Structure and Dynamics of Star-polymer/Polymer Composites

Star polymers are simple extensions of linear polymers, where molecular weight can be varied by altering the number of arms or the length of each arm. Star polymers are also similar to polymer-tethered nanoparticles in the limit where the nanoparticle size becomes very small.  Accordingly, we study how the properties of polymer melts are altered by the addition of a small fraction of star polymer, thereby creating a star polymer/polymer composites.  Using molecular simulation, we quantify how a small fraction of added star polymer changes the dynamics and glass transition of a polymer material, and how these changes depend on the number and length of star arms, as well as the intra-star molecular interactions.  We find star polymers are most effective at altering the polymer dynamics when the stars have adopt more expanded, of "fluffy" conformation, which can be affected both by topology and the internal star interactions.  We extend these observations to the case of ultra-thin composite films, where the stars potentially preferentially segregate to one of the interfaces, which can serve to enhance or diminish the changes that arise from confinement in the film geometry.  Thus, star-polymer appear to be a promising route to rationally control property changes in bulk and confined polymer materials.