Dielectric Relaxation of Aqueous NaCl Solutions
Richard Buchner, Glenn T. Hefter, and Peter M. May
J. Phys. Chem. A, in press
Abstract
The complex dielectric permittivity of aqueous sodium chloride solutions
has been determined in the frequency range 0.2 <= n/GHz
<= 20 with a commercial dielectric measurement system based on a
vector network analyzer. NaCl solutions 0.1 <= m/mol·kg-1 <= 5 (mass fraction 0.005 <= w <= 0.23) were investigated at 5°C, 20°C, 25°C, and
35°C. An improved calibration procedure of the dielectric
measurement system for conducting samples was developed. The complex
permittivity spectra have been represented by a Cole-Cole
relaxation-time distribution. Where possible, the obtained fitting
parameters - static permittivity e, relaxation time t and
distribution parameter a - are compared with literature data
to assess the performance of the instrument which was found to be
comparable to that of time domain and waveguide systems. Effective
solvation numbers were deduced from the effect of NaCl concentration on
e. The data suggest that in addition to the irrotational bonding of
water molecules by Na+ ions, kinetic depolarization under slip
boundary conditions determines the solution permittivity. A three-state
model is proposed to describe the concentration dependence of t.
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(c) 1998 Herbert Poepke
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