Star-polymers represent the case where linear polymers are attached to a central core particle. The molecular weight of a star-polymer can be varied by altering the number of arms and/or the length of each arm. Star-polymers are similar to polymer-tethered nanoparticles in the limit where the nanoparticle size is very small. Accordingly, we study how the properties of pure-polymer melts are altered by adding a small fraction of star-polymers. We study star-polymer/polymer composites by employing molecular dynamic simulations. We quantify how a small fraction of added star-polymer changes the dynamics and glass transition of a bulk pure-polymer material and how these changes depend on the number and length of star arms plus intra-star molecular interactions. We find star-polymers are most effective at altering the polymer dynamics when the stars adopt expanded \"fluffy\" conformations, which can be affected by topology and the internal star interactions. We rationalize these effects by relating the glass transition temperatures to high-temperature activation energy parameters. 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 enhance or diminish the changes that arise from confinement in the film geometry. Thus, star-polymers appear to be a promising route to rationally control property changes in bulk and confined polymer materials.
"},{"label":"Degree","value":["Bachelor of Arts with Departmental Honors"]},{"label":"Administrative Note","value":"Drupal Node ID: 24227