Dielectric Behaviour of Ice Microcrystals: A Study Versus Temperature

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Abstract
Dispersions of ice microcrystals were obtained from the breakdown of supercooling of water-in-oil type emulsions whose disperse phase was either resin-exchanged water or aqueous solutions of NH4Cl. Their complex permittivity ε⋆ = ε´–jε˝ was studied versus temperatureT,up to the melting point of ice microcrystals, by means of an automatically balancing admittance bridge (General Radio 1680 A) working at 400 Hz and 1 kHz, The plots ε´(T), ε˝(T) and ε˝(ε´) reveal that these systems exhibit two distinct dielectric relaxations located on either side of a temperatureTmwhich was found to be equal to about — 20°C in the case of water and lower than — 20°C in the case of aqueous solutions of NH4Cl. The relaxation located in the lower temperature range arises from the Debye dipolar absorption of ice while the other one could be related to structural changes occurring within the lattice of ice asTapproaches its melting point. These results are consistent with those obtained by investigating versus frequency the dielectric behaviour of ice monocrystals at discrete sub-zero temperatures close to their melting point.