Electron microscopy for polymer structures

This paper reviews recent advances and perspectives of electron microscopy and its application to polymer hierarchical structures. Of the various kinds of hierarchical polymer structures, we placed particular emphasis on polymer nanocomposites and polymer crystals based mainly on our recent results. In those nanocomposites, the chemical bonding between the nanometer-size fillers and rubber matrix, a key contributor to the mechanical properties of the material, has been investigated by combining scanning transmission electron microscopy (STEM) with electron energy-loss spectroscopy (EELS). The position-dependent EELS spectrum with high spatial resolution of STEM successfully provided revealed the presence/absence of the chemical bonds across the interface. The mechanical properties and fracture mechanism of nanocomposites have been studied by combining structural observations made using transmission electron microscopy (TEM) with simulations. They have been further investigated using in situ TEM with a newly designed stretching holder, in which morphological changes, including cavity formation, were visualized and analyzed in terms of local strain distribution. The fracture processes of nanocomposite have been observed at nanometer resolution. The fundamental reinforcement mechanisms have been elucidated from morphological studies of nanocomposites under tensile deformation and during the fracture process. Moreover, nano-diffraction imaging, a position-resolved electron diffraction imaging with STEM, has been applied to a polymer crystal to evaluate the orientation of lamellar crystals at nanometer resolution. All these recent successes with radiation-sensitive polymer materials stemmed from developments made in electron optics and super-sensitive cameras used for advanced electron microscopy.