The Sheet-Contact Model

Equation 62 is very attractive for the study of adhesion between polymers and sohd surfaces, since it allows for the determination of the viscoelastic constants of the adhesive in the immediate vicinity of the contact. Unfortunately, the QCM does not work well with semi-infinite media when the viscosity, r], is larger than about 50 cP. The bandwidth in this case is too large. Most polymers exceed this limit. If, however, the contact area can be confined to a small spot in the center of the crystal the measurement becomes feasible [74]. Such a small contact area can, for instance, be estabhshed with a JKR tester [75]. The area of contact can be determined by optical microscopy. Of course, this kind of sample is laterally heterogeneous and the apphcabihty of simple models may be questioned. Experiment shows that the finite contact area can be reasonably well accounted for by modifying as  

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Interfacial viscoelastic spectroscopy on soft elastomers is possible by virtue of the sheet-contact model. 

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