Chain Fluidity of Polystyrene near Solid Substrate

Understanding chain dynamics near solid interfaces is crucial for designing high-performance polymer nanocomposites and adhesive technologies. Previous studies have revealed that the orientational relaxation of functional groups as well as the segmental motion are more restricted at the interfaces than in the bulk. Thus, it is reasonable to assume that the motion of entire chains near solid interfaces are also restricted, and the extent of this restriction influences the deformation and long-term performance of materials. However, such a larger spatial- and longer time-scale motion of polymer chains near solid interfaces remains unclear. In this study, nano-creep tests for polystyrene (PS) thin films on silicon (Si) substrates were conducted to investigate the chain fluidity near the solid interfaces. As a result, PS chains at the outermost interface did not flow even at a temperature 45 K higher than the glass transition temperature in the bulk. Additionally, at the top of the outermost layer, there were chains that could flow, but their fluidity was reduced compared to that in the bulk. This could be understood by assuming that the tube dilation of interfacial chains was suppressed due to the presence of adsorbed chains and the solid interface.