Atomic force microscopy allows observation of the adhesive surface and characterization of the adhesive behavior on a nanoscale level, providing new and important information about the behavior of pressure-sensitive adhesives (PSAs). In this research PSAs consisting of poly(ethylene propylene) and the n-butyl ester of abietic acid are studied. Results of nanoindentation measurements indicate two different types of behavior:  a viscoelastic behavior in the tackifier-rich domains and a more highly dissipative response in the matrix with a gradual transition behavior in areas close to the interfaces between the domains and the matrix. The adhesive energy appears to be dictated predominantly by the tackifier-rich domains.

Microindentation and nanoindentation measurements of model pressure-sensitive adhesives have been used along with scanning probe imaging to follow changes in properties with aging. One blend that is initially miscible stiffens markedly with time for tackifier loadings above a certain value. Lateral phase segregation at the surface is seen for some of the blends along with strong increases in stiffness. Changes with time are less pronounced in the miscible blend with a tackifier stabilized by hydrogenation. While microindentation provides quantitative measurement of changes in overall stiffness and adhesive performance, nanoindentation provides lateral resolution of the changes near the surface. Of the techniques used here, phase detection mode scanning probe imaging provides the most highly surface selective means of noting changes in properties with aging.

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