Fig. 6

SEM fractographic study after delamination. a Schematic drawing illustrating a GO film delaminated after lap-shear test, which generate two fractured surfaces denoted as front and back sides. For the films made from pristine, un-etched GO sheets, SEM images reveal b, c cellular patterns of “upward” wrinkles on one side of the delaminated surface, and d, e complementary “downward” wrinkles on the other side. For the films made from 5-h-etched porous GO sheets, f–i both sides have terrace-like structure with some flakes being nearly pulled out. For the films made from a mixture of pristine and 25 wt% of 5-h-etched porous GO sheets, j–m the fractured surfaces show both wrinkles and terraces. The blue dashed lines in the low-magnification images (b, d, f, h, j, l) indicate the area of epoxy adhesive behind the delaminated GO. The higher-magnification images (c, e, g, i, k, m) are taken in the areas indicated by the white boxes in the corresponding low-magnification images