Adhesion Depends on Interfacial Strength: Time and Temperature Effects

In the conventional description, peeling of an adhesive from a solid substrate is expressed in terms of adhesion energies at adhesive-substrate interfaces. However, this energy-based perspective faced considerable difficulties in explaining why the adhesion energy, also known as peel strength Γ_p, is many orders of magnitude greater than Dupré's thermodynamic work of adhesion, Γ₀. In this study, we present experimental evidence to demonstrate that polymer adhesion is governed by interfacial strength σ_interf, defined by the pair of adhesive and substrate. A tensile adhesion test is performed to estimate σ_interf from adhesion strength σ_adh equal to the engineering stress at detachment. This test stretches, at various rates under different temperatures, one end of a ribbon-like specimen with the other end adhered to the same substrate used in peeling tests until adhesive detachment. The dependence of σ_adh on applied rate and temperature is found to be the same as that of Γ_p from conventional peeling tests on peeling speed v_p and temperature. Our stress perspective shows that Γ_p explicitly correlates with σ_adh through a characteristic length scale P instead of Γ₀. Here, P is the distance from the peeling front, beyond which the adhesive undergoes little deformation. Since P is a much larger length scale than a molecular scale and σ_adh directly depends on polymer-substrate interfacial interactions, Γ_p explicitly depends on σ_interf. As activated processes, in both peeling and tensile adhesion tests, interfacial debonding on shorter time scales and lower temperature required higher interfacial stress.