Scaling laws in hierarchial systems of fractal polymeric clusters: neutron and light scattering experiments

We discuss the properties of the solution of polymeric clusters obtained near the gelation threshold by measuring their structure factor using small-angle neutron and light scattering experiments. The distribution of randomly branched clusters, described by percolation theory, leads to a hierarchical interpenetration of clusters. We point out the existence of a length dependent on concentration and characterizing the crossover between fractal and homogeneous structures. Intensity and concentration reduced variables allow us to plot a single master curve for both neutron and light scattering results. The asymptotic behaviours obey scaling laws and are analysed considering recent theoretical arguments. (orig.)