Validation of Structural Grounds for Anomalous Molecular Mobility in Ionic Liquid Glasses

Abstract

Ionic liquid (IL) glasses have recently drawn much interest as unusual media with unique physicochemical properties. In particular, anomalous suppression of molecular mobility in imidazolium IL glasses vs. increasing temperature was evidenced by pulse Electron Paramagnetic Resonance (EPR) spectroscopy. Although such behavior has been proven to originate from dynamics of alkyl chains of IL cations, the role of electron spin relaxation induced by surrounding protons still remains unclear. In this work we synthesized two deuterated imidazolium-based ILs to reduce electron–nuclear couplings between radical probe and alkyl chains of IL, and investigated molecular mobility in these glasses. The obtained trends were found closely similar for deuterated and protonated analogs, thus excluding the relaxation-induced artifacts and reliably demonstrating structural grounds of the observed anomalies in heterogeneous IL glasses.

Glass-like behavior of intercalated organic solvents in graphite oxide detected by spin-probe EPR

“…4C) may be related to the glass-like cross-over in confined acetonitrile. Indeed, for bulk molecular glasses such as orthoterphenyl, 43 ethanol, 44 dibutyl phthalate, 45 or ionic liquids, 44,45 a correlation between the glass transition temperature T g and the enhancement of stochastic librations was observed. For confined solvents, the so-called dynamical cross-over is observed for various systems, including water in between GO planes.…”

Active Pharmaceutical Ingredient-Ionic Liquids (API-ILs): Nanostructure of the Glassy State Studied by Electron Paramagnetic Resonance Spectroscopy

“…In addition to characterizing the local rigidity/stiffness/fragility of ILs, the developed methodology also reveals so-called structural anomalies in ILs [29,30,[32][33][34]. In such anomalous temperatures regions near the glass transition, the molecular mobility decreases upon a temperature increase, which opposes general expectation for most media and materials [29,35].…”

Structural Anomaly in Glasses: Molecular Dynamics Study of Organic Radical in Dibutylphthalate at Different Temperatures

“…This is a highly uncommon behavior, since most known substances, including the same ILs in bulk, become less dense upon temperature increase, this was termed a “structural anomaly” [ 10 ]. Later on, it was demonstrated that such structural anomalies are governed by the alkyl chains of glass-forming compounds [ 11 , 12 , 13 ]. Furthermore, it was found that some non-IL compounds, such as those mimicking imidazolium cations, also exhibit similar structural anomalies.…”