Ultraslow Dynamics at Crystallization of a Room-Temperature Ionic Liquid, 1-Butyl-3-methylimidazolium Bromide

Abstract

We studied the crystallization process of 1-butyl-3-methylimidazolium bromide ([C(4)mim]Br) using measurements of supersensitive scanning calorimetry, free induction decay (FID) signals of (1)H NMR, and direct observation. These three methods provided consistent, complementary results, which showed extremely slow dynamics at crystallization. This sample does not crystallize during the cooling process, loses mobility, and changes to a coagulated state, which is not the thermodynamic glass state. The FID signals and direct observation in the heating process indicate that the coagulated sample liquefies just before crystallization. The crystallization of [C(4)mim]Br does not occur from specialized locations such as the surface or wall of the sample tube but randomly in the liquid. The calorimetric measurements show that it takes 150 min for approximately 3 mg of this sample to crystallize perfectly. Conformational changes of the butyl group continue for approximately 330 min after crystallization. Such slow dynamics are thought to be due to the cooperative linking of crystallization and complex conformational changes in dense fields with high viscosity.

A review of NMR methods used in the study of the structure and dynamics of ionic liquids

“…Their relaxation studies confirm the rotation of some 13 C carbon atoms even in their crystalline state and/or solid state . The crystallization process of [BMIM][Br] has also been reported by the same research group from the calorimetric measurement that has been supported by the NMR T 1 and T 2 relaxation times . [BMIM][Br] appears to exist in three different states that are the coagulation, liquefaction, and the crystallization state that has been detected from the calorimetric measurements and are supported by their temperature dependent relaxation studies .…”

“…The crystallization process of [BMIM][Br] has also been reported by the same research group from the calorimetric measurement that has been supported by the NMR T 1 and T 2 relaxation times . [BMIM][Br] appears to exist in three different states that are the coagulation, liquefaction, and the crystallization state that has been detected from the calorimetric measurements and are supported by their temperature dependent relaxation studies . The temperature dependent dynamics of 1,3‐dimethylimidazolium bis(fluorosulfonyl)amide ([MMIM][FSA]) and 1,3‐dimethylimidazolium bis(trifluoromethylsulfonyl)amide ([MMIM][NTf 2 ]) has been investigated by using 19 F and 1 H NMR relaxation data .…”

Pressure and temperature effects on intermolecular vibrational dynamics of ionic liquids

“…Nevertheless, some detailed DSC investigations have been published showing that complex DSC scans of ionic liquids result from slow conformational dynamics. 36,38,39 The analysis of DSC measurements performed by Nishikawa et al 38,39 suggested that conformational changes of 1-alkyl-3-methylimizadolium cations take place as slow cooperative motions that affect local melting and/or crystallization, so that crystalline domains might remain even above the melting temperature.…”

Long Periodic Structure of a Room‐Temperature Ionic Liquid by High‐Pressure Small‐Angle X‐Ray Scattering and Wide‐Angle X‐Ray Scattering: 1‐Decyl‐3‐Methylimidazolium Chloride

“…Further, the appearance of T B suggests that the [C 10 mim][Cl] system possesses an intrinsic complexity. Furthermore, it is well known that the extremely slow dynamics of [C 4 mim][Br] are caused by the high viscosity . This indicates that the cooling rate governs the crystallization of high viscosity RTILs.…”