Interfacial adsorption competing with thermal mixing in confined hydrogen-bonded polymer bilayers

neutron reflectivity, and near-edge X-ray absorption fine structure spectroscopy. Thermal annealing induced progressive interdiffusion and eventual miscibility across the bilayer. However, even after apparent homogenization, a nanometer-thick PVPh-rich layer persisted at the substrate interface and remained resistant to dissolution in a good solvent. Neutron scattering length density profiles revealed that this low-SLD interfacial region survived at elevated temperatures, while surface-sensitive spectroscopy confirmed preferential enrichment and strongly stabilized adsorption of PVPh chains at the oxide interface. These findings demonstrate that strong polymer-substrate interactions can arrest complete interfacial homogenization under confinement, generating asymmetric composition profiles despite bulk miscibility. The results highlight the fundamental role of surface-induced stabilization of adsorbed chains in governing mixing and structural evolution in ultrathin polymer films.