SEM imaging of membranes: Importance of sample preparation and imaging parameters

SEM imaging has been used by researchers to characterize the membrane properties. However, limited information is generally reported regarding the sample preparation and imaging parameters used, making it difficult to compare results from different studies. The present study focuses on the influences of sample preparation and imaging parameters on the observed membrane surface properties obtained from SEM images. Polymeric membranes were prepared with different coating metals (gold, gold–palladium and iridium) and coating thicknesses, and imaged with different imaging parameters (magnification, detector, sample orientation). Image analysis was done using a custom Matlab application. The effects were observed both qualitatively and quantitatively (pore size/shape and porosity). All of the sample preparation and imaging parameters affected the observed membrane properties of interest. In general, the membrane properties were less sensitive to the parameters when membranes were coated with iridium than with gold or gold–palladium. Iridium should be used as the coating metal in the studies where coating thickness and/or, one or more imaging parameters need to be varied. The results suggest the need of a standardized SEM procedure for membrane characterization, and clear reporting of the parameters used in any SEM study, to enable appropriate comparison of the results obtained in different studies.