“…There are many effective methods to characterize the evolution of structure and properties, such as X‐ray diffraction (XRD),8–12 viscosity,2, 6, 13 FTIR,6, 13–15 laser scanning confocal microscopy,2 electron spin resonance spectroscopy,16 energy dispersive X‐ray spectroscopy,1 small angle X‐ray scattering (SAXS),17, 18 and scanning electron microscopy (SEM) 13, 19. As to PPTA fiber, viscosity, XRD, and FTIR are proved to be effective methods to study the hydrothermal aging.…”