Abstract
1H and 19F spin-lattice relaxation experiments have been performed for butyltriethylammonium bis(trifluoromethanesulfonyl)imide in the temperature range from 258 to 298 K and the frequency range from 10 kHz to 10 MHz. The results have thoroughly been analysed in terms of a relaxation model taking into account relaxation pathways associated with 1H–1H, 19F–19F and 1H–19F dipole–dipole interactions, rendering relative translational diffusion coefficients for the pairs of ions: cation–cation, anion–anion and cation–anion, as well as the rotational correlation time of the cation. The relevance of the 1H–19F relaxation contribution to the 1H and 19F relaxation has been demonstrated. A comparison of the diffusion coefficients has revealed correlation effects in the relative cation–anion translational movement. It has also turned out that the translational movement of the anions is faster than of cations, especially at high temperatures. Moreover, the relative cation–cation diffusion coefficients have been compared with self-diffusion coefficients obtained by means of NMR (Nuclear Magnetic Resonance) gradient diffusometry. The comparison indicates correlation effects in the relative cation–cation translational dynamics—the effects become more pronounced with decreasing temperature.
Highlights
Properties of condensed matter systems are determined by their structure and dynamics
Nuclear Magnetic Resonance (NMR) diffusometry is a wellestablished method of measuring translation diffusion coefficients—it exploits a magnetic field gradient that allows to identify the position of molecules carrying NMR active nuclei (1H and 19F typically for ionic liquids) versus time, as a result of changes in the resonance frequency
We present a thorough analysis of 1H and 19F spin-lattice relaxation data butyltriethylammonium bis(trifluoromethanesulfonyl)imide ([TEA-C4][TFSI]), taking into account all relevant relaxation pathways, especially the role of 1H–19F mutual dipole–dipole coupling
Summary
Properties of condensed matter systems are determined by their structure and dynamics. One should consider short- and long-range translation diffusion coefficients, being aware that conductivity depends on the long-range translation movement. In this context, it is worth noting that the determination of diffusion coefficients for slow dynamics poses a challenge due to the limitations of Nuclear Magnetic Resonance (NMR) gradient methods [3,4,5], referred to as NMR diffusometry. NMR diffusometry is a wellestablished method of measuring translation diffusion coefficients—it exploits a magnetic field gradient that allows to identify the position of molecules (ions) carrying NMR active nuclei (1H and 19F typically for ionic liquids) versus time, as a result of changes in the resonance frequency. The most important characteristic of NMR diffusometry is that this method provides values of self-diffusion coefficients [3,4,5], in contrast to NMR relaxometry, exploited in this work, which probes relative translation motion of ions (molecules)
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