Measurement of the Soret and diffusion coefficients for benchmark binary mixtures by means of digital interferometry

We report on the development of the optical digital interferometry (ODI) technique for measuring diffusion and Soret coefficients. The unique feature of this method is that it traces the transient path of the system in the entire two-dimensional cross section of a cell. In this way, it is applicable not only for measurements of Soret coefficients, but also for studying diffusive transport mechanism and convection. Presently, this method is not widely used and, in our view, not because of fundamental limitations but rather due to a lack of properly developed postexperimental procedures of the raw data analysis. Thus, in this paper our attention is focused on the successive analysis of different steps: the fringe analysis, the choice of reference images, the thermal design of the cell, and multiparameter fitting procedure. Using the ODI technique, we have measured the diffusion and the Soret coefficients for three binary mixtures composed of dodecane (C12H26), isobutylbenzene, and 1,2,3,4-tetrahydronaphtalene at a mean temperature of 25 degrees C and 50 wt. % in each component. These measurements were compared with their benchmark values and show an agreement within less than 3%. (C) 2011 American Institute of Physics. [doi:10.1063/1.3546036]