Soret vector for description of multicomponent mixtures

The Soret effect describes the transport of constituent species in multicomponent mixtures that occurs due to a temperature gradient. This cross-coupling effect of heat and mass transfer has been successfully examined in binary liquid mixtures, while experiments with ternary mixtures are rare as they impose significant difficulties. We introduce a new and innovative concept, the Soret vector, for the characterization of Soret driven separation in ternary mixtures. The presentation of the component separation in the vector form offers several advantages: (i) to predict the Soret sign of a ternary mixture from knowledge of the Soret coefficients in binary subsystems; (ii) to control consistency of measured coefficients, this is especially important when results are obtained using different instruments and methods; (iii) to determine in which regions and which components cause the greatest separation; (iv) to identify the regions where the Soret separation is inaccessible for optical techniques or gravitationally unstable. We demonstrate these features by exploring ternary mixtures of different origins: (a) nearly ideal mixture composed by THN-IBB-nC12 when Soret coefficients in binary subsystems (S-T(bin)) are positive, (b) non-ideal mixture containing water and ethanol TEG-Wat-EtOH when S-T(bin) are positive and negative and (c) Tol-MeOH-Ch mixture containing demixing zone with positive and negative Sbin T. Our approach provides a promising systematic framework for the future research of an important and challenging problem of thermodiffusion in multicomponent liquids.

Automated summary

The Soret effect explains the transport of constituent species in multicomponent mixtures due to temperature gradient, and the introduction of the Soret vector presents a new concept for characterizing Soret-driven separation in ternary mixtures. The vector form offers advantages such as predicting Soret sign, controlling coefficient consistency, determining components causing separation, and identifying regions where Soret separation is inaccessible for certain techniques. This approach provides a systematic framework for future research on the challenging problem of thermodiffusion in multicomponent liquids.