The effects of alkaline earth metal salts on the performance of a polymer actuator based on single-walled carbon nanotube-ionic liquid gel

Abstract

The effects of alkaline earth metal salts (Magnesium bis(trifluoromethanesulfonyl)imide (Mg[TFSI] 2) and Calcium bis(trifluoromethanesulfonyl)imide (Ca[TFSI] 2)) on electrochemical and electromechanical properties of an actuator using a polymer-supported single-walled carbon nanotube (SWCNT)-ionic liquid (IL) gel electrode were investigated. The ionic conductivities of the gel electrolyte layers with the molar ratios of Mg[TFSI] 2/1-ethlyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI[TFSI]) = 0.05, 0.1 and 0.25, and Ca[TFSI] 2/EMI[TFSI] = 0.05, 0.1 and 0.25 were higher than that containing only EMI[TFSI]. We found large capacitance value 51–89 Fg −1 at a slow sweep rate 1 mV s −1. The generated strains of the polymer-supported SWCNT-IL gel electrodes of the actuators with the molar ratios of Mg[TFSI] 2/EMI[TFSI] = 0.1 (in all frequency range; 100–0.005 Hz) and Ca[TFSI] 2/EMI[TFSI] = 0.05 and 0.1 (in the frequency range; 1–0.005 Hz) were larger than that containing only EMI[TFSI]. In previous paper, the effects of Li salts (Li[BF 4] and Li[TFSI]) on the electrochemical and electromechanical properties of an actuator using a polymer-supported SWCNT-IL gel electrode were investigated. Consequently, the generated strain of the actuator with the molar ratios of Mg[TFSI] 2/EMI[TFSI] = 0.1 is larger than those containing Ca[TFSI] 2/EMI[TFSI], Li[TFSI]/EMI[TFSI] and Li[BF 4]/EMI[BF 4] for the wide frequencies (100–0.005 Hz). As the summary, the actuator containing Mg[TFSI] 2/EMI[TFSI] or Ca[TFSI] 2/EMI[TFSI] performed much better than that containing only IL. It is considered that the higher ionic conductivity of the gel electrolyte layers containing Mg[TFSI] 2/EMI[TFSI] or Ca[TFSI] 2/EMI[TFSI] produces the quick response actuators, and that the large capacitance gives large generated strain. The actuator containing Mg[TFSI] 2/EMI[TFSI] performed much better than those containing Ca[TFSI] 2/EMI[TFSI], Li[TFSI]/EMI[TFSI] and Li[BF 4]/EMI[BF 4] for the wide frequencies (100–0.005 Hz). These results are considered to be the actuator enough to apply actual applications (e.g. tactile display).