Membrane characterization by optical methods: Ellipsometry of the scattered field

The fouling phenomenon is the major drawback of membrane processes. To be able to localize membrane fouling could be a real progress in the fouling understanding and the optimization of membrane regeneration step. For that, the membrane structure parameters must be taken into account. Classical techniques; such as displacement, tracer retention and microscopy; provides only information about the pore size of the skin layer and the thickness of the successive layers. The angle-resolved light scattering technique and the analysis of the scattered wave polarization state via ellipsometry of angle resolved scattering (EARS) are used to characterize more accurately membrane structure and to discriminate microfiltration and ultrafiltration ceramic membranes. The main objective of this study is to show the potential of these recent optical techniques that are very little known in the domain of membrane processes. First, the techniques of light scattering and ellipsometry will be reviewed, and then the results obtained for several unused ceramic membranes with different cut-offs will be detailed. The low resolution analysis clearly shows that the observed light scattering comes essentially from the bulk, but fails to differentiate between cut-offs. High resolution angle-resolved measurements make it possible to obtain a specific signature to each cut-off. The higher the porosity, the greater the angular variations of the polarimetric phase shift. Simulations performed by applying a rigorous method for the resolution of Maxwell's equations will validate these observations.