RESUMEN

Crystal polymorphs of fluorinated ionic liquids (fILs) were examined at low-temperature (LT) by Raman spectroscopy. The fILs were 1-alkyl-3-methylimidazolium perfluorobutanesulfonate, [Cnmim][PFBS] (n = 4, 6, and 8). The cations and anion possess conformational degrees of freedom. Various LT phases were derived from the conformational polymorphs of the cations and the anion. Conformational flexibility depended on alkyl chain length. The crystal polymorphs in the fILs were sensitive to molecular conformations and flexibility.

Asunto(s)

Líquidos Iónicos , Líquidos Iónicos/química , Imidazoles/química , Conformación Molecular , Cationes/química , Aniones

RESUMEN

The Bragg reflections of 1-decyl-3-methylimidazolium chloride ([C10 mim][Cl]), a room-temperature ionic liquid, are observed in a lowly scattered wavevector (q) region using high-pressure (HP) small-angle X-ray scattering methods. The HP crystal of [C10 mim][Cl] was characterized by an extremely long periodic structure. The peak position at the lowest q (1.4 nm-1 ) was different from that of the prepeak observed in the liquid state (2.3 nm-1 ). Simultaneously, Bragg reflections at high-q were detected using HP wide-angle X-ray scattering. The longest lattice constant was estimated to be 4.3 nm using structural analysis. The crystal structure of HP differed from that of the low-temperature (LT) crystal and the LT liquid crystal. With increasing pressure, Bragg reflections in the high-q component became much broader, and were accompanied by phase transition, although those in the low-q component were observed to be relatively sharp.

RESUMEN

Using simultaneous small-angle X-ray scattering (SAXS) combined with differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS) combined with DSC measurements, low-temperature (LT) solid phases of a room-temperature ionic liquid (RTIL) and its mixtures were examined at ambient pressure. The considered RTIL was 1-methyl-3-propylimidazolium iodide ([C3mim][I]), and the mixtures could be expressed as [C3mim][Im]. Under high-pressure (HP), the crystallization of pure [C3mim][I] was suppressed, as a LT-amorphous form of pure [C3mim][I] was formed. In the mixed system, the HP crystallization of [C3mim][I3] occurred at 0.95 GPa of compression. In [C3mim][I3.66] as a non-stoichiometric system, complicated phase changes were observed. Upon compression, the edge of a sample container was crystallized. By further compression, a crystal-crystal phase transition was observed as a HP-crystal polymorph appeared. In the centre, HP amorphization was observed upon compression, whereas decompression crystallization was induced by decreasing the pressure. The HP complicated behaviors of non-stoichiometric [C3mim][I3.66] are caused by the excess of iodide/iodine.