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

Area of Science:

• Physical Chemistry
• Materials Science
• Condensed Matter Physics

Background:

• Ionic liquid (IL) glasses exhibit unique physicochemical properties and anomalous molecular mobility.
• Previous studies suggested temperature-dependent molecular mobility suppression in imidazolium IL glasses, observed via Electron Paramagnetic Resonance (EPR) spectroscopy.
• The influence of electron spin relaxation from surrounding protons on this anomalous behavior remained unclear.

Purpose of the Study:

• To investigate the role of proton-induced electron spin relaxation in the anomalous molecular mobility of imidazolium IL glasses.
• To differentiate between relaxation-induced artifacts and intrinsic structural effects governing IL glass dynamics.
• To synthesize and study deuterated imidazolium-based ILs to minimize electron-nuclear couplings.

Main Methods:

• Synthesis of deuterated imidazolium-based ionic liquids.
• Utilizing pulse Electron Paramagnetic Resonance (EPR) spectroscopy to probe molecular mobility.
• Comparative analysis of molecular mobility in both deuterated and protonated IL glasses.

Main Results:

• Molecular mobility trends in deuterated IL glasses were found to be closely similar to their protonated counterparts.
• The observed anomalous suppression of molecular mobility persisted in deuterated ILs, independent of proton presence.
• This similarity excludes relaxation-induced artifacts as the primary cause of the anomalous behavior.

Conclusions:

• The anomalous suppression of molecular mobility in imidazolium IL glasses is primarily due to structural factors within the heterogeneous glass network.
• Electron spin relaxation induced by surrounding protons does not significantly contribute to the observed anomalous mobility suppression.
• The findings provide reliable evidence for the structural origins of anomalous dynamics in ionic liquid glasses.