Adhesives SIMS data

As can be seen, some larger fragments are seen in the sample held at elevated temperature, and sodium has segregated to the surface. Such segregation is very common in high temperature cured specimens, where sodium is often found at the failure surface in an adhesive failure mode. ISS/SIMS data from the adhesive side of a titanium-epoxy failure interface from a tensile test specimen are shown, in Figure 8. 

Figure 8. ISS/SIMS Data From Tape Epoxy Adhesive Debonded From Titanium...

Figure 10. 1SS/SIMS data from adhesive matching areas to adherend shown in...

Fig. 46 Data obtained on PS/PSox patterned surfaces produced by photolithography and oxygen plasma oxidation of polystyrene (a) XPS mapping of the O Is peak intensity (obtained with a Kratos Axis Ultra spectrometer) (b) adhesion map obtained by AFM in water with a sUicon probe (vertical scale = 25 nN), revealing the hydrophobicity contrast in the pattern (c) ToF-SIMS image recorded with the signal of CNO ions on a patterned surface conditioned with a solution of flbronectin and Plutonic F68, revealing the selective adsorption of the extracellular matrix protein on the oxidized tracks and (d) micrograph of rat hepatocytes on a patterned substrate conditioned with a solution of type I collagen and Plutonic F68, showing the selective adhesion of the cells on the oxidized tracks. Adapted from Refs, 25 and 312...

SAM is a technique that can sample extremely small volumes of material (probably the smallest of any technique without the need for extensive sample preparation) and for this reason the choice of sample and the manner in which the analysis is carried out is extremely important. As with any electron microscopy-based analysis method, the need to acquire data from a representative sample of the specimen must be uppermost in the mind of the analyst. As SAM is an electron beam technique it is really only applicable to conductors or semiconductors, a useful guide being that if the specimen can be imaged in an SEM without sample charging SAM will be possible. For these reasons the role of AES/SAM in adhesion studies is restricted to the analysis of metallic substrates and pretreatment layers. There are ways in which it is possible to apply the technique to insulators (Baer et al. 2010) but analysis of polymers by AES is not practicable the usual approach being to use XPS or ToF-SIMS. 

This example relies on the identification of an element at the failure interface that can be used as a marker for a particular component in the formulation. More usual is the need to resort to high resolution spectroscopy. The data of O Fig. 10.8 relates to a radiation-cured adhesive being developed for the bonding of components to ceramic substrates for surface mount technology. Once again water reduced the adhesion below an acceptable level and XPS and ToF-SIMS analysis of the failure surfaces provides an indication of the cause of the failure. The adhesive has two major components an aromatic adhesive part and an aliphatic reactive diluent. Inspection of the high resolution Cls spectra from the adhesive side of the failure shows the expected Jt —> Jt shake-up satellite diagnostic of the aromatic component of the adhesive (Watts and Taylor 1995). The ceramic failure surface shows a small amount of carbon... 

In the case of the GPS organosilane adhesion promoter applied to aluminum (and used as a substrate in the data of Fig. 10.13), ToF-SIMS has established the formation of a covalent bond between the GPS molecule and the oxidized aluminum substrate (Abel et al. 2000). The chemistry leading to the formation of the diagnostic fragment (Al-O-Si at m/z = 70.9534 u) and the high resolution spectrum at a nominal mass of 71 u is shown in Fig. 10.15. The formation of the specific bond is associated with good durability of the resultant bond, and examination of the fracture surfaces of failed joints shows that the presence of the ion in the ToF-SIMS spectrum correlates well with good durability. 

The use of XPS and ToF-SIMS has much to recommend for the investigation of the interfacial chemistry of adhesion. In the most advantageous cases the analysis of fracture surfaces has the potential to provide such information but one must ensure that failure has occurred within the interphase this will not always be the case and the onus, as always, is on the researcher rather than the analyst, to interpret the analytical data correctly in the context in which the analysis was made. If fracture surfaces do not provide access to the interphase it is necessary to resort to sectioning of the system to expose, possibly with sputter depth profiling, the interphase region itself for analysis. An alternative method is to use dilute solutions, based on either individual components of a formulation, or the complete adhesive or coating itself This allows the determination of adsorption isotherms that measure the capacity of a solid surface for... 

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