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.