Microscopic Picture of Constraint Release Effects in Entangled Star Polymer Melts

Abstract

The constraint release (CR) effect in entangled branched polymers is generally described by the widely accepted Dynamic Tube Dilation (DTD) theory based on the tube model, which predicts the stress relaxation function reasonably well, but not the dielectric or arm end-to-end vector relaxation. The microscopic picture of entanglement dynamics even in the simple case of star polymers is still not fully resolved. In this * To whom correspondence should be addressed entanglements sitting on a target star arm, only those destroyed by the arm free end dominate the arm end-to-end vector relaxation, while the constraint release events produce an accelerated drift of the mean positions of these specific entanglements towards the arm-end, which is an essential mechanism for understanding the relaxation of star polymers in concentrated solutions or melts. Our findings call for an examination of the microscopic foundation of conventional DTD picture and inspire the development of quantitative theories with consideration of more microscopic details.

Surface Disentanglement and Slip in a Polymer Melt: A Molecular Dynamics Study

“…It would be interesting to investigate the behavior of dynamic definitions of entanglements [16,61] away from equilibrium, and their relation to primitive path kinks, even for true bulk chains. At equilibrium, the survival probability of 'long lived close contacts' has been demonstrated to be proportional to the linear stress relaxation function [18]. However such dynamic measures of entanglements are computationally expensive to investigate for non-equilibrium cases.…”

“…There is much evidence for a binary picture of entanglements [15][16][17][18]. In line with this picture, we are particularly interested in identifying the number and behavior of topological interactions between grafted (tethered -T) and non-grafted (free -F) chains away from equilibrium.…”

Entanglement dynamics at flat surfaces: Investigations using multi-chain molecular dynamics and a single-chain slip-spring model

“…The observed ratio implies that entanglements are predominately binary events, roughly in agreement with a detailed investigation using Molecular Dynamics which nevertheless showed that a smaller but significant number of entanglements involve three chains 26 . There is also evidence for the dominance of binary entanglements in simulations of star 27 and ring 28 chain architectures. Here a relevant question is whether the binary picture is also valid for confined melts.…”

5D Entanglement in Star Polymer Dynamics

“…[9,10] They are already used as additives in consumer products (viscosity modifiers, defoaming agents) and in biomedical research as drug delivery vehicles. [19,20] In this work we present a multi-chain simulation running over a 100 times faster than the best supercomputer result of a comparable star polymer problem published to date. [13][14][15] Its main outcome is the exponential growth of the relaxation time τ a ∝ e N/Na , where N a is the arm length at the onset of star dynamics.…”

“…[18] The current consensus is in favor of arm retraction, although a broad mesoscopic time range remains unexplored and some open questions remain. [19,20] In this work we present a multi-chain simulation running over a 100 times faster than the best supercomputer result of a comparable star polymer problem published to date. [18] The speedup quoted here is an order-of-magnitude estimate, whose precise value cannot be guaranteed, as it depends on the specific hardware, driver, compiler, and kernel optimization, the random number generator, as well as details of the physical model such as the algorithm used to constrain the bond length and (optionally) the bond stiffness.…”