Figure 4

FESEM images of a the cross-section of PAA fabricated in 1 wt% H₃PO₄ under 0°C and 180 V for 10 min and bent before testing, b the low-magnification image of (a), (c) and (d) the fracture sections of PAA after cutting with a pair of scissors and scratching the surface with a diamond knife, respectively. The PAAs in c and d are fabricated in 5 wt% H₃PO₄ at 15°C for 30 min without second anodization