Microscopic Description of Entanglements in Polyethylene Networks and Melts: Strong, Weak, Pairwise, and Collective Attributes

Abstract

We present atomistic molecular dynamics simulations of two Polyethylene systems where all entanglements are trapped: a perfect network, and a melt with grafted chain ends. We examine microscopically at what level topological constraints can be considered as a collective entanglement effect, as in tube model theories, or as certain pairwise uncrossability interactions, as in slip-link models. A pairwise parameter, which varies between these limiting cases, shows that, for the systems studied, the character of the entanglement environment is more pairwise than collective. We employ a novel methodology, which analyzes entanglement constraints into a complete set of pairwise interactions, similar to slip links. Entanglement confinement is assembled by a plethora of links, with a spectrum of confinement strengths, from strong to weak. The strength of interactions is quantified through a link `persistence', which is the fraction of time for which the links are active. By weighting links according to their strength, we show that confinement is imposed mainly by the strong ones, and that the weak, trapped, uncrossability interactions cannot contribute to the low frequency modulus of an elastomer, or the plateau modulus of a melt. A self-consistent scheme for mapping topological constraints to specific, strong binary links, according to a given entanglement density, is proposed and validated. Our results demonstrate that slip links can be viewed as the strongest pairwise interactions of a collective entanglement environment. The methodology developed provides a basis for bridging the gap between atomistic simulations and mesoscopic slip link models.

published in Macromolecules, 17 pages, 19 figures, 1 table, 123 references, 7 appendices, Supporting Information, 15 videos (two references added)

References in corpus (7)

• Topological versus rheological entanglement length in primitive path analysis protocols
• Viscoelasticity and primitive path analysis of entangled polymer liquids: From f-actin to polyethylene
• Structure and dynamics of ring polymers: entanglement effects because of solution density and ring topology
• Detailed Balance Condition and Effective Free Energy in the Primitive Chain Network Model
• A study of the entanglement in systems with periodic boundary conditions
• Mechanical Properties of End-crosslinked Entangled Polymer Networks using Sliplink Brownian Dynamics Simulations
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Cited by in corpus (8)

• Tensile Fracture of Welded Polymer Interfaces: Miscibility, Entanglements and Crazing
• Equation of State Based Slip Spring Model for Entangled Polymer Dynamics
• Topological Methods for Polymeric Materials: Characterizing the Relationship Between Polymer Entanglement and Viscoelasticity
• Self-Consistent-Field Study of Adsorption and Desorption Kinetics of Polyethylene Melts on Graphite and Comparison with Atomistic Simulations
• A Force-Level Theory of the Rheology of Entangled Rod and Chain Polymer Liquids. I. Tube Deformation, Microscopic Yielding and the Nonlinear Elastic Limit
• Segment-Scale, Force-Level Theory of Mesoscopic Dynamic Localization and Entropic Elasticity in Entangled Chain Polymer Liquids
• Network approach towards understanding the crazing in glassy amorphous polymers
• Beyond the Static Kuhn Length: Conformational Substructures and Relaxation Dynamics in Flexible Chains