The Experts below are selected from a list of 6318 Experts worldwide ranked by ideXlab platform
Jianqi Wang - One of the best experts on this subject based on the ideXlab platform.
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Reexamination of the Origin of Slow Relaxation in Semidilute Polymer Solutions—Reptation Related or Not?
Macromolecules, 2016Co-Authors: Jianqi WangAbstract:The origin of the slow relaxation observed in dynamic laser light scattering (LLS) measurements of semidilute polymer solutions remains controversial. Even though the chain Reptation is invisible in dynamic LLS, the slow relaxation was still attributed to the Reptation induced density fluctuation by those who believe that there is no other slow relaxation except the Reptation. To clarify such a point, we purposely studied dynamics of semidilute solutions of narrowly distributed 4-arm star polystyrene (Mw = 1.1 × 105 g/mol and Mw/Mn = 1.02) chains in cyclohexane, wherein the chains are not entangled but topologically constrained. Our results reveal that there still exists a slow relaxation mode besides a fast one that is related to the diffusion of short chain segments (“blobs”) in the semidilute regime, clearly excluding its possible Reptation origin. The average diffusion coefficient (⟨Df⟩) and scattering intensity (⟨If⟩) related to the fast mode are scaled to the polymer concentration (C) as ⟨Df⟩ ∼ C0.5...
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reexamination of the origin of slow relaxation in semidilute polymer solutions Reptation related or not
Macromolecules, 2016Co-Authors: Jianqi WangAbstract:The origin of the slow relaxation observed in dynamic laser light scattering (LLS) measurements of semidilute polymer solutions remains controversial. Even though the chain Reptation is invisible in dynamic LLS, the slow relaxation was still attributed to the Reptation induced density fluctuation by those who believe that there is no other slow relaxation except the Reptation. To clarify such a point, we purposely studied dynamics of semidilute solutions of narrowly distributed 4-arm star polystyrene (Mw = 1.1 × 105 g/mol and Mw/Mn = 1.02) chains in cyclohexane, wherein the chains are not entangled but topologically constrained. Our results reveal that there still exists a slow relaxation mode besides a fast one that is related to the diffusion of short chain segments (“blobs”) in the semidilute regime, clearly excluding its possible Reptation origin. The average diffusion coefficient (⟨Df⟩) and scattering intensity (⟨If⟩) related to the fast mode are scaled to the polymer concentration (C) as ⟨Df⟩ ∼ C0.5...
J. Des Cloizeaux - One of the best experts on this subject based on the ideXlab platform.
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Polymer melts: a theoretical justification of double Reptation
Journal de Physique I, 1993Co-Authors: J. Des CloizeauxAbstract:The concept of double Reptation in polymer melts is supported by experiment and seems to be logical. However the dissymetry of the disentanglement process cannot be denied, and therefore double Reptation has to be proven. This is done here in the framework of two models in which either the polymer is fixed at stress points or it may slip through these points. The results can be summarized in the same way: the stress relaxation function is proportional to the density of polymer segments limited by stress points. These points can be relaxed either by Reptation or by «tube release»
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Relaxation of entangled and partially entangled polymers in melts : time-dependent Reptation
Macromolecules, 1992Co-Authors: J. Des CloizeauxAbstract:The Reptation theory founded on time-dependent diffusion and double Reptation and valid for high masses inthe entanglement domain is extended to lower masses in the region where Reptation and Rouse relaxation interfere. Equations describe relaxation in each domain separately and a theory which incorporates them is constructed. The loss modulus G(ω) is compared with experiments for polystyrene, polybutadiene, poly(methyl methacrylate) and polyisoprene. The corresponding viscosities are calculated for polystyrene and polybutadiene. All these comparisons lead to a good agreement.
Erwin Frey - One of the best experts on this subject based on the ideXlab platform.
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Disentangling entanglements in biopolymer solutions
Nature Communications, 2018Co-Authors: Philipp Lang, Erwin FreyAbstract:Reptation theory has been highly successful in explaining the unusual material properties of entangled polymer solutions. It reduces the complex many-body dynamics to a single-polymer description, where each polymer is envisaged to be confined to a tube through which it moves in a snake-like fashion. For flexible polymers, Reptation theory has been amply confirmed by both experiments and simulations. In contrast, for semiflexible polymers, experimental and numerical tests are either limited to the onset of Reptation, or were performed for tracer polymers in a fixed, static matrix. Here, we report Brownian dynamics simulations of entangled solutions of semiflexible polymers, which show that curvilinear motion along a tube (Reptation) is no longer the dominant mode of dynamics. Instead, we find that polymers disentangle due to correlated constraint release, which leads to equilibration of internal bending modes before polymers diffuse the full tube length. The physical mechanism underlying terminal stress relaxation is rotational diffusion mediated by disentanglement rather than curvilinear motion along a tube. Reptation theory has been widely adopted to describe the dynamics of entangled polymer solution, whereby a polymer follows the curvilinear Brownian motion along a tube. Here, the authors challenge this theory by showing long-time dynamics of semi-flexible polymers modulated by topological constraints.
Jimmy W. Mays - One of the best experts on this subject based on the ideXlab platform.
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Direct observation of Reptation at polymer interfaces
Nature, 1993Co-Authors: Thomas P. Russell, Vaughn R. Deline, W. D. Dozier, G. P. Felcher, G. Agrawal, Richard P. Wool, Jimmy W. MaysAbstract:ALTHOUGH the diffusion of polymer chains in the liquid state can be described over long distances by classical diffusion laws, chain entanglements make a description of the short-range behaviour more complex. In the standard 'Reptation' model1,2 the polymer chains are considered to move in a curvilinear manner along their own contours, exhibiting snake-like motion through the entangled sea of surrounding molecules. This model successfully explains many observations3–13, yet no direct evidence for reptative motion has been reported. Here we describe the observation of Reptation of molecules across the interface between two types of partially deuterated polystyrene polymers. The time evolution of the hyd-rogen and deuterium profiles, determined by dynamic secondary-ion mass spectrometry, can be explained only on the basis of a Reptation model. Our results demonstrate that, despite being inevit-ably simplified, the description of polymer diffusion in terms of Reptation is essentially correct.
Philipp Lang - One of the best experts on this subject based on the ideXlab platform.
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Disentangling entanglements in biopolymer solutions
Nature Communications, 2018Co-Authors: Philipp Lang, Erwin FreyAbstract:Reptation theory has been highly successful in explaining the unusual material properties of entangled polymer solutions. It reduces the complex many-body dynamics to a single-polymer description, where each polymer is envisaged to be confined to a tube through which it moves in a snake-like fashion. For flexible polymers, Reptation theory has been amply confirmed by both experiments and simulations. In contrast, for semiflexible polymers, experimental and numerical tests are either limited to the onset of Reptation, or were performed for tracer polymers in a fixed, static matrix. Here, we report Brownian dynamics simulations of entangled solutions of semiflexible polymers, which show that curvilinear motion along a tube (Reptation) is no longer the dominant mode of dynamics. Instead, we find that polymers disentangle due to correlated constraint release, which leads to equilibration of internal bending modes before polymers diffuse the full tube length. The physical mechanism underlying terminal stress relaxation is rotational diffusion mediated by disentanglement rather than curvilinear motion along a tube. Reptation theory has been widely adopted to describe the dynamics of entangled polymer solution, whereby a polymer follows the curvilinear Brownian motion along a tube. Here, the authors challenge this theory by showing long-time dynamics of semi-flexible polymers modulated by topological constraints.
