Recent developments of morphological characterization in nano-composite materials by electron microscopy

In order to truly understand various interesting properties of soft materials, it is crucial to directly visualize their morphologies both in quiescent state and under deformation. The interfacial region between fillers and polymer matrix, the interphase regionfor short, is believed to be one of the key morphological elements in nanocomposite materials. Direct visualization of such interphase region has been a subject for many years. Although transmission electron microscopy (TEM) is a powerful tool to visualize nano-scale polymeric morphologies, however, because the interphase region consists of the same polymeric species as the matrix, it is invisible under TEM. Atomic force microscopy (AFM), on the other hand, clearly demonstrates regions with higher elastic modulus (than the matrix) around the fillers, indicating the existence of the interphase region. However, because the mechanical properties can be easily affected by the structures underneath the measurement points, the high elastic regions around the fillers may not truly reflect the interphase region. Thus, we used transmission electron tomography, a nano-scale three-dimensional (3D) visualization method, to investigate the internal 3D structure of rubber nano-composite at exactly the same placeas the AFM force measurements. In doing so, it became possible to accurately determine the interphase regions for the first time.
Morphological characterization under deformation is another crucial factor for fundamental understanding of mechanical properties of nano-composites. We have developed a tomography holder for in-situ tensile deformation. Because both ends of specimen are stretched simultaneously at the same stretching rate in this new holder, drifting of field of view for TEM observations becomes minimum. The newly-developed holder was used to observe deformation processes of a rubber nano-composite. Details of the structural deformation will be discussed at the conference time.