The Use of Monochromated XPS to Evaluate Acid-Base Interactions at the PMMA/Oxidised Metal Interface

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Abstract
Recent studies have proposed that a near-interface conformation of PMMA in PMMA/metal substrate systems is different from the bulk polymer. High-resolution XPS analysis using monochromated X-ray sources has shown that PMMA interactions with metal oxide substrates are determined by the acido-basic nature of the substrate. It has also been shown that PMMA interacts with acidic sites on oxidised silicon via the carbonyl oxygen, and strongly basic sties on oxidised copper and nickel will react with the carboxyl carbon via nucleophilic attack. On amphoteric substrates, such as oxidised iron and aluminium, it is proposed that hydrolysis of the methyl ester occurs at weak basic sites to form a carboxylate, resulting in complexes being formed with the metal substrate. Such acid-base interactions would result in the orientation of PMMA at the interface to be dependent on the acido-basic nature of the substrate. This study also shows the resolution of a microfocussed monochromated X-ray source retrofitted to an older XPS spectrometer to be close to that of the Scienta ESCA 300 instrument.