Tailoring Interfacial Properties in Polymer–Silica Nanocomposites via Surface Modification: An Atomistic Simulation Study

Surface modification is an effective way to improve the dispersion of nanofillers in a polymer matrix and tune the interfacial interactions that determine macroscopic properties in polymer nanocomposites. In this work, we present a detailed investigation of silane modification effects on polymer interfacial conformation and dynamic properties through atomistic molecular dynamics simulations, using cis-1,4 polyisoprene (the major component of natural rubber) and amorphous silica substrate as a model system. Industrially relevant modified substrates are constructed with alkylsilane agents grafted at different surface densities. Contrasting systems with the modified substrates to the bare substrate case, we show that silane grafting effectively modulates chain conformations near the silica surface in terms of train, loop, and tail configurations, highlighting the separate effects of silane grafting density and agent chain length. We examine the variation of polymer dynamics in desorption, relaxation, and diffusion, which demonstrates the weakening of dynamic slowing down at the interface due to the silane presence and further exposes the dominant effects of surface train segments on the dynamic properties. Our results offer microscopic information on interfacial behavior while identifying key factors for tailoring interfacial dynamics. These findings provide useful insight into the reinforcement mechanism and serve as a first step toward the rational design of rubber composite materials via chemically detailed computational modeling.