Center for Functional Nanomaterials Seminar

Understanding the static and dynamic properties of ring polymer melts is one of the remaining challenges in polymer science. Unlike linear polymers, the topological constraints for cyclic polymers are permanent and this affects both their static and dynamic properties. Molecular dynamics simulations were conducted to investigate the structural and dynamic properties of melts of nonconcatenated ring polymers. The largest rings considered were composed of N=1600 monomers which corresponds to roughly 57 entanglement lengths for comparable linear polymers. For the rings, the radius of gyration squared was found to scale like N to the 4/5 power for an intermediate regime and N to the 2/3 power for the larger rings, indicating an overall globular conformation. The ring melts were found to diffuse much faster than their linear counterparts with the self-diffusion coefficient for both architectures obeying a N to the -2.4 scaling law for large N. Rouse and reptation theory are unable to account for the center-of-mass motion of the rings. The rings relax stress faster than linear polymers and their zero-shear viscosity was found to vary as approximately N to the 1.2 power which is much weaker than the N to the 3.4 behavior of linear chains. Lastly, the addition of a small number of linear contaminants to the ring melts was found to have a substantial effect on their rheological properties. The results for the pure ring melts may have important consequences for the understanding of the packing of chromatin fibers in the nucleus of higher eukaryotes.