Molecular Dynamics Simulations of NXT-Modified Silica Dispersion Mechanism in Natural Rubber

To tackle the critical challenges of silica dispersion and interfacial compatibility in natural rubber composites, this study investigated the dispersion behavior of 3-Octanoylthio-1-propyltriethoxysilane (NXT)-modified silica in natural rubber (NR) and the mechanism by which it affects mechanical properties. Three distinct models were constructed: an NR model, an NR composite model containing unmodified silica (SiO2), and an NR composite model containing NXT-modified silica (NXT-SiO2). The radial distribution function (RDF) was used to characterize the dispersion of fillers. The results of filler–filler interactions revealed a reduction in the number of hydrogen bonds between NXT-SiO2 fillers, weakening the filler network strength and enabling NXT-SiO2 to exhibit excellent dispersion. The results of filler–rubber interactions indicated that NXT-SiO2 exhibited stronger interaction forces and compatibility with natural rubber compared to SiO2. To verify the effect of NXT-SiO2 on the mechanical properties of natural rubber composites, uniaxial tensile deformation via molecular dynamics simulation was performed on the three models. The simulation results show that the addition of NXT-SiO2 significantly increases the tensile strength and fracture strain of the composite material, markedly enhancing its mechanical properties. Further studies indicate that NXT-SiO2 improves the overall mechanical properties of the material by altering the distribution of local natural rubber chains. This work elucidated the intrinsic mechanisms—on a molecular level—by which NXT silane coupling agent modifications enhance the dispersion of fillers and improve the mechanical properties of rubber, thereby providing a theoretical basis for the design of high-performance rubber composites.