Interfacial Confinement of Thermal Motion in Adsorbed Polystyrene Chains

Polymer chains adsorbed on solid surfaces are known to adopt local conformations called loops and trains, which correspond to segments that are non-contacting and contacting the surface, respectively. Thus, direct observation of the thermal motion of such segments is expected to advance the fundamental understanding of molecular motion associated with interfacial formation and adsorption. In this study, we visualized the thermal motion of isolated polystyrene chains with a number-average molecular weight of approximately 2M adsorbed on a silicon substrate using atomic force microscopy (AFM) under a nitrogen atmosphere at various temperatures. The obtained height images revealed string-like structures with globular portions at both ends, in good agreement with the results of molecular dynamics simulations. Time-resolved AFM observations showed height fluctuations along the chains, demonstrating the coexistence of loop and train conformations. Furthermore, two-dimensional mapping of the relaxation time revealed heterogeneity in the molecular motion along the chains.