Mesoscopic Fibrillation Properties of Pressure Sensitive\nAdhesives Based on Latex Films

Abstract

Slow pulling experiments with atomic force microscope (AFM) tips were performed on industrial acrylic\nlatices, where the Brownian motion of the tip was monitored in parallel to the static force. From the noise\npower spectra of the tip's thermal motion, one can infer the effective spring constant and the drag coefficient\nof the tip−sample system. The results from AFM pulling experiments correlate well with macroscopic tack\ntests performed on the same materials at comparable stress levels. The fraction of “successful pulls”,\nmeaning pulls where an extended loop of adhesion hysteresis forms, decreases with aging. Presumably,\nthe internal cohesion of the material increases as film formation proceeds, such that the formation of cusps\nor tip-induced deformations of the surface becomes less likely. For the most tacky material, the formation\nof a continuous film was incomplete even after 6 months of storage. The successful pulls are characterized\nby a discrete number of steps in both static force and the spring constant. The steps are attributed to the\nrupture events occurring inside the film. Internal heterogeneity has an influence on the tack.