Phase Behavior of a Piperidinium-Based Room-Temperature Ionic Liquid Exhibiting Scanning Rate Dependence

Abstract

The structural flexibility and conformational variety of the ions in room-temperature ionic liquids (RTILs) have significant effects on their physicochemical properties. To begin a systematic study of the thermodynamic properties of nonaromatic RTILs, 1-methyl-1-butylpiperidinium bis(fluorosulfonyl)amide ([Pip1,4][FSA]) was selected as the first sample. In addition to the rotational flexibility of the alkyl group, the [Pip1,4](+) cation has characteristic ring-flipping flexibility, which is very different from the behavior of the well-studied imidazolium-based cations. Calorimetry investigations using laboratory-made high-sensitivity calorimeters and Raman spectroscopy revealed that [Pip1,4][FSA] has two crystalline phases, Cryst-α and Cryst-β, and that every phase change is linked to conformational changes of both the cation and anion. Each phase change is also governed by very slow dynamics. The phase changes from supercooled liquid to Cryst-α and from Cryst-α to Cryst-β, which were observed only during heating, are not in fact phase transitions but structural relaxations. Notably, the temperatures of these structural relaxations exhibited heating rate dependences, from which the activation energy of the ring-flipping was estimated to be 38.8 kJ/mol. It is thought that this phenomenon is due to the associated conformational changes of the constituent ions in viscous surroundings.

Electrochemical and Physical Properties of Imidazolium Chloride Ionic Liquids with Pyrrolidinium or Piperidinium Cation Addition and Their Application in Dual‐Ion Batteries

“…In Figure 2b, two peaks of PP 14 + can be observed at 283 and 714 cm −1. [ 20 ] In general, the peak intensity of the cations was too weak to discern the change in the Raman spectrum and various mole ratios in this study, but the intensity of the AlCl 4 − anions remained stable, as expected. Vibrational assignments of anionic and cationic species in those IL electrolytes are shown in Table S1, Supporting Information.…”

Thermophysical Properties of Binary Amide Anion-Based Ionic Liquids; TMPAFSA<i>_x</i>TFSA₁₋<i>_x</i>

“…Such melting behavior is particularly common in materials which exhibit polymorphism, and it has been recently reported that ionic liquid exhibits polymorphic behavior. [32][33][34][35][36][37][38][39] Also in this work, there are several solid phases which have different segmental motion due to polymorphism, such solid phase exhibited melting behavior below the temperature corresponding to the solidus line. Additionally, we got composition dependence of heat of fusion as Fig.…”

Epoxy-Containing Ionic Liquids with Tunable Functionality

“…The differential scanning calorimetry (DSC) curves of the organic salts 1 – 4 are shown in Figure 2. Only 4 showed different phase transition behavior, i.e., very small exothermic peaks for the crystallization at ~279 K and the crystalline phase transition at ~299 K. Because it is not uncommon for ILs to show similar behavior, these phase changes could be governed by the very slow dynamics in 4 [27,28]. In addition to this behavior, a clear endothermic peak for the melting process at 363 K appeared in the DSC curve during the heating process.…”