Adhesion of heterogeneous thin films—I: Elastic heterogeneity

We study the adhesion of thin films on rigid substrates in the presence of spatial heterogeneities. While adhesion is relatively well-understood in the context of homogeneous systems, much remains open concerning the adhesion of heterogeneous systems. In this paper, we focus on thin adhesive tape with heterogeneities in the elastic stiffness, and show that these heterogeneities have a profound effect on adhesion raising the effective force required to peel the film by an order of magnitude with no modification of the actual adhesive interface. We show through theory and experiment that this apparent increase is caused by fluctuations in the elastic bending energy. We also show that heterogeneities can be used to create asymmetry in that the force required to peel the tape in one direction can be different from that in the other. In short, this work shows that fluctuations in a small component of the overall energy of the system can give rise to a significant macroscopic consequence. We comment on the broader implications of this observation.