Cavity nucleation and delamination during adhesive transfer of a thin viscoelastic film

A model acrylic copolymer system was used to study the processes involved in the transfer of a thin viscoelastic film from a weakly adhesive elastomeric substrate to a more strongly adhesive surface. The film consisted of a layer of acrylic diblock copolymer micelles that was spun cast onto a silicone elastomer from a suspension in butanol. A circular portion of the layer was transferred to a hemispherical glass indenter with which it was brought into contact. The transfer of the film during tensile loading of the indenter began with nucleation of a cavity at the film/elastomer interface and was followed by delamination of the film at this interface. Statistical variations in cavity nucleation for identical loading conditions were quantified by defining a Weibull modulus similar to that used to describe the failure of brittle materials. The average energy release rate required for cavity nucleation at a fixed induction time increased with film thickness in a way that is consistent with the existence of a critical value of the hydrostatic tension at the film/substrate interface. This critical hydrostatic tension was comparable in magnitude to the elastic modulus of the substrate and was about ten times the elastic modulus of the thin film.