UBC Theses and Dissertations
XPS studies of adhesion at organosilane/aluminum interfaces Leung, Yin-Ling
The work in this thesis deals with silane to aluminum adhesion. Angular dependent X-ray photoelectron spectroscopy (ADXPS) with the bias potential technique is used for the first time to probe silane/aluminum interfaces, the investigation aims to find evidence of direct chemical bonding between the two materials. 7074-T6 aluminum alloy panels are subjected to two surface pre treatments: degreasing treatment and chemical etching treatment which affect exposure of the Al oxide above the metal. Uppermost, though, is a carbon layer. ADXPS measurements show that the surfaces formed from these two treatments have different morphologies: one has continuous carbon and the other has carbon in patchy form. These different morphologies give different behavior in the adhesion. The organosilanes y-glycidoxypropyltrimethoxysilane (y-GPS), y-aminopropyltrimethoxysilane (Y-APS), and ymercaptopropyltrimethoxysilane (y-MGPS) were deposited on to the Al panels, and ADXPS was used to characterize the interfaces, as well as the orientations of the organofunctional groups. The combination of ADXPS and the new negative biasing potential technique, proposed by Pertsin and Pashunin, showed the presence of an extra peak in the Al2p spectra for y-GPS and y-MGPS deposited on to chemically etched aluminum. This extra structure may indicate that direct Al-O-Si bonding occurs between these silanes and the aluminum oxide. No significant change for the Al2p peak is found when y-GPS is deposited on degreased aluminum. That indicates that the continuous carbonaceous overlayer limits the interaction between the silane and the degreased aluminum, while the patchy carbonaceous overlayer provides some carbon-free aluminum oxide for interaction with the silane. By contrast, y-APS shows no evidence for direct chemical bonding with aluminum in either acidic medium (pH=3.0) or alkaline medium (pH=10.4). The structures of the y-APS films deduced from the ADXPS measurements explain this aspect: in both these cases the sSi-OH ends cannot approach the Al-OH groups on the metal surface, so no direct interaction takes place.
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