Rotational and translational dynamics and their relation to hydrogen bond lifetimes in an ionic liquid by means of NMR relaxation time experiments and molecular dynamics simulation

Abstract

We report a concerted theoretical and experimental effort to determine the reorientational dynamics as well as hydrogen bond lifetimes for the doubly ionic hydrogen bond +OH⋯O− in the ionic liquid (2-hydroxyethyl)trimethylammonium bis(trifluoromethylsulfonyl)imide [Ch][NTf2] by using a combination of NMR relaxation time experiments, density functional theory (DFT) calculations, and molecular dynamics (MD) simulations. Due to fast proton exchange, the determination of rotational correlation times is challenging. For molecular liquids, 17O-enhanced proton relaxation time experiments have been used to determine the rotational correlation times for the OH vectors in water or alcohols. As an alternative to those expensive isotopic substitution experiments, we employed a recently introduced approach which is providing access to the rotational dynamics from a single NMR deuteron quadrupolar relaxation time experiment. Here, the deuteron quadrupole coupling constants (DQCCs) are obtained from a relation between the DQCC and the δ1H proton chemical shifts determined from a set of DFT calculated clusters in combination with experimentally determined proton chemical shifts. The NMR-obtained rotational correlation times were compared to those obtained from MD simulations and then related to viscosities for testing the applicability of popular hydrodynamic models. In addition, hydrogen bond lifetimes were derived, using hydrogen bond population correlation functions computed from MD simulations. Here, two different time domains were observed: The short-time contributions to the hydrogen lifetimes and the reorientational correlation times have roughly the same size and are located in the picosecond range, whereas the long-time contributions decay with relaxation times in the nanosecond regime and are related to rather slow diffusion processes. The computed average hydrogen bond lifetime is dominated by the long-time process, highlighting the importance and longevity of hydrogen-bonded ion pairs in these ionic liquids.

Ion Transport and Electrochemical Properties of Fluorine-Free Lithium-Ion Battery Electrolytes Derived from Biomass

“…The diffusion coefficients of ions for the different Li salt concentrations are different as can be seen in Figures and S8–S10. In a series of previously published reports, − diffusion of a number of ILs was studied together with some other macroscopic transport properties such as viscosity and ionic conductivity. In these studies, a unique diffusion coefficient for each ion has been obtained.…”

“…For complex liquids with larger molecules, such as glycerol and n -propanol, the neutron experiments have indicated that the true molecular diffusive motion is a mixed translational–rotational–vibrational displacement . For (2-hydroxyethyl)­trimethylammonium bis­(trifluoromethylsulfonyl)­imide IL, the simulated correlation function comprises two independent domains: the short-time performance declines within the picosecond time interval determine re-orientational correlation times, while the long-range nanosecond interval is actually accredited to the translational diffusion.…”

Polarization of ionic liquid and polymer and its implications for polymerized ionic liquids: An overview towards a new theory and simulation

“…Thus, ILs can be both high and low dielectric media, and therefore, the dielectric responses of the cations and anions in ILs may be critical to understanding the thermodynamic and electrochemical properties of IL-based materials. 60 Moreover, specific interactions such as hydrogen bonding and aromatic interaction often exist in ILs and are of particular importance in the physical properties of ILs, [77][78][79][80][81][82][83][84][85][86][87] thus allowing us to distinguish ILs from inorganic salts. Indeed, Dupont proposed that 1,3-dialkylimidazolium ILs are described as hydrogenbonded polymeric supramolecules.…”

“…Moreover, specific interactions such as hydrogen bonding and aromatic interaction often exist in ILs and are of particular importance in the physical properties of ILs, 77–87 thus allowing us to distinguish ILs from inorganic salts. Indeed, Dupont proposed that 1,3‐dialkylimidazolium ILs are described as hydrogen‐bonded polymeric supramolecules 31 .…”

Analisis Molekular dan Transpor Ion Natrium Silikat

“…Nilai konduktivitas panas yang dihasilkan berkisar antara 1,89 W/mK -3,61 W/mK (79; 165; 166; 174) Perhitungan Konduktivitas: Diketahui untuk persen massa 1,5% dan konduktifitas listrik 4,0, maka konduktivitas molar dapat ditentukan dengan persamaan : Bilangan transport merupakan fraksi dari arus total yang dibawa oleh ion jenis tertentu.untuk larutan dengan 2 jenis ion (178)(179)(180)(181), bilangan dengan I + merupakan arus kation, I adalah arus total yang melalui larutan, dan Iadalah arus anion. Dapat diasumsikan sebagai: I + + I -= I (179)(180)(181)(182)(183) Bilangan transport merupakan pembatas t o , namun untuk limit konsentrasi nol dari larutan elektrolit itu (184)(185)(186)(187)(188) . Arus yang berasal dari setiap jenis ion berhubungan dengan mobilitas ion.…”