Applications of surface analysis techniques to studies of adhesion

Abstract

The question is often asked: “Which is the best surface chemistry tool for research on adhesive bonding?” This question is difficult to answer because it depends on the aspect of adhesion which is being studied. Often a combination of instruments must be used to take advantage of the strong points of each. In metal-to-metal bonding there are many facets of adhesive/adherend interaction. Elemental characterization of adherends, especially when composition with depth is desired, is often best accomplished with Auger electron spectroscopy (AES). When information of chemical bonding is required, X-ray photoelectron spectroscopy (XPS) is the choice of most workers. Extremely thin layers of material (when first layer surface sensitivity is needed) requires ion scattering spectrometry (ISS). The high sensitivity of secondary ion mass spectrometry (SIMS) to many elements important in adhesive bonding makes this technique useful, especially coupled with other methods, such as ISS and AES. Modern surface analysis along with scanning electron microscopy (SEM) provides information on failure surfaces to allow unequivocal determination of the mode of failure. Although original surfaces and failure surfaces following testing are relatively routinely analyzed, the characterization of the intact bond is not so easy. The interphase region between adherend and adhesive is smaller than the probe, exhibits charging and is unstable. Although no one technique adequately characterizes the bond interphase region, the SEM, the AES microprobe, and special techniques using transmission electron microscopy (TEM), may be used to gain some information about the bond. The more fundamental study of the interaction of polymers and polymer precursors with metal and alloys is carried out by surface energetics measurements, infrared and Raman spectroscopy, XPS and electron tunneling spectroscopy.