Morphology-Based Prediction of Permeability of Asymmetric Polymeric Membranes

Hydraulic permeability is a key charactrization parameter for polymeric membranes representing overall throughput of the membrane systems and has a strong dependence on membrane morphology. The present work aims to predict membrane hydraulic permeability from Field Emission Scanning Electron Microscope images through sequential image analysis. The analysis has been carried out for different morphologies available in literature, including asymmetric as well as symmetric membranes. Permeability values predicted from image analysis are validated using experimental data reported in literature. The selection of appropriate magnification of the image has been standardized to eliminate the related errors. The relative effect of the skin layer and porous sublayer on the membrane permeability has been quantified for the first time. The effect of sublayer tortuosity on overall permeability is quantified by defining a sublayer characteristic parameter (psi), as the ratio of the tortuosity of the sublayer to the porosity of the top surface. According to the model predictions, for values of psi < 8, the effect of cross section is not very significant, whereas for higher values of psi, sublayer tortuosity is predominant. This work is an attempt to predict the transport properties of asymmetric membranes from membrane morphology using advanced image analysis techniques.