BINARY DIFFUSION STUDIES WITH A WEDGE INTERFEROMETER

By conducting a free-diffusion experiment in a thin wedge formed by two partially reflecting glass plates, binary diffusion coefficients in liquid systems can be determined from an analysis of the interference patterns which are induced when this optical wedge is illuminated by monochromatic light. The accuracy, limitations, and potential problems associated with this technique are investigated, and innovations in experimental techniques, cell design, and data analysis are disclosed. Measurements of the concentration-dependent diffusion coefficient for the binary system of sucrose-water at 25° demonstrate that diffusivity data accurate to 3% or less can be obtained with the wedge interferometer technique. This study shows that it is deceivingly easy to produce data with a wedge interferometer but rather difficult to obtain accurate data because there are several points in this type of diffusion experiment where significant errors can be introduced if certain precautions are not taken.