From Chain Dynamics to Adhesion: Molecular Mechanisms of Polymer Interfaces

The performance of polymer-based materials is strongly influenced by molecular processes occurring at solid interfaces. Although polymer adsorption is widely recognized as a key factor, how interfacial chain dynamics determine macroscopic adhesion remains poorly understood. In this lecture, we present a molecular-level picture of polymer adhesion developed through advanced scanning probe microscopy and interfacial mechanical analyses. First, time-resolved atomic force microscopy was employed to visualize segmental relaxation dynamics of isolated polymer chains adsorbed on atomically flat substrates. The measurements revealed pronounced spatial heterogeneity in chain mobility arising from transient adsorption events. Moreover, the influence of adsorption extended beyond directly contacted segments through dynamic coupling with neighboring chains. Next, long-time polymer mobility near solid interfaces was investigated using nano-creep measurements. The results revealed a hierarchical dynamic structure consisting of a strongly constrained adsorbed layer and an overlying region with suppressed mobility, demonstrating that interfacial constraints propagate far beyond the adsorbed layer. Finally, the relationship between interfacial structure and adhesion strength was examined using the Surface and Interfacial Cutting Analysis System. The results showed that adhesion strength increased with the development of the adsorbed layer and was governed primarily by the total interaction energy generated by chain segments in contact with the substrate. These findings establish a unified framework linking chain adsorption, interfacial dynamics, and adhesion. They demonstrate that polymer adhesion is governed not only by static interfacial structures but also by dynamic coupling processes spanning multiple length and time scales. The results provide molecular design principles for high-performance adhesives and advanced polymer-based materials.