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Two-color optical measurements of thermodiffusion in ternary mixtures frequently suffer from ill-conditioned contrast factor matrices, whose inversion leads to very large experimental errors. In this contribution, we show how the error amplification can be avoided in situations where a priori knowledge about the directions of the eigenvectors of the diffusion matrix is available. We present optical beam deflection experiments on solutions of the polymer polystyrene of Mw = 4880 g/mol in a mixed solvent of toluene and cyclohexane. In this system, the two diffusion eigenvalues differ by almost one order of magnitude. The large eigenvalue can be attributed to the interdiffusion of the two solvents and the small one to the polymer diffusion relative to the mixed solvent. The pre-selection of the eigenvectors renders the method stable against fluctuations of the experimental parameters. Both the diffusion and the Soret coefficients attributed to the two modes agree very well with the respective values of corresponding binary mixtures. [ABSTRACT FROM AUTHOR]

Thermodiffusion in ternary mixtures is considered prototypic for the Soret effect of truly multicomponent systems. We discuss ground-based measurements of the Soret coefficient along the binary borders of the Gibbs triangle of the highly polar and hydrogen bonding ternary DCMIX3-system water/ethanol/triethylene glycol. All three Soret coefficients decay with increasing concentration, irrespective of the choice of the independent component, and show a characteristic sign change as a function of temperature and/or composition. With the exception of triethylene glycol/ethanol at high temperatures, the minority component always migrates toward the cold side. All three binaries exhibit temperature-independent fixed points of the Soret coefficient. The decay of the Soret coefficient with concentration can be related to negative excess volumes of mixing. The sign changes of the Soret coefficients of the binaries allow to draw far-reaching conclusions about the signs of the Soret coefficients of the corresponding ternary mixtures. In particular, we show that at least one ternary composition must exist, where all three Soret coefficients vanish simultaneously and no steady-state separation is observable. [ABSTRACT FROM AUTHOR]

Ternary mixtures play an important role as model systems for the understanding of non-isothermal transport phenomena in liquids. The DCMIX project of ESA aims to establish reliable reference data for the Soret effect in ternary liquids and serves as a nucleus for ground based work. Up to now, three DCMIX campaigns have been carried out aboard the International Space Station ISS. The investigated ternary mixtures are dodecane/isobutylbenzene/tetralin (DCMIX1), methanol/toluene/cyclohexane (DCMIX2) and water/ethanol/triethylene glycol (DCMIX3). DCMIX4 is scheduled for 2018. The microgravity experiments are performed by means of the SODI instrument, a digital Mach-Zehnder interferometer. In order to fully characterize a ternary mixture, it is necessary to extract six independent parameters from the measured data, which is particularly difficult in case of similar diffusion eigenvalues. A detailed analysis shows that, nevertheless, stable values for the thermodiffusion and the Soret coefficients can be obtained. Additional errors arise from the inversion of the contrast factor matrix, which is frequently ill-conditioned. Besides first data from the DCMIX3 microgravity experiments, which have been coordinated by our group at the University of Bayreuth, we review some important results from the DCMIX1 campaign. These include a benchmark with the participation of a number of different groups and the measurement of a complete data set for the DCMIX1 system in the laboratory. The latter results can be rationalized on the basis of the so-called thermophobicity concept previously introduced for binary mixtures. • The DCMIX project aims at convection-free thermodiffusion data for ternary mixtures • Experiments aboard the ISS by means of a two-color digital interferometer (SODI) • Very good agreement between microgravity and ground experiments • First results underline the critical importance of precise optical contrast factors [ABSTRACT FROM AUTHOR]

• (Thermo)-Diffusion coefficients in Neopentylglycol-Camphor alloys have been measured. • Thermodiffusion effects during holding of liquid NPG-DC alloys have been simulated. • A special scenario that mimics ISS experiment has been simulated. • For typical parameters, small deviations from homogeneous liquid were obtained. We present results from a combined experimental and numerical approach to estimate the impact of thermodiffusion in the liquid phase of the binary system neopentylglycol-(D)camphor (NPG-DC) during the pre-solidification holding period of experiments on the International Space Station (ISS) in reduced gravity conditions. The Soret coefficient S T , diffusion coefficient D and thermodiffusion coefficient D T have been measured by means of the optical beam deflection technique using mixtures close to the eutectic composition of the alloy (0.547 wt frac. NPG) in the composition range of 0.522–0.581 wt frac. NPG and at different temperatures above their respective liquidus temperatures. Numerically, we implemented a one-dimensional time-dependent thermodiffusion equation to describe the composition evolution during the holding pre-solidification phase in the NPG-DC alloy in a given temperature gradient. The validated model was then applied to the more complex case of spatially changing thermal gradients, which are expected in the experimental facility used onboard the ISS. Numerical simulations estimating a maximum effect of thermodiffusion showed a small but clear effect. Using the previously determined transport coefficients and a holding phase of 10 hours, a change of the NPG concentration of less than 7% of the initial composition was obtained for the given set-up. Even if the real thermodiffusion effect is expected to be smaller, this lateral inhomogeneity in concentration has to be taken into consideration in the microgravity experiments. [ABSTRACT FROM AUTHOR]