Sample preparation matters: Scanning electron microscopic characterization of polymeric membranes

This study systematically examines the influence of polymeric membrane sample preparation techniques on their morphologies and structures as revealed by scanning electron microscopy (SEM). We address the variability introduced by diverse preparation methods in research, which leads to subjective qualitative and quantitative SEM interpretations. Our investigation encompasses various preparation techniques, focusing on cryogenic sectioning—alongside SEM operational parameters including accelerating voltage and conductive sputter coating thickness. We demonstrate that surface morphology analysis via SEM is significantly affected by coating thickness and accelerating voltage, while cross-sectional images (typically, at much higher magnification) exhibit little difference in morphology. However, improper preparation can damage membranes, compromising cross-sectional imaging. We provide a detailed exploration of the cryogenic-sectioning and its effects on SEM image quality. Our findings indicate one's selection of preparation procedure can create significant biases in SEM analyses of microfiltration, ultrafiltration, and reverse osmosis polymeric membranes.