Dynamics of Pyrrolidinium-Based Ionic Liquids under Confinement. II. The Effects of Pore Size, Inner Surface, and Cationic Alkyl Chain Length

In recent years, ionic liquids (ILs) have been developed as novel solvents, electrolytes, and functional materials for numerous applications in diverse fields. Of interest is confining ILs into various nanoporous matrices, which not only solves the drawbacks of ILs due to their fluid nature, for example, electrolyte leakage in batteries, but also endows these systems with distinctly different physicochemical properties relative to the bulk counterparts. In-depth studies on the effect of nanoscale confinement as well as the interactions between ILs and the pore walls should facilitate the development of task-specific IL nanomaterials. Here, using broadband dielectric spectroscopy and differential scanning calorimetry, we have investigated the dynamics and electrical conductivity of pyrrolidinium-based ILs with the bis(trifluoromethanesulfonyl)imide anion ([Tf₂N]^-), infiltrated into nanoporous anodized aluminum oxide membranes. The effect of pore size, inner surface modification (silanization), and cationic alkyl chain length on properties of confined ILs was examined in detail. For some thermodynamic conditions, we observed much faster dynamics and higher conductivity for the confined IL compared to the bulk case. Thus, our results provide a better understanding of how to tune the conductivity behavior of the ionic system and how to design novel electrochemical nanodevices with tailored-based properties.