Linear viscoelasticity and non-linear elasticity of block copolymer blends used as soft adhesives

The debonding of pressure-sensitive-adhesives from a rigid surface often occurs with the formation of a fibrillar structure bridging the surface and the adhesive. This fibrillar structure is responsible for the large (of the order of 1 kJ/m(2)) adhesion energy, which is measured, for this type of adhesive despite the very low level of applied stress. One way to account for this dissipated energy is viscous flow in the elongation process of the fibrils. However, for certain types of adhesives, the extension of the fibrils is essentially a quasi reversible elastic process and the energy is only dissipated rather rapidly when the fibrils are detached from the surface. It is therefore essential to characterize the elastic properties of theses adhesives not only in the linear viscoelastic regime but also in the large strain non-linear elastic domain. We have therefore performed tensile tests of model adhesive films based on block copolymers. The respective roles played by the linear viscoelasticity and non-linear elasticity in controlling the properties will be discussed.