title: Superpressing of a room temperature ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate.
abstract: We have investigated the phase behavior of 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF4]) at 298 K under high pressure conditions. We found that [emim][BF4] can be superpressed without crystallization up to ∼7 GPa. We propose that [emim][BF4] behaves as a superpressurized glass above 2.8 GPa. In view of the results, the environment around the alkyl-chain (C6 and C7-C8) of [emim][BF4] is largely perturbed rather than that around the imidazolium-ring in the superpressed state. We also discussed the results in view of the conformational isomerism of [emim](+) cation. Remarkably, as an alternative to pressure-induced crystallization, we have found that such a metastable liquid shows crystal polymorphism around 2.0 and 1.0 GPa upon decompression. The behavior is in contrast with the earlier results of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]).
authors.affiliation: Department of Applied Chemistry and ‡Department of Materials Science and Engineering, National Defense Academy , 1-10-20 Hashirimizu, Yokosuka, Kanagawa 239-8686, Japan.
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Yoshimura
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Abe
authors.forename: Takahiro
authors.initials: T
authors.lastname: Takekiyo
authors.forename: Machiko
authors.initials: M
authors.lastname: Shigemi
authors.forename: Nozomu
authors.initials: N
authors.lastname: Hamaya
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Wada
authors.forename: Minoru
authors.initials: M
authors.lastname: Kato
mesh_terms: D003460:Crystallization; D007093:Imidazoles / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*; D044367:Phase Transition; D011312:Pressure; D013059:Spectrum Analysis, Raman; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: C499119:1-ethyl-3-methylimidazolium tetrafluoroborate; D007093:Imidazoles; D052578:Ionic Liquids