Effect of constraints on the equilibrium swelling of rubber vulcanizates

The swelling of natural rubber vulcanizates under equal two‐dimensional compression has been investigated. The degree of crosslinking of the vulcanizate and the nature of the swelling liquid have both been varied. The reduction in equilibrium swelling produced by the stresses is found to agree well with theoretical predictions, except for high degrees of swelling. This divergence from theory has been explained on the basis of surface instability, which takes the form of wrinkles of the rubber surface.