Polymer-polymer adhesion energy dependence on interfacial crack propagation rates has been investigated in a number of various systems, by means of sliding and normal contacts. It was found that interfacial behavior is sensitive to crack propagation rate. At most rates, the extent of such sensitivity is dominated by visco-elastic properties of the bulk around the interface (also observed with conventional adhesion tests such as peel, wedge, blister, etc.). However, below a certain critical crack propagation rate (on the order of 1 micron/sec), interfacial behavior suddenly becomes much less rate-dependent. In both regimes, above or below the critical rate, measured adhesion energies can be fit with a power law where power, or rate sensitivity, is less than 0.5. These findings are a result of an extensive adhesion testing carried out with the following two independent contact mechanics- based techniques: (1) cross-sectional scratch (CSS) employs sliding contact of an indenter across a stack of polymer layers to induce fracture of stiff interfaces. (2) JKR-test utilized normal contact between two cylindrically shaped samples of interest to monitor slow formation and fracture of soft polymer interfaces. Finally, a preliminary attempt to correlate adhesion behavior observed with both techniques was made. JKR test measures adhesion in a range of low crack propagation rates of 1 nm/s to a few μm/s. The CSS adhesion data lie in the range of approximately 1 μm/s to a few mm/s. Low-rate (sub-critical) JKR adhesion results reflect intrinsic interfacial energy. Both CSS and high-rate JKR adhesion results reflect comparatively well visco-elastic properties of bulk around the interface. Most other conventional adhesion tests measure adhesion energy at higher rates and on a different scale. However, based on findings of this study, it is expected that a power law fit of adhesion data for a given system should have the same power law index independent of the test used.
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