Potential energy in a three-dimensional vibrated granular medium measured by NMR imaging

We use molecular dynamics simulations to study the swelling of randomly end-cross-linked polymer networks in good solvent conditions. We find that the equilibrium degree of swelling saturates at Q(eq) approximately N(3/5)(e) for mean strand lengths &Nmacr;(s) exceeding the melt entanglement length N(e). The internal structure of the network strands in the swollen state is characterized by a new exponent nu = 0.72+/-0.02. Our findings can be rationalized by a Flory argument for a self-similar structure of mutually interpenetrating network strands, agree partially with the classical Flory-Rehner theory, and are in contradiction to de Gennes' c(*)-theorem.