title: Phase behaviors of room temperature ionic liquid linked with cation conformational changes: 1-butyl-3-methylimidazolium hexafluorophosphate.
abstract: We have investigated phase-transition behaviors of a typical room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([C(4)mim]PF(6)), using calorimetric and Raman spectroscopic techniques. Although there was some confusion on its phase behaviors in previous reports, our measurements with a laboratory-made calorimeter at a slow scanning rate (5 mK/s) have definitely revealed that [C(4)mim]PF(6) has three crystalline phases. From the Raman spectroscopic study, the conformations of the butyl group for these crystalline phases are assigned to gauche-trans, trans-trans, and gauche'-trans conformations in lower-energy order. It has been also shown that these three conformers coexist in the liquid, supercooled liquid, and glass states. It is concluded that all of the phase transitions of [C(4)mim]PF(6) except the glass transition are associated with conformational changes of the butyl group.
authors: Graduate School of Advanced Integration Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan.
authors: Takatsugu
authors: T
authors: Endo
authors: Tatsuya
authors: T
authors: Kato
authors: Ken-ichi
authors: K
authors: Tozaki
authors: Keiko
authors: K
authors: Nishikawa