Effect of interfacial local conformation of polymer chains on adhesion strength†

The aggregation states of polymer chains at solid interfaces are strongly related to their adhesion properties. In this study, we focused on sum-frequency generation (SFG) vibrational spectroscopy, which offers the best depth resolution at the sub-nanometer level among available techniques, and explored its potential as an imaging method. A poly(methyl methacrylate) (PMMA) thin film with a line-and-space pattern was prepared on a quartz substrate. Imaging of the interfacial line-and-space structure in the film was successfully achieved based on SFG signals arising from ester methyl groups as well as carbonyl groups. Once SFG imaging was established, it was applied to blend films of polystyrene (PS) and PMMA with different compositions on the quartz substrate, enabling the direct and non-destructive observation of wetting layers and phase-separated structures buried at the substrate interface for the first time. The interfacial adhesion strength between the blend films and the quartz substrate, evaluated using the surface and interfacial cutting analysis system, showed a clear correlation with the interfacial structure of the blend. This study, which enables the analysis of the relationship between the local orientation of polymer chains at the interface and adhesion strength, is expected to contribute greatly to the design of next-generation adhesives and adhesion technologies.