Invited Paper AS-MoA1
Probing the Interfacial Chemistry of Polymer-Metal Systems with Electron Spectroscopy

Monday, October 20, 2008, 2:00 pm, Room 207

The nature of the interface between a polymer phase and a metallic substrate is crucial in many important technological endeavours, for example; adhesive bonding, organic coatings for corrosion protection and sealants. XPS has been used for many years for the forensic analysis of failed interfaces, and in some cases the analysis of interfacial failure surfaces may provide a means to understanding adhesion, and perhaps even identifying certain species that are responsible for compromising performance. However in most cases it is necessary to resort to specimen preparation strategies that allow the surface chemical analysis of the necessarily thin layer responsible for adhesion between the two phases in order to investigate the interfacial chemistry of adhesion. Two methods developed in the author’s laboratory, which allow access to the interfacial region, will be described. The deposition of a very thin layer (< 2nm) of organic material, either a component of an adhesive or coating or a dilute solution of the fully formulated system itself, provides a route to probing the interfacial chemistry directly using XPS and ToF-SIMS. The C1s XPS data provides information regarding the changes in carbon chemistry occurring at the interface and fine structure in cationic spectra provide indications of bond formation between organic layer and substrate. This may lead to the conclusion of the existence of specific interactions across the interface and the presence of these can often be confirmed with ToF-SIMS. An alternative approach is to section a polymer/metal system to expose the interface for analysis. The use of ultra-low angle microtomy (ULAM) cut at angle in the range of 0.003 – 2 degrees relative to the interface has been shown to be extremely effective. Once prepared small area XPS can bee used to profile across the interface and in the best cases a depth resolution of < 20 nm can be achieved. Using this approach it has been possible to establish the interdiffusion of active components in a paint system and the aggregation of adhesion promoter molecules, incorporated in an adhesive formulation, at the interface of aluminium bonded with a commercial epoxy adhesive.