From Single-Chain Adsorption to Aggregate-Scale Adhesion: AFM Insights into Polyisoprene–Inorganic Interfacial Interactions

Abstract Understanding the interactions between polymers and inorganic fillers is crucial for enhancing interfacial effects and optimizing the mechanical properties of polymer nanocomposites. We used two atomic force microscopy (AFM)-based nanomechanical techniques: nanomechanical AFM mapping and single-molecule force spectroscopy (SMFS), to quantitatively characterize the adhesion between polymers and inorganic materials from the aggregate scale to the single-chain scale. This study reveals the relationship between single-molecule interactions and adhesion behavior at the aggregate scale by comparing the interactions between cis-1,4-polyisoprene (PI) monolayers and inorganic substrates with the adhesion between inorganic-coated probes and cross-linked isoprene rubber (IR). In addition, SMFS measurements reveal solvent-dependent adsorption conformations and substrate-dependent desorption forces, enabling quantitative analysis of adsorption at the molecular scale. For PI, which lacks strongly interacting polar functional groups, nonspecific van der Waals-dominated interactions are expected to contribute substantially to its interactions with the inorganic substrates. The observed substrate dependence reflects differences in interfacial characteristics, including surface free energy. Furthermore, by measuring the adhesion energy at the PI aggregate scale via nanomechanical AFM mapping using surface-modified probes, the results revealed a trend similar to that observed in a single polymer chain. This cross-scale consistency highlights substrate surface characteristics as important factors regulating polymer–inorganic interfacial interactions. This research methodology provides an effective strategy for rational design of interface interactions and lays a theoretical foundation for structural optimization and performance enhancement of high-performance polymer composites.