| Autor: |
Weingartner, H., Nadolny, H. G., Kashammer, S. |
| Zdroj: |
The Journal of Physical Chemistry - Part B; June 3, 1999, Vol. 103 Issue: 22 p4738-4743, 6p |
| Abstrakt: |
We report on the complex dielectric permittivity up to 20 GHz of solutions of tetrabutylammonium bromide in carbon tetrachloride at salt concentrations between 0.01 and 1 mol dm-3, where the molar conductance increases with concentration up to molten saltlike conductances. At concentrations below about 0.1 mol dm-3, the frequency dependence of the permittivity shows Debye behavior with a single relaxation time, as would be expected for the reorientation of dipolar ion pairs. The static permittivity monotonically increases with concentration. Assuming dipolar processes as the major contributors to the dielectric spectra, Kirkwood's theory yields correlation factors which rapidly decrease with increasing salt concentration, indicating strong antiparallel correlations of dipole orientations even at concentrations as low as c = 10-4 mol dm-3. Above c = 0.1 mol dm-3 the spectra broaden rapidly, while the viscosity remains low. In this range the spectra are well-represented by a Cole−Cole expression with a mean relaxation time essentially proportional to the viscosity. We suggest that at higher concentrations part of the polarization arises from a Debye−Falkenhagen-type mechanism caused by the asymmetry of the ion atmosphere in the applied field. The increasing importance of this contribution appears to result from the dissociation of ion pairs by interaction with the remainder of the screening ionic fluid, which eventually leads to a transition to molten saltlike structures. |
| Databáze: |
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