XPS investigations of acid-base interactions in adhesion. Part 3. Evidence for orientation of carbonyl groups from poly(methylmethacrylate) (PMMA) at the PMMA-glass and PMMA-SiO 2 interfaces

Abstract

The effect of the substrate acidity/basicity on the orientation of the carbonyl group (CO) from poly(methylmethacrylate) (PMMA) has been investigated by X-ray photoelectron spectroscopy (XPS). Analyses of the underside of PMMA films cast onto glass microscope slides, and silicon dioxide thermally grown on a silicon wafer, indicated an increasing intensity ratio O1s(CO)/O1s(OCH 3) with the substrate acidity. The XPS measure of substrate acidity was monitored by an O1s + Si2p binding energy parameter (∑BE) or an O1s - Si2p binding energy (ΔBE). Both ∑BE and ΔBE increase with the acidity of the pretreatment solutions (low pH). The PMMA XPS results suggest a preferential orientation of the carbonyl group at the interface when PMMA is solvent cast onto the substrate, a phenomenon which is most pronounced for the very acidic substrate. This orientation is most probably related to an interfacial acid-base interaction between the surface acidic sites of the substrate and the oxygen of the basic carbonyl group from PMMA.