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 temperatures. For C? C bonding, values of the work G required per unit area to separate the sheets could be superposed to form a master curve versus peel rate using Williams-Landel-Ferry (WLF) temperature shift factors. Threshold values G_o at low rates and high temperatures ranged from virtually zero for nonbonded sheets up to the tear strength of the sheet itself, 50-80 J/m², for fully interlinked sheets, in proportion to the density of interfacial bonds. The strength thus appears to be the sum 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 μ′ upon oscillation frequency, an effective length of the fracture zone was deduced. It was extremely small in all cases, only about 1 Å. With sulfur interlinks, values of G were larger at all peel rates and varied more with temperature than predicted by the WLF relation. This is attributed to a concomitant decrease in S? S bond strength with temperature, and an increase in energy dissipation as the weaker sulfur bonds fail. © 1994 John Wiley & Sons, Inc.