Structure and Dynamics of Critical Polymer Clusters Formed with Tetra-Armed Star-Polymers

Critical polymer clusters are massive randomly branched polymers formed near the gelation threshold. Because of their universal physical properties, such as the size distribution, mass fractal dimension, and viscoelastic properties, these clusters have drawn the great attention of many physicists. This review briefly introduces a few recent remarkable experimental results, which shed light on remaining questions of the critical clusters. The static structure and dynamics of these critical clusters were investigated using small angle neutron scattering (SANS), static light scattering (SLS), and dynamic light scattering (DLS). The reviewed studies primarily focused on the data analysis for the critical clusters in the intermediate concentrations between dilute and semidilute limits. An intermediate model developed by Bastide and Candau well ex-plained the observed static scattering profiles, indicating a coexisting state of the dilute and semidilute solutions. The dilute and semidilute features were also observed in dynamic studies as a superimposed translational motion of small dilute clusters and cooperatively diffusion of large semidilute clusters. These fundamental understanding may contribute to the applications of the critical clusters and further studies for the percolation process.