Toshio Nishi

Characterization of nanoscale mechanical heterogeneity in a metallic glass by dynamic force microscopy.

We report nanoscale mechanical heterogeneity of a metallic glass characterized by dynamic force microscopy. Apparent energy dissipation with a variation of ~12%, originating from nonuniform distribution of local viscoelasticity, was observed. The correlation length of the heterogeneity was measured to be ~2.5 nm, consistent with the dimension of shear transformation zones for plastic flow. This study provides the first experimental evidence on the nanoscale viscoelastic heterogeneity in metallic glasses and may fill the gap between atomic models and macroscopic glass properties.

Polymer nanotechnology applied to polymeric nano-soft-materials

We have been developing new techniques to evaluate polymer nano-alloys and nano-composites. This nanotechnology can be classified into nano-three dimensional (3D) measurement, nano-physical properties evaluation systems, and nano-spectroscopy. As for the nano-3D measurement, we developed polymer oriented energy-filtered 3D transmission electron microscopy. With this method, we can access important 3D structural and elemental information that cannot be obtainable from ordinary TEM. Nano-physical properties evaluation systems were also established by developing atomic force microscopy force-distance curve measurement. The distribution of mechanical properties such as Youngs modulus and adhesive energy was quantitatively obtained on high lateral resolution. These methods give new pieces of information unobtainable by the conventional techniques on polymer nanotechnology. Several results are shown here.

The interface dynamics of bicontinuous phase separating structure in a polymer blend

The time evolution of the phase separating pattern during the spinodal decomposition (SD) of a specimen was observed at the same volume of the specimen using X-ray computerized microtomography (X-ray CT). A careful examination of time-dependent three-dimensional (3D) images revealed that bridge-like domains played an important role in the phase separation dynamics. In the course of the SD, some bridge-like domains became thicker, while the others became thinner. It was found that the pressure difference across the interface, which is quantified through the mean curvature of the interface, influences such interface dynamics.