Contact Atomic Force Microscopy: A Powerful Tool in Adhesion Science

Abstract

Adhesion between two objects appears confusing or ambiguous, because the term is employed generally for two things: first, the formation of the interface between a pair of materials, i.e. the establishment of interfacial bonds through forces at the interface which cause materials to attract one another and second, the breaking stress or energy required to break the formed assembly. One can easily see that both interfacial forces and mechanical properties of adherents in the vicinity of the interface and in the bulk contribute to the global mechanical response of the assembly. Such a fundamental issue reflects a paradox that has stimulated intensive research for decades: what is the interplay between surface forces, surface rheology, and adhesive strength? In recent years, Atomic Force Microscopy (AFM) has become a powerful tool, sensitive enough, to detect small surface forces and to study adhesion at the nanoscale. Precise analysis of adhesion forces and surface mechanical properties of model polymer surfaces can be achieved with such a nanometer probe. The purpose and scope of this chapter is to highlight the experimental methods that enable one to dissociate the different contributions (chemical and mechanical) included in an AFM force-distance curve in order to establish quantitative relationships between interfacial tip–polymer interactions and surface viscoelastic properties of a polymer surface. New relationships are proposed that provide a complete understanding of how the adhesion separation energy depends on both surface chemistry and rheological behavior of the surface and thus at a local scale.