Microprobing of interfacial behavior of solid polymers by means of normal mechanical contacts Y. S. Garif, W. W. Gerberich, C. W. Macosko and A. Pocius 1 Dept. of Chemical Engineering and Materials Science, University of Minnesota Minneapolis, MN 55455 U.S.A. 1 3M Company, Adhesive Technologies Center St. Paul, MN 55144 U.S.A. ABSTRACT Adhesion properties of acrylic pressure sensitive adhesives were examined by means of normal (JKR) contact at room temperature. Cylindrically shaped samples were synthesized in capillary tubes in presence of a cross-linking agent in order to obtain an elastic response. The results reveal power law increase of adhesion at higher rates of interfacial separation. Transition from low- to high-power is revealed and explained as a result of bulk shielding of interfacial fracture mechanism. Further results will be available soon. Bulk viscoelastic dissipation and molecular interactions at the interface are thought to jointly govern this behavior. INTRODUCTION The adhesion energy of interfaces between dissimilar polymer materials exerts a critical influence on numerous problems of technological importance 1,2 , particularly the adhesive bond strength of pressure-sensitive adhesives 3 . In order to characterize interfacial fracture in these types of systems, a practicable contact mechanics formulation (JKR) 4 was used to interpret raw data. The technique monitors evolution of a normal contact 5 between soft polymer samples during slow loading and unloading. Analysis of experimental measurements and observations focuses on rate- dependence of polymer adhesion 6 . The goal is to expand conceptual understanding 7,8 of the adhesion behavior of polymers by examining the interplay of viscoelastic effects in the bulk and chain rearrangement at the interface. THEORY AND EXPERIMENT The adhesion test used in this study utilizes normal contact between two polymer cylinders of a known diameter. Crossed at 90 o , they are slowly pressed against each other and then separated at a specified rate. The test monitors dynamics of interfacial formation and separation 9,10 by recording both load and area of contact during loading/unloading. In order to analyze the raw data, the JKR theory 11 was used as a better fit for soft contacts than other contact mechanical theories 12,13,14 . DD7.5.1 Mat. Res. Soc. Symp. Proc. Vol. 710 © 2002 Materials Research Society