Microscopic mechanism of interfacial effects on mechanical properties of polymer nanocomposites

Interfaces play a crucial role in the mechanical properties and deformation behavior of polymer nanocomposites (PNCs). In this study, we successfully characterized the deformation behavior and stress distribution of the interface and polymer matrix at the nanoscale using the nanomechanical technique of atomic force microscopy (AFM), revealing the microscopic mechanism of the interface effects on the mechanical properties of PNCs. By comparing the interfaces of different fillers and styrene-butadiene rubber (SBR), we found that silane coupling agent-treated silica (SiO 2 ) could greatly increase the interface thickness and strength. This enhancement was not limited to the interface itself but also restricted the movement of molecular chains nearby, thereby increasing the modulus of the surrounding matrix. When the material was deformed, the high-strength interface could bear a large amount of stress, while the stresses in composites with low interfacial strength were mainly borne by the polymer matrix. This microscopic stress visualization technique enabled a deeper understanding of the correlation between the micromechanical behavior and macroscopic mechanical properties of the interface and matrix. In addition, through the quantitative analysis of the stress distribution of each phase, we proposed a multiphase composite model to describe the deformation behavior of filled rubber. We used the parallel model and the series model to calculate the composite stress of different types of filler PNCs, further reveals the importance of the interface for the mechanical properties of PNCs. Our results provided new insights for guiding the design and development of PNCs and for the study of composite interfaces.