Anion effects in imidazolium ionic liquids on the performance of IPMCs

Four ionic liquids were explored for as inner solvents of IPMC to overcome the shortcomings of water, especially its high volatility and low electrolysis potential. The imidazolium salts were composed of 1-ethyl-3-methylimidazolium [EMIm] cation and anions including bromide [Br], nitrate [NO3], acetate [AcO], and trifluoroacetate [TA]. The 1H NMR studies confirmed the structures of the four ionic liquids and indicated that [EMIm][AcO] and [EMIm][TA] had stronger interactions between anion and C(2) hydrogen in imidazolium cation compared with [EMIm][NO3] and [EMIm][Br]. [EMIm][Br] and [EMIm][NO3] exhibited enormously low volatility with initial weight loss above ca. 290 °C. Two-probe linear sweep voltammetry (LSV) revealed that the electrolytic stability decreased in the order of [EMIm][TA] > [EMIm][AcO] > [EMIm][NO3] ∼ [EMIm][Br], whereas current density in IPMCs was in the reverse order. Thus, [EMIm][Br]- and [EMIm][NO3]-based IPMCs exhibited a superior performance in terms of tip displacement and response speed compared to [EMIm][AcO]- and [EMIm][TA]-based ones. These results corresponded with the size and ionic mobility of anions in imidazolium salts.