An Interferometric Technique for Measuring Binary Diffusion Coefficients

An accurate interferometric technique for the measurement of Fick binary diffusion coefficients is described. The technique employs a Mach-Zehnder interferometer together with a high-speed stroboscope and flash-tube light source and a drum camera as a recording system. Successive concentration profiles are recorded in a modified, transient, one-dimensional Arnold diffusion model. A relative-time, relative-position method is used to analyze the interferograms, thus eliminating the uncertainties regarding the absolute diffusion time and exact position above the liquid surface in the diffusion cell as well as the overall mass transfer rate. This technique yields experimental values of the diffusion coefficient with an estimated accuracy of 1/2 percent and reproducibility of approximately ±1 percent. The binary diffusion coefficients for ten materials, four polar and six nonpolar, diffusing in air are presented. Of these, five have been studied by other investigators. The other five have not been previously reported in the literature.