Studies of metal-polymer interfaces
Creators: name: Kono, Mari
Publisher: name: University of British Columbia
Year: 2009

description: The chemistry of surfaces and interfaces formed by polymers and metals have been studied by surface science methods with the overall objective of gaining improved insights into interfacial adhesion. Three areas were emphasized: (i) interactions of thermally deposited metals with particular polymer surfaces; (ii) investigation of the possibility for using a remote hydrogen plasma for modifying polymer surfaces in controlled manners; and (iii) studies of the bonding of organosilanes to aluminum surfaces, in part with reference to developing nonchromating processes for corrosion protection. Interfaces formed between polyethyleneterephthalate (PET) and thin layers (&lt;10 Å) of thermally deposited aluminum or zirconium were characterized by X-ray photoelectron spectroscopy (XPS); it was concluded that the Zr bonds especially to O atoms in the PET surface, whereas the Al bonds both to carbonyl groups and to the aromatic rings. The conclusion for Al was suggested by new components in C ls at 283.9 eV and 282.6 eV, and by the O 1s component at 530.8 eV. Comparisons were also made with the Mg/PET interface, which shows Mg bonding as both O-Mg-C and metallic-like clusters. The deposition of Al on the Mg/PET sample results in some intermetallic mixing, which is manifested by alloy formation and Mg enrichment at the surface, but it also appears that some Al atoms penetrate the Mg region to react with carbonyl groups in the PET to form Al-C bonding. The stability of this sample was studied on exposing to air and to water. Although the metal overlayers are strongly modified by such treatments, it is suggested that the Al may help passivate the Mg/PET interface, for example in relation to light emitting diodes. The deposition of Al on polyphenylvinylene (PPV) showed Al-O-C and Al-C interactions at the interface, although appreciable oxidation occurs on heating to 80°C apparently via oxygen from the PPV bulk. The effects of the remote hydrogen plasma process were studied on the three polymers polystyrene (PS), poly(butylmethacrylate) (PBMA) and PET. The incorporation of new functional groups involving oxygen was established by curve fitting the XPS spectra, and these changes arise from small amounts of O-containing molecules (e.g. H₂0) in the background gas. After a standard treatment, the oxygenated components in C ls spectra correspond to 7.8%, 3.0% and 6.5% of the total C ls envelope area for PS, PBMA and PET respectively, and this indicates that the extent of modification depends on the specific polymer structure. Surfaces of high-purity aluminum, which have been given different pre-treatments and subsequent exposures to air and water, were shown to differ markedly with regard to chemical composition (e.g. the oxide film thicknesses range from 29 Å to 88 Å, while the fractions of oxygen in OH form vary from 0.2 to 0.9) and topographical structure (e.g. the mean roughness value ranges from 37 nm to 77 nm). Characterizations of these surfaces after exposures to three organosilanes, γ-glycidoxyl propyltrimethoxyl silane (γ-GPS), Bis-1,2- (triethoxysilyl)ethane (BTSE) and γ-aminopropyl trimethoxyl silane (γ-APS), indicate that the amount of silane adsorbed in each case shows a tendency to increase both with the number of OH groups detected at the oxidized aluminum surface and with the surface roughness. The XPS data are consistent with the adhesion of γ-APS occurring by H-bonding through NH₃⁺ groups.