Direct Imaging of the Organic-Inorganic Interfacial Transformation.

The organic-inorganic interfacial nanostructures between fillers and the matrix play a crucial role in the performance of polymer composites. Here we propose an cryogenic transmission electron microscope technique (cryo-TEM) approach to directly observe the organic-inorganic interfacial transformation in a toluene diisocyanate (TDI)-based polyurethane composite during its synthesis process. Elliptical protrusions growing radially outward from the filler surface, which serve as the critical intermediate nanostructures of the interface layer, are observed by cryo-TEM, indicating that the interface layer is formed through a curing reaction of the prepolymer molecules anchored on the filler surface. Both decreasing filler sizes and adding coupling agents can enhance the interfacial interactions. The addition of 0.05 wt % coupling agent increases the interface thickness from 83.93 to 129.31 nm and improves the fracture toughness of the composite by 75.1%. These findings provide new insights for rationally designing interfacial nanostructures and high-performance polymer composites.