STRUCTURE AND SWELLING OF END-LINKED MODEL NETWORKS

In the framework of the three-dimensional bond-fluctuation model, the formation and swelling of end-linked monodisperse polymer networks is simulated. The kinetics of cross-linking show a cross-over from reaction-controlled to diffusion-limited behaviour, depending on the reaction rate. On small scales the internal dimension of the resulting networks is ca. 1.3 while on large scales it adopts the dimension of 3. The cross-over between both regions can be interpreted as a back-folding mechanism leading to internal dimensions larger than 3 at intermediate scales. The same behaviour was previously obtained by simulating randomly cross-linked networks. In marked contrast to some theoretical models, the networks deform in a highly non-affine manner upon swelling. Small substructures swell much less than the whole sample as determined from the occupation density at the centre of the simulation lattice. More precisely, the swelling degree is a monotonically increasing function of the scale under consideration. This can be related to the unfolding of the network structure at scales much larger than a single precursor chain.