. The experimental results indicate that the twooppositely charged ions contribute in opposite manner to the strain response and hence the observed shorter actuation response time is likely caused by the strain cancellation effect between the cations and anions.