Effect of the Molecular-Scale Surface Characteristics of Carbon Black and Silica on Interfacial Interactions

Carbon black (CB) and silica are the most widely used reinforcing fillers for rubber composites. However, their molecular-scale surface differences and quantitative effects on interfacial interactions remain unclear, hindering the rational design of high-performance materials. In this study, CB- and silica-filled composites with equivalent interfacial areas were prepared to experimentally compare their interfacial interaction strengths. Molecular dynamics simulations using <i>trans</i>-3-hexene as probe molecules subsequently quantified the interaction strengths of CB and silica, showing good agreement with the experiments. Further analyses of surface energy distribution and the dependence of binding energy on adsorption distance revealed that the molecular-scale surface characteristics differ in three key aspects: adsorption energy, energy heterogeneity, and binding energy-distance correlation, thereby accounting for the inferior performance of silica-NR interfaces despite the presence of covalent bonding. On the basis of the simulation results, experiments under equivalent interfacial adsorption energies confirmed that interfacial physical adsorption dominates the overall interfacial interactions and validated the critical role of specific strong binding sites. In this study, an efficient molecular simulation methodology was established to overcome experimental limitations, and by integrating simulations with experiments, the influence of filler surface characteristics on interfacial interactions was elucidated, providing guidance for rational composite design.