Oscillations, Waves, and Interactions - GWDG

Multistep association of cations and anions 347
Figure 12. Real part ɛ ′ (ν) and negative imaginary part ɛ ′′ (ν) of the complex dielectric
spectrum of water (+) and of a 0.1 mol/l solution of Al2(SO4)3 in water (◦, •) at 25 ◦ C [20].
Open symbols indicate data from a difference method applied in time domain measurements,
closed symbols show data from frequency domain techniques. Lines are graphs of the Debye
function (Eq. (3)) with subscript ”w” refering to water and of the two-Cole-Cole-term
function defined by Eq. (15).
in the solvent contribution to the complex dielectric spectrum are due to interactions
of the water molecules with the ionic species. A remarkable feature in the spectrum
of the electrolyte solution (Fig. 12) is the additional low-frequency relaxation with
amplitude ɛ(0) − ɛ1 and relaxation frequency (2πτ2) −1 . This relaxation reveals directly
the existence of dipolar ion complex structures with life times larger than the
reorientation times.
The relaxations in the solution spectrum are subject to a small distribution of
relaxation times. The spectrum, without conductivity contribution, has been repre-