Effect of Slip-Spring Parameters on the Dynamics and Rheology of Soft, Coarse-Grained Polymer Models

Abstract

Highly coarse-grained (hCG) linear polymer models allow for accessing long time and length scales by dissipative particle dynamics (DPD). This top-down strategy exploits the universal equilibrium behavior of long, flexible macromolecules by accounting only for the relevant interactions, such as molecular connectivity, and by parametrizing their strength via coarse-grained invariants, such as the mean-squared end-to-end distance. The description of the dynamics of long, entangled polymers, however, poses a challenge because (i) the noncrossability of the molecular backbones is not enforced by the soft interactions of an hCG model and (ii) the rheology involves multiple time and length scales, such as the Rouse-like dynamics on short scales and the reptation dynamics on long scales. One popular technique to effectively mimic the effect of entanglements in linear polymer melts via hCG models is slip-springs, and quantitative agreement with simulations that explicitly account for the noncrossability of molecular contours, experiments, and theoretical predictions has been achieved by identifying the time, length, and energy scales of the hCG model and adjusting the number of slip-springs per macromolecule. In the present work, we study how the spatial extent and the mobility of slip-springs affect the dynamics and discuss their implications in the choice of the degree of coarse-graining in computationally efficient hCG models.

Entanglements via Slip Springs with Soft, Coarse-Grained Models for Systems Having Explicit Liquid–Vapor Interfaces

“…Entanglements are dynamic entities, and, as pointed out before, one-to-one comparisons to kinks in the primitive path can be challenging. , To test the dynamics of the proposed model against those of the KG model, we focus on a rheology measurement technique known as a capillary breakup rheometer (CaBR). , Earlier works have already established that the SLSP model can accurately reproduce entanglement dynamics in the bulk. The current CaBR setup serves to demonstrate that this is also the case in the presence of a non-negligible liquid–vapor interface.…”

“…We identify the entanglement locations relative to the interface in a freestanding liquid–vapor interface using the Z1+ algorithm. 55 Although there is no direct correspondence between SLSPs and kinks in the primitive path, as the SLSPs are not necessarily seen as pairwise entanglements and their dynamical effects depend on the model parameters, 19 comparing the positions of the kinks and SLSPs offers a qualitative validation of the SLSP model.…”

“…Specifically, this counterbalance can be achieved by fostering synergistic coordination between the Kremer–Grest (KG) and SLSP models. A demonstration of this compensatory mechanism in action can be found in prior literature, as referenced in ref .…”

“…The remaining aspects of the model are adopted from refs ( 4 )( 15 ), and ( 19 ). A schematic representation of the SLSP model in the presence of a liquid–vapor interface is shown in Figure 1 .…”

“…As discussed in this work, coarse-grained simulations provide a unique means to represent entire nano-rheology systems, such as droplets or filaments, while retaining molecular information explicitly. Slip-spring (SLSP) models − ,− ,− have gradually been developed to describe the dynamics of high-molecular-weight entangled polymeric liquids. A particle-level description ensures that the dynamics of the system are captured at a molecular level, and SLSPs are introduced to mimic the effects of entanglements within the context of a highly coarse-grained representation. ,,− More specifically, a high degree of coarse-graining is generally accompanied by relying on soft non-bonded interaction potentials that do not prevent chain crossing; the artificial springs encoded in the SLSP representation serve to reintroduce topological constraints.…”