Reverse osmosis modules comprised of composite polymer membranes represent a leading technology in desalination and purification of brackish water.  Nanoporous polymeric membranes are key for prefiltering of such reverse osmosis systems, as well as for purification of biopharmaceutical products, such as monoclonal antibodies.  The field has relied on intricate control of membrane properties through systematic perturbations to membrane chemistries and processing, yet many fundamental questions remain on the mechanisms that govern water transport and separations. Through collaborative work between industry and academia, we have leveraged advances in multi-modal electron microscopy to generate new insights on membrane structure and function.  For example, we have combined the focused ion beam with scanning electron microscopy through serial sectioning to reconstruct a 3D representation of ultrafiltration membranes using for virus removal from biopharmaceutical streams.  These reconstructions reveal key morphological features that govern virus capture and sensitivity to process conditions (e.g. pressure).  In addition, we have combined energy-filtered transmission electron microscopy with electron tomography from scanning transmission electron microscopy images to map the variation in density of polyamide films used in reverse osmosis membranes.  Modeling flow through these 3D maps reveal how the distribution of mass affects flow patterns and overall flux, and thereby resolves long-standing questions on the mechanisms that govern aqueous transport through dense polymer films.  Furthermore, we image membranes challenged with model and common foulants, to ascertain initial conditions and mechanisms for degradation of filtration performance. Key to the work is the collaboration between industry and university researchers to address crucial challenges in membrane science.

Mapping nanoscale inhomogeneity to reveal flow through polymer membranes

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