| Summary: | The interfacial effect is one of the significant factors in the glass-transition temperature (T<sub>g</sub>) of the polymeric thin film system, competing against the free surface effect. Herein, the T<sub>g</sub>s of poly (methyl methacrylate) (PMMA) films with different thicknesses and substrates are studied by fluorescence measurements, focusing on the influence of interfacial effects on the T<sub>g</sub>s. The strong interaction between PMMA and quartz substrate leads to increased T<sub>g</sub>s with the decreased thickness of the film. The plasmonic silver substrate causes enhanced fluorescence intensity near the interface, resulting in the delayed reduction of the T<sub>g</sub>s with the increasing film thickness. Moreover, as a proof of the interface-dependent T<sub>g</sub>s, hydrogen bonds of PMMA/quartz and molecules orientation of PMMA/silver are explored by the Raman spectroscopy, and the interfacial interaction energy is calculated by the molecular dynamics simulation. In this study, we probe the inter-relationship between the interfacial interactions arising from the different substrates and the T<sub>g</sub> behavior of polymer thin films.
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