Zusammenfassung
Dielec. spectra over the frequency range of 0.2 .ltorsim. ν/GHz ≤ 89 were measured for the room-temp. ionic liq. 1-N-ethyl-3-N-methylimidazolium ethylsulfate ([emim][EtSO4], IL) and its mixts. with dichloromethane (DCM) at temps. of 5 ≤ .vtheta./°C ≤ 65 and 25° resp. The spectra of the neat IL at all temps. and those of the mixts. could be satisfactorily fitted by assuming three relaxation ...
Zusammenfassung
Dielec. spectra over the frequency range of 0.2 .ltorsim. ν/GHz ≤ 89 were measured for the room-temp. ionic liq. 1-N-ethyl-3-N-methylimidazolium ethylsulfate ([emim][EtSO4], IL) and its mixts. with dichloromethane (DCM) at temps. of 5 ≤ .vtheta./°C ≤ 65 and 25° resp. The spectra of the neat IL at all temps. and those of the mixts. could be satisfactorily fitted by assuming three relaxation modes, a Cole-Cole process at lower frequencies and two Debye processes at higher frequencies. Consistent with previous studies, detailed anal. of the first (lowest-frequency) process, centered at 0.2-2 GHz depending on temp. and compn., indicated that it is mainly due to the reorientation of the dipolar [emim]+ cations. At high dilns. in the mixts. (xIL .ltorsim. 0.2), contact ion pairs also contribute to this mode. The second mode at ∼8 GHz, which is absent from the dielec. spectra of previously studied imidazolium salts and their mixts. with DCM, is assigned to reorientation of the dipolar [EtSO4]- anions. The highest-frequency mode (located at ∼80 GHz) in the mixts. is a composite of low-energy intermol. vibrations originating from the IL and the rotational diffusion of DCM mols. Detailed anal. of the spectra reveals marked orientational correlations of the IL components, with the cation dipoles showing a strong preference for parallel and the anions showing preference for antiparallel arrangements. These effects are the probable cause of the unusually high dielec. const. of [emim][EtSO4]. The structure of the IL appears to be maintained up to quite high dilns. (xIL ≥ 0.2) in DCM.
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