In Situ Characterization of the Initial Effect of Water on Molecular Interactions at the Interface of Organic/Inorganic Hybrid Systems

Probing initial interactions at the interface of hybrid systems under humid conditions has the potential to reveal the local chemical environment at solid/solid interfaces under real-world, technologically relevant conditions. Analyzing this region and characterizing the influence of atmospheric circumstances (such as water ingress) is challenging. Common surface sensitive analysis techniques only operate under vacuum conditions, making it impossible to probe environmental effects in-situ. Here, we show for the first time that ambient pressure X-ray photoelectron spectroscopy (APXPS) with a conventional X-ray source can be used to study the effects of water exposure on the interaction of nanometer-thin polyacrylic acid (PAA) and polymethyl methacrylate (PMMA) layers with a native aluminum oxide surface. The formation of a carboxylate ionic bond at the interface is characterized.1-3 When water is dosed in the APXPS chamber up to 5 Torr (~28 % relative humidity), an increase in the amount of ionic bonds at the interface of the PAA thin films is observed. To confirm our APXPS interpretation, complementary in-situ ATR-FTIR Kretschmann experiments on a similar model system are conducted.4 This vibrational spectroscopy technique using the so-called Kretschmann configuration is used to characterize the formed bonds at the metal oxide/polymer interface. An Al layer is sputtered on an IR transparent crystal, with the Al thickness selected such that the FTIR signal from the oxide/polymer interface is amplified as a result of the Kretschmann effect, and thus an interface-specific spectrum of the oxide/polymer surface is attained. This way, we have direct access to the interface, and the influence of an above-the-polymer electrolyte (i.e. H2O) can be probed. These spectra also demonstrate that water first leads to an increased wet adhesion through increased ionic bond formation.