Direct Imagingof the Organic–Inorganic InterfacialTransformation

The organic–inorganic interfacial nanostructures between fillers and the matrix play a crucial role in the performance of polymer composites. Here we propose an <i>in situ</i> 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 <i>in situ</i> 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.