A Combined Experimental and Theoretical Approach to Understand the Structure and Properties of N‐Methylpyrrolidone‐Based Protic Ionic Liquids

Abstract

Correlation of the structure and properties of ionic liquids (ILs) is essential for the development of optimized materials in the fields of gas capture and separation, battery electrolytes, and cellulose dissolution processes. In view of this, a detailed vibrational spectroscopic analysis and quantum-chemical calculations were performed to explore the interionic interactions in ILs based on the N-methylpyrrolidone cation and a carboxylate anion. FTIR and Raman spectroscopy were applied to identify the hydrogen-bonding interactions between ion pairs, in which redshifted vibrational modes were observed as a function of the anion chain length. This observation was verified by the bond lengthening and enhanced hydrogen-bonding energies, as manifested in the structure and natural bond orbital (NBO) calculations. Furthermore, conductivity was measured at different temperatures to envisage the effect of the alkyl chain on the mobility of ions in the ILs. Finally, rheological measurements were implemented to explain the flow behavior of these ILs, which revealed a decrease in shear viscosity with an increase in temperature, that is, a Newtonian trend over a range of shear rates. The observed trend in transport properties was supported by the ion-pair binding energy. Stronger interactions between the IL cations and anions led to a decrease in the number of free ions and lowered the conductivity. In these protic ILs, the intermolecular N-H⋅⋅⋅O and C-H⋅⋅⋅O interactions played an important role in governing their physicochemical properties.

Molecular-Level Insights into the Microstructure of a Hydrated and Nanoconfined Deep Eutectic Solvent

“…This is very close to the idealized Newtonian fluid behavior, where the η values are found to be fully independent of γ . In the further analysis, the apparent viscosity (η a ) of the RM systems was calculated from the Herschel–Bulkley equation , where dγ / d t , n , τ, and τ a are the shear rate, H–B index, shear stress, and apparent yield stress, respectively. For the Newtonian-flow behavior, the n value can be considered as equal to 1 .…”

“…This is very close to the idealized Newtonian fluid behavior, where the η values are found to be fully independent of γ. 72 In the further analysis, the apparent viscosity (η a ) of the RM systems was calculated from the Herschel−Bulkley equation 73,74 i k j j j y…”

Effect of Ethylene, Diethylene, and Triethylene Glycols and Glycerol on the Physicochemical Properties and Phase Behavior of Benzyltrimethyl and Benzyltributylammonium Chloride Based Deep Eutectic Solvents at 283.15–343.15 K

“…Understanding the behavior of DESs in the presence of variable stress and shear rate is useful in analyzing their prospective applications in fields like CO 2 capture . From the obtained results, it can be concluded that DESs behave similar to liquid solvents as well as some IL samples …”

“…45 From the obtained results, it can be concluded that DESs behave similar to liquid solvents as well as some IL samples. 46 3.7. Ionic Conductivity.…”

Recent Research on Strategies to Improve Ion Conduction in Alkali Metal‐Ion Batteries

“…The Li ionic conductivity is found to increase due to the anisotropic negative thermal expansion along the hexagonal c‐axis. In addition, the problems focused on computational studies include: electronic structure calculation,, ion extraction number studied by discussing ion occupancy, ion interaction in ionic liquid (ILs), etc.…”