Observation of the Interfacial Layer Designed to Improve Polymer Adhesion

Polymer adhesion with inorganic materials is a crucial technology for realizing the diversification of materials. When a polymer contacts with inorganic materials, a layer containing strongly- and loosely-adsorbed chains is formed at the surface. The former and latter are chains that mainly adopt train and loop/tail conformations, respectively. To improve the interfacial adhesion, controlling the interaction between loosely-adsorbed chains and bulk-free chains is essential. We here succeeded in improving the interfacial strength by chemically cross-linking them. Polymer chains were attached to the surface of a silicon (Si) wafer and then a film of isotactic polypropylene or polyamide 6 was mounted on it to produce our model system. As loosely-adsorbed chains have photo-cross-linkable moieties, the adherend film could be strongly adhered to the Si wafer via the adsorbed layer. Real-space observation helped us prove the aggregation states of chains at the interface. Atomic force microscopic observation confirmed the well-defined structure, in which chains adsorbed by the first and second processes were strongly- and loosely- attached to the Si wafer. X-ray photoelectron spectroscopic imaging of the adhesive interface obtained by the obliquely cut sample revealed that the bulk chains were chemically bound to the adsorbed layer.