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

Abstract

Molecular dynamics simulations were conducted to investigate the dynamic properties of melts of nonconcatenated ring polymers and compared to melts of linear polymers. The longest rings were composed of N = 1600 monomers per chain which corresponds to roughly 57 entanglement lengths for comparable linear polymers. The ring melts were found to diffuse faster than their linear counterparts, with both architectures approximately obeying a D ∼ N −2.4 scaling law for large N . The mean-square displacement of the center-of-mass of the rings follows a sub-diffusive behavior for times and distances beyond the ring extension R 2 g , neither compatible with the Rouse nor the reptation model. The rings relax stress much faster than linear polymers and the zero-shear viscosity was found to vary as η 0 ∼ N 1.4±0.2 which is much weaker than the N 3.4 behavior of linear chains, not matching any commonly known model for polymer dynamics when compared to the observed mean-square displacements. These findings are discussed in view of the conformational properties of the rings presented in the preceding paper 1 .

Density effects in entangled solutions of linear and ring polymers

“…S1-S3), confirming the general tendency [7,42] of rings to relax faster than linear chains of the same size. At the same time, we provide previously unreported evidence that dispersed colloid particles of linear size exceeding the nominal mesh size of the solution show the tendency to diffuse more rapidly in ring polymers solutions than in linear polymers ones.…”

“…Chain dynamics can be appropriately characterized by considering the following three quantities [3,25,42]: the mean-square displacement of single monomers in the absolute frame (g 1 (τ )) and in the frame of the chain center of mass (g 2 (τ )), and the mean-square displacement of the chain center of mass (g 3 (τ )) at lag-time τ (Eqs. 8 for definitions), see Figs.…”

A topologically driven glass in ring polymers

“…These interchain interactions may include threadings that have been conjectured to be intimately related to the slow overall diffusion of the rings' center of mass (5,8,13,16) (see also SI Appendix, Fig. S4), an observation that is in apparent contrast with the very fast stress relaxation (6, 7), characterized by a power-law decay of the relaxation modulus GðtÞ and by a remarkable absence of the entanglement plateau that characterizes concentrated solutions of linear polymers.…”

“…Recently, it has been conjectured that ring polymers assume crumpled, segregated conformations in concentrated solution or the melt (5). On the other hand, numerical and experimental findings (5,6) suggest that rings exhibit strong intercoil correlations, which have proved difficult to address in simplified theoretical models (9)(10)(11)(12).…”

“…On the other hand, numerical and experimental findings (5,6) suggest that rings exhibit strong intercoil correlations, which have proved difficult to address in simplified theoretical models (9)(10)(11)(12). Because of this, there have been many recent attempts to rigorously characterize these interchains' interactions (13)(14)(15)(16), although a precise definition and unambiguous identification of these "threadings" in concentrated solutions of rings remains elusive.…”