Pull an adhesive tape slowly off a surface and you’ll see it: tiny voids form in the adhesive layer, stretch into fibrils, and eventually snap. The standard explanation treats cavitation as an elastic instability — the material is incompressible, so expansion in one direction must be accommodated by contraction elsewhere, and beyond some critical stretch the math predicts a cavity must nucleate.

But there’s a problem with the elastic story. It requires a pre-existing defect — a seed void, an inhomogeneity, something to nucleate around. Real adhesives cavitate in pristine material. The cavity appears from nothing.

The alternative: treat the elastomer not as an elastic solid but as a crosslinked van der Waals fluid. The van der Waals contribution captures excluded volume and cohesive attraction between polymer chains. Under sufficient tension, the material undergoes a phase transition from a dense state to a rare one — analogous to a liquid boiling. The void isn’t an elastic instability. It’s a cohesive instability. The material separates from itself.

This framing predicts something the elastic theory cannot: the aspect ratio of the adhesive layer controls whether you get a few large cavities or many small ones. Thin layers produce many small cavities; thick layers produce few large ones. The geometry of the confinement determines the pattern of failure.

The through-claim is sharp. Treating a solid as a confined fluid rather than an elastic body changes which failures are possible. The void doesn’t require a defect because it’s not a rupture — it’s a phase separation. The material isn’t breaking. It’s deciding, locally, to stop being dense.