Aging of model pressure sensitive adhesives studied with scanning probe microscopy

Changes in the surface morphology and surface friction of a tackified model pressure sensitive adhesive (PSA) with aging have been observed directly with atomic force microscopy. Changes over many months at room temperature as well as changes during brief exposure to two elevated temperatures (65 and 100 degreesC) were characterized. Performance of the PSA, consisting of poly(ethylene propylene) with n-butyl ester of abietic acid as the tackifier, was studied qualitatively with nanoindentation. Tackifier-enriched domains at the blends' surfaces grew and then coalesced with aging and the surface friction decreased as a result. Also, the polymer-enriched matrix stiffened with time. These two effects led to a stiffer surface, poorly suited to wetting an adherend. Domain coalescence was markedly accelerated upon brief exposure to a temperature ramp up to 100 degreesC. At the highest temperatures studied, degradation of the polymeric matrix decreased its stiffness.