Investigation on the aggregation behavior and mechanical properties of silica-filled natural rubber composites: A coarse-grained molecular dynamics study

Understanding the particle aggregation behavior in filled rubber is crucial for developing high-performance composite materials. Herein, the effect of the spatial distribution of silica nanoparticles, the length of matrix molecular chains, and the crosslinking of the matrix on the mechanical properties of natural rubber (NR) composites were systematically investigated using coarse-grained molecular dynamics (CGMD) simulations. The results show that with the increase in the degree of silica nanoparticle aggregation, the stress level of the filled rubber in the small deformation stage is significantly increased, but in the large deformation stage, it is significantly reduced. The former can be attributed to the supporting effect of the high strength and rigidity of the particle network in the small deformation stage, while the latter can be attributed to the gradual failure of the particle network in the large deformation stage and the weakening of the adsorption of the particles on the rubber molecular chain. Moreover, it was found that longer molecular chains reduced particle aggregation by enhancing particle encapsulation and interface interactions, while crosslinked networks promoted aggregation behavior by restricting particle mobility through a cage structure. To explain in depth the inherent enhancement mechanism of nanoparticle-filled rubber, microstructure property analysis, such as mean square displacement, interaction energy, and bond orientation, has been implemented and discussed.