Adsorption of PMMA on Oxidized Al and Si Substrates:  An Investigation by High-Resolution X-ray Photoelectron Spectroscopy

Abstract

The adsorption of medium molecular weight poly(methyl methacrylate) (PMMA) from an apolar solvent onto oxidized aluminum and silicon substrates has been studied by monochromated X-ray photoelectron spectroscopy (XPS). By recording the capacity of the solid surface for the polymer, by XPS, as a function of solution concentration, it has been possible to construct adsorption isotherms for the two systems under study. At low solution concentration, these isotherms are shown to conform to Langmuir adsorption and provide similar values of monolayer coverage, Γm, but significantly different values of the constant term, b, in the Langmuir equation were determined. At higher solution concentration, the adsorption isotherm was different due to an increase in Γm and a dramatic decrease in the constant b. Such observations are thought to result from a change in conformation of the adsorbed molecule at higher solution concentrations. Such effects are not associated with changes of conformation in solution but reflect the adsorption of a more compact molecule, which invariably forms fewer bonds with the substrate. The nature of the adsorption sites present in the oxidized metal substrates and their interactions with PMMA and conformation of the adsorbed molecules were interpreted from the high-resolution XPS spectra. These results were used to interpret the adsorption isotherms in terms of the acido-basic properties of the polymer and substrates, entropy of polymer solutions, and conformation of adsorbed molecules.

Corrosion Properties of UV Cured Hybrid Sol-Gel Coatings on AA7075-T6 Determined under Simulated Aircraft Conditions

“…3 Due to large in-depth analysis of EDS and its inability to detect organic layers this analysis cannot prove the possible formation of a thin carboxylate layer at the surrounding surface, as proposed. 43 As aluminum oxide can be considered as amphoteric in nature, the MAA probably interacts with 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.…”

Surface Modification of Polypropylene Molded Sheets by Means of Surface-Initiated ATRP of Methacrylates

“…The C 1s spectrum of PMMA-grafted sheet showed the four peaks at 285.0, 285.8, 286.9 and 289.1 eV corresponding to C 1 -C/C 1 -H, C 2 -COO, C 3 -OCO and C 4 =O, respectively. 25 The peak intensities assigned to the ester group (C 2 , C 3 and C 4 ) were significantly larger than that of PP-MI sheet. The O 1s spectra of PMMAgrafted sheet showed two peaks at 532.6 and 534.3 eV corresponding to O 1 =C and O 2 -CO, respectively (Figure 5b).…”

Organic–inorganic hybrid nanoparticles: adsorption characteristics of polyester resins

“…The ethyl ormosil however seems to show multilayer adsorption. Watts et al 3 , faced, apparently with the problem of multilayer adsorption (since one of the key assumptions of the Langmuir model is that it applies only to monolayer adsorption), determined that they were in fact observing a conformational effect due to increasing numbers of polymer-solvent interactions in high concentration solutions, leading to perturbation of the polymer chains which in turn allows a higher packing density when adsorbed onto a substrate. The alternative would be that the polymer chains were interacting in the higher concentration solutions.…”

“…The aim of the study is to derive adsorption isotherms from ToF-SIMS data. Adsorption isotherms have been established as a reliable method for determining certain aspects of the chemistry between a substrate and an adsorbate, such as the strength of their interaction [3][4][5][6] .…”