TY - JOUR

T1 - Dynamical heterogeneities in ionic liquids as revealed from deuteron NMR

AU - Khudozhitkov, Alexander E.

AU - Stange, Peter

AU - Bonsa, Anne Marie

AU - Overbeck, Viviane

AU - Appelhagen, Andreas

AU - Stepanov, Alexander G.

AU - Kolokolov, Daniil I.

AU - Paschek, Dietmar

AU - Ludwig, Ralf

N1 - Publisher Copyright: © 2018 The Royal Society of Chemistry.

PY - 2018/3/28

Y1 - 2018/3/28

N2 - The heterogeneity in dynamics has important consequences for understanding the viscosity, diffusion, ionic mobility, and the rates of chemical reactions in technology relevant systems such as polymers, metallic glasses, aqueous solutions, and inorganic materials. Herein, we study the spatial and dynamic heterogeneities in ionic liquids by means of solid state NMR spectroscopy. In the 2H spectra of the protic ionic liquid [TEA][OTf] we observe anisotropic and isotropic signals at the same time. The spectra measured below the melting temperature at 306 K could be simulated by a superposition of the solid and liquid line shapes, which provided the transition enthalpies between the rigid and mobile fractions. Consequently, we measured the spin-lattice relaxation times T1 for the anisotropic and the isotropic signals for the temperature range between 203 and 436 K. Both dispersion curves could be fitted to models including rotational correlation times, activation barriers and rate constants. This approach allowed determining the rotational correlation times for the N-D molecular vector of the [TEA]+ cation in differently mobile environments. The mobility is only slightly different, as indicated by small differences in activation energies for these processes. The NMR correlation times for the highly mobile phase are linearly related to measured viscosities, which supports the applicability of the Stokes-Einstein-Debye relation.

AB - The heterogeneity in dynamics has important consequences for understanding the viscosity, diffusion, ionic mobility, and the rates of chemical reactions in technology relevant systems such as polymers, metallic glasses, aqueous solutions, and inorganic materials. Herein, we study the spatial and dynamic heterogeneities in ionic liquids by means of solid state NMR spectroscopy. In the 2H spectra of the protic ionic liquid [TEA][OTf] we observe anisotropic and isotropic signals at the same time. The spectra measured below the melting temperature at 306 K could be simulated by a superposition of the solid and liquid line shapes, which provided the transition enthalpies between the rigid and mobile fractions. Consequently, we measured the spin-lattice relaxation times T1 for the anisotropic and the isotropic signals for the temperature range between 203 and 436 K. Both dispersion curves could be fitted to models including rotational correlation times, activation barriers and rate constants. This approach allowed determining the rotational correlation times for the N-D molecular vector of the [TEA]+ cation in differently mobile environments. The mobility is only slightly different, as indicated by small differences in activation energies for these processes. The NMR correlation times for the highly mobile phase are linearly related to measured viscosities, which supports the applicability of the Stokes-Einstein-Debye relation.

KW - QUADRUPOLE COUPLING-CONSTANTS

KW - INTERACTION ENERGIES

KW - DISPERSION FORCES

KW - HYDROGEN-BONDS

KW - RELAXATION

KW - SOLVENTS

KW - MACROMOLECULES

KW - MIXTURES

KW - FUTURE

KW - MEDIA

UR - http://www.scopus.com/inward/record.url?scp=85044285515&partnerID=8YFLogxK

U2 - 10.1039/c7cc09440j

DO - 10.1039/c7cc09440j

M3 - Article

C2 - 29464242

AN - SCOPUS:85044285515

VL - 54

SP - 3098

EP - 3101

JO - Chemical Communications

JF - Chemical Communications

SN - 1359-7345

IS - 25

ER -