Dynamical Signatures of the Vulcanization Transition

Dynamical properties of vulcanized polymer networks are addressed via a Rouse-type model that incorporates the effect of permanent random cross-links. The incoherent intermediate scattering function is computed in the sol and gel phases, and at the vulcanization transition between them. At any nonzero cross-link density within the sol phase Kohlrausch relaxation is found. The critical point is signaled by divergence of the longest time scale, and at this point the scattering function decays algebraically, whereas within the gel phase it acquires a time-persistent part identified with the gel fraction.