On the importance of ideal properties to understand the dielectric relaxation of liquid mixtures

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The dielectric relaxation properties of thermodynamically ideal binary liquid mixtures are theoretically established for the case where both components are Debye liquids. A dielectric fraction is defined for weighing the contribution of each component to the overall dielectric loss. Depending on the composition and on the ratio between component relaxation times, the ideal mixture may show one or two loss peaks. It is demonstrated that it is exactly described as the superposition of two Debye functions. All these features are exemplified with model ideal mixtures that resemble closely aqueous ethanol solutions. The importance of present findings is highlighted in the context of current alternative dielectric relaxation descriptions of binary mixtures and related mixing rules for the relaxation time. A non-explicit mixing rule is worked out for the ideal mixture of two Debye liquids and it is made clear that no simple mixing rule can be devised. Further developments are suggested.