Measurement of the diffusion coefficient of miscible fluids using both interferometry and Wiener's method

Measurements of the diffusion coefficient of two miscible liquids are repor ted. The liquids at e various combinations of pure silicone oils and those to which small amounts of solvents are added to control the difference in d ensity between the fluids. The liquids were placed in a quartz cell such th at the interface is initially horizontal. As the fluids diffuse, the profil e of the index of refraction near the interface is time dependent and is re lated to the local concentration of the diffusing fluids. The concentration gradient profile was measured by a shearing interferometer incorporating a Wollaston prism, as well as Wiener`s method. In the latter technique, a 45 degrees light sheet was passed through the test cell. and the local deflec tion of the light beam was measured. The average diffusion coefficient was obtained by analysis of the measured concentration gradient profile, assumi ng that the diffusion process is one-dimensional and is characterized by a constant value of the diffusion coefficient.