TFC membranes fabricated using the PAN-O, PAN-H, and PAN-A substrates via IP were characterized by SEM; the SEM images of the top view with varied scales and cross-sectional view are demonstrated in Figures 3a and 3b, respectively. The upper panel of Figures 3a shows the top views at a lower magnification. It evidently indicates that the IP film was not firmly ‘locked’ by the surface of the PAN-A substrate and irregularly split into smaller pieces with curved or folded edges. In contrast, both the PAN-O and PAN-H substrates yielded a relatively uniform and ‘undamaged’ IP layer, whose typical ridge and valley substructures3,40 are resolved by zooming in on the surface of the IP layer (the lower panel of Figures 3a). The SEM image with a higher magnification also reveals similar substructures of the IP layer peeling off from the PAN-A substrate.