INTERFACIAL BONDING, ENERGY-DISSIPATION, AND ADHESION

Thin sheets of several elastomers have been adhered together by C-C or S-S interfacial bonds and peeled apart at various rates and temperatu res. For C-C bonding, values of the work G required per unit area to s eparate the sheets could be superposed to form a master curve versus p eel rate using Williams-Landel-Ferry (WLF) temperature shift factors. Threshold values G(o) at low rates and high temperatures ranged from v irtually zero for nonbonded sheets up to the tear strength of the shee t itself, 50-80 J/m2, for fully interlinked sheets, in proportion to t he density of interfacial bonds. The strength thus appears to be the s um of two terms: G(o) and a viscoelastic loss function which itself is approximately proportional to G(o). By comparing the dependence of G upon rate of peel with the dependence of dynamic shear modulus mu' upo n oscillation frequency, an effective length of the fracture zone was deduced. It was extremely small in all cases, only about 1 angstrom. W ith sulfur interlinks, values of G were larger at all peel rates and v aried more with temperature than predicted by the WLF relation. This i s attributed to a concomitant decrease in S-S bond strength with tempe rature, and an increase in energy dissipation as the weaker sulfur bon ds fail. (C) 1994 John Wiley & Sons, Inc.