Abstract
The nature of the surface to be bonded can have a profound effect on both the initial strength and the performance of an adhesive joint. This chapter reviews methods that can provide microscopic, physical, and chemical information relating to surface characteristics. Three forms of microscopy are described, together with stylus profilometry, which enables surface roughness to be quantified. The thermodynamics of surfaces are conveniently considered by wetting and spreading tests which can range from very simple (water break test and Dyne inks) through to the observation and evaluation of sessile drops on surfaces using the well-known Young equation. Surface chemical analysis is rather more specialised, but X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry have been widely utilised in adhesion studies and a number of examples are provided to illustrate their worth. It is often convenient to combine these two methods with insert gas sputtering to produce compositional depth profiles, and such approaches are briefly introduced. The failure of an adhesive joint will yield two failure surfaces, and careful examination of these allows the locus of failure to be defined. Guidelines are provided to allow the purposeful choice of the characterisation method when undertaking studies of this nature.