Determination of a diffusion coefficient in a membrane by electronic speckle pattern interferometry: a new method and a temperature sensitivity study

In this work, a method has been developed to easily determine the effective diffusion coefficient (De) of a solute in a permeable membrane using electronic speckle pattern interferometry. Fringes are introduced parallel to the direction of diffusion during the diffusion process and De can be calculated by simple measurements on the interference pattern. For a fast and convenient determination of De, a mathematical expression has been derived from the analytical solution of diffusion in two media separated by a resistance. The De obtained when fringes are introduced is in agreement with that obtained when fringes are not introduced. The effect of temperature variation on the optical path of the reference and the object beams has also been investigated. The error introduced into the calculation of De, when the temperature oscillation is not taken into account, has been compared for the case when fringes are not introduced during the diffusion experiment and the case when fringes are introduced. In the first case, the relative error can be greater than 100%. Interestingly, in the latter case, the error caused by temperature oscillation is considerably reduced, and no error is introduced if the temperature changes homogeneously over the whole diffusion cell used for the diffusion experiment.