Rheology of Ring Polymer Melts: From Linear Contaminants to Ring-Linear Blends

Abstract

Ring polymers remain a challenge to our understanding of polymer dynamics. Experiments are difficult to interpret because of the uncertainty in the purity and dispersity of the sample. Using both equilibrium and nonequilibrium molecular dynamics simulations we have investigated the structure, dynamics, and rheology of perfectly controlled ring-linear polymer blends of chains of up to about 14 entanglements per chain, comparable to experimental systems. Linear contaminants increase the zero-shear viscosity of a ring polymer melt by about 10% around one-fifth of their overlap concentration. For equal concentrations of linear and ring polymers, the blend viscosity is about twice that of the pure linear melt. The diffusion coefficient of the rings decreases dramatically, while the linear polymers are mostly unaffected. Our results are supported by a primitive path analysis.

Molecular dynamics simulation study of nonconcatenated ring polymers in a melt. II. Dynamics

“…The viscosity measurements for the rings and linear systems have been confirmed by nonequilibrium molecular dynamics simulations 38 . These results will appear in an upcoming paper 39 . The zero-shear viscosities are given for the rings and linear systems in Table I.…”

“…To better compare our findings to experiments, a systematic study of the influence of linear "contaminants" is needed since experiments never can exclude them completely. Such a study is in preparation 39 and will also include an extensive analysis of the dynamic scattering functions of both the rings and the linear polymers. Recent advances in synthesis, purification and characterization should allow a better comparison in the near future.…”

Challenges in Multiscale Modeling of Polymer Dynamics

“…Therefore, including the bending potential into the FENE model is a very common extension [16,[121][122][123]. For example, the FENE model with finite bending stiffness has been applied to study the static structure and dynamics of ring polymers [124][125][126]. Aside from including a bending potential, there have now been a number of studies of the FENE model where the cutoff has been increased to include the attractive well, i.e., r cutoff =1.5∼2.5 σ.…”

Topological Interactions in Ring Polymers

“…to find a state in which these topological interactions can drive a dynamically arrested state, or a "topological glass". In this respect, a melt of rings is a more promising candidate than, for instance, a blend of rings contaminated with linear chains [Halverson et al, 2012]. Although such a system has showed a surprising rubbery plateau even after small addition of linear contaminants, there are no topological constraints that can be imposed on linear polymers, and for this reason, the largest relaxation time of the system is bound above by the slowest relaxation of the linear polymers, i.e.…”