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

Kirk, Jack; Kröger, Martin; Ilg, Patrick

doi:10.1021/acs.macromol.8b01865

Cited by 11 publications

(5 citation statements)

References 69 publications

(217 reference statements)

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“…Our results for a liquid–vapor interface are similar to those reported by Kirk et al − for polymers confined by a wall. Those studies demonstrated that the interface has no significant impact on the number of kinks near the interface and that a SLSP model can reproduce these findings accurately.…”

Section: Resultssupporting

confidence: 92%

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

Schneider,

de Pablo

2023

Macromolecules

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Recent advances in nano-rheology require that new techniques and models be developed to precisely describe the equilibrium and non-equilibrium characteristics of entangled polymeric materials and their interfaces at a molecular level. In this study, a slip-spring (SLSP) model is proposed to capture the dynamics of entangled polymers at interfaces, including those between liquids, liquids and vapors, and liquids and solids. The SLSP model employs a highly coarse-grained approach, which allows for comprehensive simulations of entire nano-rheological characterization systems using a particle-level description. The model relies on many-body dissipative particle dynamics (MDPD) non-bonded interactions, which permit explicit description of liquid−vapor interfaces; a compensating potential is introduced to ensure an unbiased representation of the shape of the liquid−vapor interface within the SLSP model. The usefulness of the proposed MDPD + SLSP approach is illustrated by simulating a capillary breakup rheometer (CaBR) experiment, in which a liquid droplet splits into two segments under the influence of capillary forces. We find that the predictions of the MDPD + SLSP model are consistent with experimental measurements and theoretical predictions. The proposed model is also verified by comparison to the results of explicit molecular dynamics simulations of an entangled polymer melt using a Kremer−Grest chain representation, both at equilibrium and far from equilibrium. Taken together, the model and methods presented in this study provide a reliable framework for molecular-level interpretation of high-polymer dynamics in the presence of interfaces.

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Section: Resultssupporting

confidence: 92%

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

Schneider,

de Pablo

2023

Macromolecules

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“…Slip has been shown to vary considerably with the applied shear rate, whereas in many cases the variations can be nonmonotonic due to the transition between the weak and the strong flow regimes, and the manifestation of shear-thinning and viscous-heating phenomena. 22,23,61 In situations with strong flow of high molar mass PE chains, the effective slip velocity has been shown 21,22 to rise monotonically with γȧ pp in strong flow situations, in line with the experimental measurements. 12 The simulations by Jabarzadeh et al for C 16 convey a similar picture, wherein slip decreases with increasing γȧ pp in weak flow situations (γė ff /γȧ pp increases), whereas after some point slip increases again (γė ff /γȧ pp decreases) indicating the manifestation of shear-thinning phenomena.…”

Section: Panels C and D Insupporting

confidence: 82%

Effect of Surface Nanopatterning on Slip: The Case of Couette Flow of Long-Chain Polyethylene Melt Flowing Past Gold Surfaces

2021

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The manifestation of slip during flow of a polymer melt past a solid surface depends on several parameters, such as film thickness, the strength of polymer−solid interactions compared to the cohesive energy of the polymer, and the roughness of the surface. Understanding the role of these molecular aspects for slip is crucial in microfluidics, frictiontuning, polymer extrusion, and nanocomposites applications. The present article investigates the effect of surface nanopatterning on slip, via Couette-flow simulations of long chain polyethylene melts past nanopatterned gold surfaces. Slip is quantified in terms of the true and effective slip velocity, and the slip length. When polymer chains are adsorbed to surfaces with periodic features (e.g., crystal planes), they develop preferential ordering in a way that enables them to minimize their free energy. The orientation of a chain is affected by that of its neighbors; thus, when several chains come together, they are prone to form regions with crystal-like orientation. We show that, in some cases, the introduction of nanopatterns on the surface can perturb and induce reorganization of these regions, and in turn affect slip. The nanopatterns are realized as periodic defect stripes of variable width, depth, areal density, and orientation angle. In situations in which the width of the defects becomes comparable to the diameter of individual chain backbones, slip is minimized (stick conditions). Cutting the nanopatterns in low symmetry directions can affect the quality of their edges and lead to enhanced friction. To characterize these edges we have devised a scheme for the quantification of the mean square roughness and mean position of the surface, which is general and applicable in 2 and 3 dimensions for any kind of material, either crystalline of amorphous. Applying the patterns on the opposing solid surfaces in a symmetric or antisymmetric manner has a profound effect on flow. We show that the application of nanopatterns in symmetric configurations generates zero net flow and induces additional shear along directions normal to the direction of the flow. The application of symmetry-breaking configurations can guide flow toward preferential directions, a result with possible applications in microfluidic devices.

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“…The polymer is subjected to strong flow at . , As shown in Table , the experimental conditions under which the simple shear experiment was performed caused the chains in the system to experience more stretching than chain orientation, as indicated by the magnitude of relative to and reflected by the continuous decrease in surface roughness, R q .…”

Section: Resultsmentioning

confidence: 99%

Polymer Fractionation at an Interface in Simple Shear with Slip

Kwakye-Nimo

Inn

et al. 2022

Macromolecules

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Using a sliding-plate rheometer, we subject a bimodal high-density polyethylene to simple shear flow with slip and collect the debris left on the surface. Through gel permeation chromatography analysis, we observe surface fractionation occurring in simple shear flow even in the absence of a bulk shear gradient. The surface fractionation and the thickness of the debris film showed a shear rate dependency. The enrichment/depletion transition point was found to be markedly different than that predicted thermodynamically and consistent with previous observations of fractionation on the surface of an extrudate from capillary flow. Our results also highlight the possible occurrence of both adhesive and cohesive slip failure mechanisms, especially at lower shear rates. These new insights provide additional understanding of the physics of polymer slip.

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

Cited by 11 publications

References 69 publications

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

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

Effect of Surface Nanopatterning on Slip: The Case of Couette Flow of Long-Chain Polyethylene Melt Flowing Past Gold Surfaces

Polymer Fractionation at an Interface in Simple Shear with Slip

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