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(Your abstract must use Normal style and must fit in this box. The abstract should be written in English and should be around 1000 words long, i.e., 2 pages excluding title, authors & affiliations, keywords and references. Authors are encouraged to show important figures/tables etc in the abstract so as to make a full presentation.) The fabrication of most polymeric nanofiltration membranes is currently more of an ‘art’ than a ‘science’, as there is no established relationship linking the fabrication variables, material characteristics when in use (or even wetted) with the performance (separation) characteristics. Consequently, the overall objective of this project is to determine the relationship between nanofiltration membrane fabrication variables, the resulting membrane microstructure when wetted and the characteristics of the separation (flux and rejection) that result from that microstructure. Polyimide nanofiltration membranes intended to be used for organic solvent nanofiltration are the main focus of the current work. Such membranes have been found to be effective for applications such as: the separation of solvents from lube oil and separation of aromatics, recycling homogeneous catalysts and bases, separating chiral diastereomers and green organic synthesis. The membranes in this study were cast by phase inversion from P84 co-polyimide (HP polymer GmbH) at 250 m thickness on a non-woven backing layer, varying formation parameters (dope solvent, solvent evaporation time, polymer concentration and post formation heat treatment temperature). The innovation in this work is in using wetted microstructural techniques to determine the macroscopic and microstructural changes of the membranes both from different casting conditions, wetted in different solvents before and after use, primarily using an environmental scanning electron microscope (ESEM; FEI Quanta 200F) and differential interference contrast (DIC) microscopy (Nikon Eclipse 80i, Nikon Instruments Inc., NY), with sectioning for the latter using a sledge microtome (Leica Microsystems Model SM2000R, Germany). This is compared to typical ‘dry’ membrane analysis by Field Emission Scanning Electron Microscopy (SEM; Philips XL30S Field Emission Gun). Both ESEM and DIC imaging showed clear differences between dry and wetted microstructures that correlate to membrane formation parameters. When saturated in different organic solvents, these membranes exhibit considerable structural swelling that significantly changes the microstructure (Figures 1 and 2) compared to the dry membrane microstructures (e.g. Figure 1a and 3).

Determining Wetted Membrane Microstructures using ESEM and DIC Microscopy and their Implications to Membrane Performance