Abstract
This study presents the results of the pressure-induced Raman spectral changes in two ionic liquids (ILs): 1-propyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide and 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, up to ∼8 GPa. The results with those of the samples comprising an unmethylated C2-H group in the imidazolium cations, that is, 1-propyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide were compared. Along with the visual observations, none of the samples showed crystallization; conversely, the methylated samples exhibited a pressure-induced glass transition with a significant structural organization around 2 GPa, where the glass transition pressures were higher than those of their unmethylated counterparts. This unexpected glass transition behavior in terms of the results from the local structural changes of cations and anions with the aid of molecular dynamics calculations are discussed. Present study highlights that the methylation of the C2-H group in the cation is an alternative way to adjust the interactions within ILs, which expands the potential of ILs for applications under high-pressure conditions.
Published Version
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