| The prolific use of polymer/inorganic interfaces in emerging technologies necessitates a complete understanding of interface failure mechanisms, especially with respect to the effects of environment and interface chemistry. Motivated by an observed anomalous debonding phenomenon along the interface between a diglycidyl ether of bisphenol F (bisphenol F) epoxy polymer layer and a silicon nitride film, this work addresses debonding mechanisms and their relationship to interface chemistry, moisture diffusion, and mechanical fatigue. Weak interfacial bonding, suggested by low measured adhesion values, facilitates the stress-dependent transport mechanism that produces the anomalous behavior. A new model is developed to describe the effect of moisture diffusion through the polymer layer and ∼1 mum ahead of the debond tip where, upon sufficient accumulation of water molecules at the interface, weak interfacial hydrogen bonds are displaced, resulting in an insidious debond growth mechanism that occurs under both monotonic and cyclic loading. Moisture diffusion rates, and hence debond growth rates in this stress-dependent transport region, were moderated by blending organosilane molecules, namely amino, glycidoxy, and methacryloxy silanes, into the bisphenol F polymer layer. While only slight changes in layer mechanical properties and mechanical fatigue response were observed, significant effects on adhesion were observed to correlate with diffusion of blended organosilanes to the interface, which was driven by compatibility between organofunctional and epoxy moieties. By confining the organosilane molecules to the interface, a dramatic effect on adhesion and subcritical (amino) and discontinuous (glycidoxy, methacryloxy) silane layers stayed the stress-dependent transport mechanism, which was replaced by debond growth rate threshold behavior. Where the silane layer was discontinuous, debonding occurred along the bisphenol F/silicon nitride interface between silane islands and otherwise along the bisphenol F/silane interface, resulting in a characteristic stick-slip behavior that translated into negligible susceptibility of these systems to moisture attack under monotonic loading. Alternatively, where the silane layer was continuous the debonding mechanism is approached using a more traditional kinetic analysis. These effects, as well as the resultant threshold region mechanical fatigue behavior, have important implications for interface integrity approached from a defect tolerance perspective. |
