Ionic Liquid-Tethered Nanoparticle Suspensions: A Novel Class of Ionogels

We report a novel class of silica ionogels created by dispersing silica nanoparticles densely grafted with the ionic liquid (IL) 1-trimethoxysilyl propyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl) imide (SpmImTSFI) in a 1-butyl-3-methyl-pyrrolidinium bis(trifluoromethylsulfonyl) imide (BmpyrTFSI) IL host. We find that over the entire range of nanoparticle volume fractions studied the systems exist as stable suspensions of SiO2-SpmImTFSI in the BmpyrTFSI host. Remarkably, we also find that addition of even minute quantities of SiO2-SpmImTFSI to the BmpyrTFSI IL suppresses crystallization of the host. The resulting disordered hybrid fluids exhibit liquid-like transport properties over a vastly extended temperature range; they open the way for facile synthesis of ILs with extended operating temperature windows. These observations are explained in terms of ionic coupling of the nanoparticle-tethered and free TFSI anions, which is thought to suppress crystallization of BmpyrTFSI.