Interfacial interactions of plasma-polymerized acrylic acid and an oxidized aluminium surface investigated using XPS, FTIR and poly(acrylic acid) as a model compound

X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) are used to characterize the interface between poly(acrylic acid) (PAA) and an aluminium oxyhydroxide (AlOOH) surface. Reaction of the PAA carboxylic acid functionality with hydroxyl groups at the surface of the oxide to form a monodentate carboxylate complex C(O)OAl was identified by FTIR. The degree of conversion of the acid to the salt at the interface was estimated to be 40% from the XPS analysis of PAA overlayers of varying thickness. An equivalent reaction was identified at the interface between AlOOH and a monolayer of strongly bonded plasma-polymerized acrylic acid (ppAAc) that remained after solvent washing. The resistance of the monolayer of ppAAc to solvent washing was attributed to the formation of interfacial carboxylate complexes with the AlOOH surface.