Interactions and dynamics in electrolyte solutions by dielectric spectroscopy

Abstract

Despite its immense abilities to quantify many aspects of ion-ion and ion-solvent interactions, dielectric relaxation spectroscopy (DRS) has long been neglected as a tool for the investigation of the structure and dynamics of electrolyte solutions. The reasons for this are briefly discussed and it is shown that many of the difficulties associated with this technique have been overcome in recent years by technological developments. Representative applications of DRS to the investigation of ion solvation and ion association in electrolyte solutions of chemical, industrial, geochemical and biological interest, including room temperature ionic liquids and polyelectrolyte systems, are discussed. The advantages of linking DRS measurements to information obtained from other experimental techniques and from computer simulations are highlighted.

Do H-bonds explain strong ion aggregation in ethylammonium nitrate + acetonitrile mixtures?

“…22 On the other hand, from the temperature dependence of the relaxation time of pure AN a value of C = 0.119 was obtained, 18 which is virtually identical to the theoretically predicted friction factor for rotation under slip hydrodynamic boundary conditions, C slip = 1 À f > 2/3 = 0.118. 45 As argued previously, 13,24 this indicates that for dipolar aprotic solvents, like AN, the rise of solution viscosity with salt/IL content is essentially due to mixing particles of different size, i.e. a mere blocking effect.…”

“…13 For electrolyte solutions decreasing Z ib with increasing salt concentration is common and explained in terms of solvation-shell overlap. 24,50 This certainly also applies to the dilute IL solutions. The breakpoint at x EAN E 0.2 may be related to the pronounced formation of contact ion pairs (CIPs) for this system (see below) which should be associated with at least partial desolvation of the CIPs due to charge neutralization.…”

“…Dielectric relaxation spectroscopy (DRS) probes polarization as the linear response of the sample to a time-dependent electric field, which corresponds to fluctuations of the macroscopic dipole moment 24,31 In the frequency domain, the experimentally accessible quantity is the complex generalized permittivity…”

“…In this procedure k was treated as an adjustable parameter with the experimental data as the starting values to account for fringing-field contributions arising from geometrical imperfections of the VNA probes. 24 In order to extract molecular-level information from DR spectra an appropriate relaxation model has to be found for the experimental data. Dipole fluctuations taking place at microwave frequencies for liquids at room temperature are typical relaxation processes.…”

Ion Segregation in Aqueous Solutions

“…The concentration is increased to 76% ± 2% by the addition of KF, to 71% ± 2% by the addition of K 2 HPO 4 , and to 79% ± 2% by the addition of K 2 CO 3 . The small amount of hydroxyl anions produced by the hydrolysis of F − , CO 3 2− , or HPO 4 2− is not responsible for the effect (faster energy transfer) observed. By contrast, adding 5 mol KOD into the thiocyanate solution slows down the energy exchange among the thiocyanate anions, similar to the effect of adding 5 M KI.…”