K. L. Ngai, Daniele Prevosto and Luigi Grassia
The anomalous viscoelastic creep behavior of ultrathin polymer films fabricated by nanobubble inflation is explained by the Coupling Model. Present in the glass-rubber transition region are the segmental α-relaxation, the sub-Rouse modes, and the Rouse modes. On decreasing film thickness, the α-relaxation is shifted to shorter times, due to reduction of intermolecular coupling, and to a lesser degree for the sub-Rouse modes, whereas the Rouse modes remain unchanged or becomes even slower. These differences cause the viscoelastic anomalies found in the nanobubble thin-film creep experiments.