Atomic force microscopy (AFM) and X-ray reflectivity (XR) have been used together to provide a detailed and direct look at the structure of human serum albumin protein adsorbed onto well-characterized selfassembled monolayer (SAM) surfaces at several protein concentrations. The duration of SAM deposition was also varied to investigate the influence of the density of hydrocarbon chains in the SAM on protein binding tenacity. Concurrent study of adsorption to bare silicon wafers with native oxide surfaces provided a comparison with a hydrophilic surface similar to widely studied glass and quartz surfaces. Both AFM and XR measurements showed that after adsorption, rinsing, and drying, the surfaces of all substrates were covered with no more than a single layer of adsorbed protein. Thin dense protein layers were seen for the substrates exposed to protein concentrations of 0.1 and 0.5 mg/mL. Partial surface coverage by protein aggregates having larger thicknesses was seen for substrates exposed to lower concentrations. The tenacity of the protein adsorption on different substrates was tested by eluting the adsorbed protein with a 1% solution of sodium dodecyl sulfate surfactant. This treatment removed almost all protein from the bare silicon surface and from the fully formed, dense SAMs. A significant amount of adsorbed protein remained on the surface of the less dense, "incomplete" monolayers, suggesting that protein adsorbed more tenaciously on that surface.

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.

No abstract

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.

No abstract