Autoadhesion of Glassy Polymers

Boiko, Yuri M.

doi:10.1002/masy.201250609

Cited by 8 publications

(5 citation statements)

References 28 publications

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“…Recently, McGraw et al [21] have performed crazing measurements to probe the interdiffusion between two thin films of entangled polymers and showed that it takes less than one bulk reptation time to observe the structural characteristics of bulk crazes at the interface. Similar conclusions about the recovery of interfacial strength have been obtained from lap-joint shear tests [22][23][24][25]. These studies determined the ultimate shear stress at failure and correlated it with interdiffusion time.…”

supporting

confidence: 68%

“…As in previous simulations [32], we determined the interfacial strength using a shear test that is similar to a lap-joint shear experiment [22][23][24][25]. To focus on a region of width H near the interface, atoms in top (z > H/2) and bottom (z < −H/2) layers were held rigid and displaced at constant velocity in opposite directions in the xy−plane.…”

Section: Interface Simulationsmentioning

confidence: 99%

“…Recently, we have probed the interfacial strength of polymer interfaces in our molecular dynamics simulations [32,33] using a shear test that is similar to lapjoint shear experiments [22][23][24][25]. For miscible polymers, the interfacial strength increases with interdiffusion time, and saturates at the bulk strength.…”

mentioning

confidence: 99%

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Healing of polymer interfaces: Interfacial dynamics, entanglements, and strength

Robbins

Perahia

et al. 2014

Phys. Rev. E

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Self-healing of polymer films often takes place as the molecules diffuse across a damaged region, above their melting temperature. Using molecular dynamics simulations we probe the healing of polymer films and compare the results with those obtained for thermal welding of homopolymer slabs. These two processes differ from each other in their interfacial structure since damage leads to increased polydispersity and more short chains. A polymer sample was cut into two separate films that were then held together in the melt state. The recovery of the damaged film was followed as time elapsed and polymer molecules diffused across the interface. The mass uptake and formation of entanglements, as obtained from primitive path analysis, are extracted and correlated with the interfacial strength obtained from shear simulations. We find that the diffusion across the interface is significantly faster in the damaged film compared to welding because of the presence of short chains. Though interfacial entanglements increase more rapidly for the damaged films, a large fraction of these entanglements are near chain ends. As a result, the interfacial strength of the healing film increases more slowly than for welding. For both healing and welding, the interfacial strength saturates as the bulk entanglement density is recovered across the interface. However, the saturation strength of the damaged film is below the bulk strength for the polymer sample. At saturation, cut chains remain near the healing interface. They are less entangled and as a result they mechanically weaken the interface. Chain stiffness increases the density of entanglements, which increases the strength of the interface. Our results show that a few entanglements across the interface are sufficient to resist interfacial chain pullout and enhance the mechanical strength.

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supporting

confidence: 68%

Section: Interface Simulationsmentioning

confidence: 99%

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Healing of polymer interfaces: Interfacial dynamics, entanglements, and strength

Robbins

Perahia

et al. 2014

Phys. Rev. E

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“…In recent work, we have used simulations to follow the evolution of the shear strength of interfaces between miscible and immiscible polymers . The maximum shear stress before failure σ max was evaluated using a geometry that mimics a lap-joint shear experiment. − As in experiments, we found that σ max rose with welding time t as t 1/4 and saturated long before polymers had diffused by their radius of gyration. In contrast to experiments, simulations allowed direct observations of the evolution of topological constraints (TCs) associated with entanglements.…”

Section: Introductionmentioning

confidence: 86%

Tensile Fracture of Welded Polymer Interfaces: Miscibility, Entanglements, and Crazing

Grest

Robbins

2014

Macromolecules

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Large-scale molecular simulations are performed to investigate tensile failure of polymer interfaces as a function of welding time t. Changes in the tensile stress, mode of failure and interfacial fracture energy G I are correlated to changes in the interfacial entanglements as determined from Primitive Path Analysis. Bulk polymers fail through craze formation, followed by craze breakdown through chain scission. At small t welded interfaces are not strong enough to support craze formation and fail at small strains through chain pullout at the interface. Once chains have formed an average of about one entanglement across the interface, a stable craze is formed throughout the sample. The failure stress of the craze rises with welding time and the mode of craze breakdown changes from chain pullout to chain scission as the interface approaches bulk strength. The interfacial fracture energy G I is calculated by coupling the simulation results to a continuum fracture mechanics model. As in experiment, G I increases as * To whom correspondence should be addressed † Johns Hopkins University ‡ University of North Carolina ¶ Sandia National Laboratories 1 arXiv:1410.1917v1 [cond-mat.soft] 7 Oct 2014 t 1/2 before saturating at the average bulk fracture energy G b . As in previous simulations of shear strength, saturation coincides with the recovery of the bulk entanglement density. Before saturation, G I is proportional to the areal density of interfacial entanglements. Immiscibiltiy limits interdiffusion and thus suppresses entanglements at the interface. Even small degrees of immisciblity reduce interfacial entanglements enough that failure occurs by chain pullout and

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“…It is known to depend on entanglement formation through diffusion of the chains across the interface, − ,− which can be described by the well-known reptation model . Accordingly, a strong dependence of adhesive fracture toughness ( G α ) on molecular weight ( M w ) and welding time ( t w ) is observed. ,,,− Typically, for the adhesive-fracture toughness to reach the value of the bulk-fracture toughness, welding times on the order of the reptation time are needed, which can be excessively long for ultrahigh molecular weight polymers, as the reptation time scales with the third power of the molecular weight. ,, Welding of semicrystalline polymers that have a glass-transition temperature below room temperature can deviate from the classical reptation approach due to an initial nonequilibrium conformation of the chains. ,− Furthermore, in such materials, the contribution of entanglement formation due to self-diffusion of the polymer chains to the adhesive-fracture toughness below the melting temperature can be partly obscured by cocrystallization of the macromolecular chains across the interface, but full recovery remains a slow process. ,,, …”

Section: Introductionmentioning

confidence: 99%

“Tying the Knot”: Enhanced Recycling through Ultrafast Entangling across Ultrahigh Molecular Weight Polyethylene Interfaces

et al. 2021

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Ultrahigh molecular weight polyethylene (UHMWPE) is a high-end engineering polymer. However, the very features that lead to its exceptional properties, i.e., ultralong macromolecular chains, render joining two surfaces of this material a tedious and slow process, leading to long welding times and impeding mechanical recycling of UHMWPE.Here we report the anomalous fast joining of UHMWPE interfaces by simply depositing small amounts of nascent disentangled UHMWPE powder at the interface. The time evolution of buildup of adhesive fracture energy in the molten state and the reduction in interfacial slip between two molten UHMWPE layers reveal an orders of magnitude increase of the rate of interpenetration compared to the dynamics of a regular UHMWPE−melt interface. This ultrafast self-diffusion mechanism is insensitive to molecular weight, in contrast to reptation-driven diffusion, and provides a direct indication of the entropy-driven "chain explosion" upon melting of nascent disentangled UHMWPE. The usefulness of fast molecular stitching is demonstrated for enhanced recycling of UHMWPE.

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Autoadhesion of Glassy Polymers

Cited by 8 publications

References 28 publications

Healing of polymer interfaces: Interfacial dynamics, entanglements, and strength

Healing of polymer interfaces: Interfacial dynamics, entanglements, and strength

Tensile Fracture of Welded Polymer Interfaces: Miscibility, Entanglements, and Crazing

“Tying the Knot”: Enhanced Recycling through Ultrafast Entangling across Ultrahigh Molecular Weight Polyethylene Interfaces

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