POSS fillers for modulating the thermal properties of ionic liquids

Abstract

We report a polyhedral oligomeric silsesquioxane (POSS)-based filler for improving the thermal properties of ionic liquids (ILs). We prepared homogeneous mixtures containing the octa-substituted carboxy-POSS as a filler via a solution process. Initially, it was found that the melting temperatures of the ionic pairs were lowered by adding the POSS filler. Based on this effect, some of ionic salts were transformed into ILs by adding the POSS filler. Reinforcement of thermal stability was also observed from the salts which have an intrinsically low decomposition temperature. According to the thermodynamic parameters in melting, the introduction of the POSS filler significantly reduces both the fusion enthalpy and entropy. Furthermore, from experiments on the substituent effect on POSS, it was found that only octa-carboxy POSS had an effect on the modulation of the thermal properties of ion salts. Considering these results, we summarized that the highly symmetrical rigid structure of the silica cage could be responsible for the improvement of the thermal properties of the ion salt matrices via the strong interaction between the carboxyl groups and the ion salt matrices. Our concept is feasible not only for the conversion of conventional ionic salts into ILs, but also for the development of new series of ILs.