Determining diffusion, thermodiffusion and Soret coefficients by the thermogravitational technique in binary mixtures with optical digital interferometry analysis

Abstract In the present work, interferometric unsteady state analysis of the thermogravitational technique is for the first time attempted in a microcolumn. In this way, three transport coefficients, diffusion, thermodiffusion and Soret coefficients can be obtained in a single experiment. Two different models — one from the Furry-Jones-Onsager theory and the other with the ‘forgotten effect’ included — have been tested for six different binary mixtures. These mixtures are the three binary pairs of the Benchmark of Fontainebleau— tetrahydronaphthalene-isobutylbenzene (THN-IBB), tetrahydronaphthalene-dodecane (THN-nC12) and isobutylbenzene-dodecane (IBB-nC12)—toluene-methanol dimethyl sulfoxide-water (DMSO-H20) and dimethyl sulfoxide-deuterated water (DMSO-D20). The first three benchmark binary mixtures are used to validate the inteferometric technique and also to establish when it is reasonable to treat a mixture as ideal, without considering the forgotten effect. After that, the three remaining mixtures are deeply analysed. In the end, the isotopic effect in the Soret coefficient will be highlighted through the DMSO-H20 and DMSO-D20 mixtures.