Neutron Spin Echo in Polymer Systems

Richter, D.; Monkenbusch, M.; Arbe, Arantxa; Colmenero, Juan

doi:10.1007/b106578

Cited by 232 publications

(397 citation statements)

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“…[15][16][17] We note at this point that the interchain collective dynamics, which have been measured by NSE techniques at the first maximum of S(Q) in different polymers, was always interpreted as the actual structural R-relaxation. 34 At Q ) 1.9 Å -1 , with the exception of the MC/SG and MC/ MC correlations, basically all the relaxation times are within a factor of 2. However, we can notice that both the MC/SG and MC/MC correlations have a small amplitude at this Q value.…”

Section: S S H Sg (Qt) By S I (Qt) ) S H Mc (Qt)/a H Mc (Q) the Rmentioning

confidence: 90%

Self- and Collective Dynamics of Syndiotactic Poly(methyl methacrylate). A Combined Study by Quasielastic Neutron Scattering and Atomistic Molecular Dynamics Simulations

et al. 2006

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We have investigated the molecular dynamics of syndiotactic poly(methyl methacrylate) well above the glass transition by combining quasielastic neutron scattering and fully atomistic computer simulations. The incoherent scattering measured by backscattering on a sample with deuterated ester methyl groups has revealed the single-particle motions of hydrogens in the main chain and in the R-methyl groups. Moreover, with neutron spin-echo experiments on the fully deuterated sample we have accessed the collective motions at the two first maxima of the structure factor. The simulated cell, which has been previously validated regarding the structural properties et al. Macromolecules 2006, 39, 3947], shows a dynamical behavior that, allowing a shift in temperature, reproduces very accurately all the experimental results. The combined analysis of both sets of data has shown that: (i) The segmental relaxation involving backbone atoms deviates from Gaussian behavior.(ii) The dynamics is extremely heterogeneous: in addition to the subdiffusion associated with the R-process and the methyl group rotations, we have found indications of a rotational motion of the ester side group around the main chain. (iii) At a given momentum transfer and depending on the molecular groups considered, the time scales for collective motion are spread over about 1 order of magnitude, the correlations involving the main chain decaying much more slowly than those relating side groups. (iv) At the length scale characteristic for the overall periodicity of the system (that corresponding to the first structure factor peak), the experimentally observed collective dynamics relates to the backbone motions and is of interchain character; there, coherency effects are observed for all correlations, though side groups display weaker collectivity. (v) At the second structure factor peak, coherency remains only for correlations involving the main chains.

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Section: S S H Sg (Qt) By S I (Qt) ) S H Mc (Qt)/a H Mc (Q) the Rmentioning

confidence: 90%

Self- and Collective Dynamics of Syndiotactic Poly(methyl methacrylate). A Combined Study by Quasielastic Neutron Scattering and Atomistic Molecular Dynamics Simulations

et al. 2006

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“…Thus, the mean squared displacement can equally well be obtained from FC NMR as in the case of neutron scattering [62].…”

Section: Extracting the Segmental Means Square Displacement From Intementioning

confidence: 99%

Proton spin dynamics in polymer melts: New perspectives for experimental investigations of polymer dynamics

Fatkullin

Stapf

Hofmann

et al. 2015

Journal of Non-Crystalline Solids

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“…In the reptation model the entanglement effect is modeled by a tube of diameter d $ ' ffiffiffiffiffiffi N e p along the coarse grained chain profile confining the chain motion (', monomer length; N e , number of monomers between the entanglements). The dominant motional mechanisms in this model are (i) a curvilinear version of the Rouse motion (local reptation) followed by (ii) the escape of the whole molecule from the tube at long times, the reptation process (see, e.g., [6,7]). The important question that is addressed now both by simulations [2,3,8,9] as well as by a variety of experiments on a macroscopic level [4,[10][11][12] is how these dynamics change under confinement.…”

mentioning

confidence: 99%

“…Using the space-time resolution of neutron spin echo spectroscopy (NSE) [7], here we report the first direct observation of the entanglement distances and the associated intermediate scale Rouse dynamics under confinement conditions. We present results on the single chain dynamic structure factor of poly(ethylene oxide) (PEO) confined in cylindrical nanopores of anodic alumina oxide (AAO).…”

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confidence: 99%

Direct Observation of Confined Single Chain Dynamics by Neutron Scattering

et al. 2010

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Neutron spin echo has revealed the single chain dynamic structure factor of entangled polymer chains confined in cylindrical nanopores with chain dimensions either much larger or smaller than the lateral pore sizes. In both situations, a slowing down of the dynamics with respect to the bulk behavior is only observed at intermediate times. The results at long times provide a direct microscopic measurement of the entanglement distance under confinement. They constitute the first experimental microscopic evidence of the dilution of the total entanglement density in a polymer melt under strong confinement, a phenomenon that so far was hypothesized on the basis of various macroscopic observations. DOI: 10.1103/PhysRevLett.104.197801 PACS numbers: 61.41.+e, 62.25.Àg, 78.70.Nx, 82.35.Lr Confinement effects in polymer melts may lead to unusual properties. This concerns both the chain conformation, which may be distorted, as well as chain dynamics, which may be altered due to surface interactions and changes of topology and chain self-density [1][2][3][4]. The understanding of such behavior is not only a scientific challenge but is also important for knowledge-based applications in nanotechnology, such as nanocomposites, coatings, adhesives, etc. [5]. Today, microscopic studies on the chain dynamics under confinement are mainly available through simulations. Only a few experiments have addressed this problem, e.g., the flow of polymers through nanopores, the extensional rheology of nanosized polymer films, the observation of dewetting kinetics of thin films or NMR relaxometry. Chain dynamics is commonly described in terms of the Rouse and the reptation model. The relaxation of the Rouse modes, determined by a balance of viscous and entropic forces, only depends on the chain length and the monomeric friction. In addition, long polymers heavily interpenetrate each other and mutually restrict their motions at long times in forming topological constraints (''entanglements''). In the reptation model the entanglement effect is modeled by a tube of diameter d $ ' ffiffiffiffiffiffi N e p along the coarse grained chain profile confining the chain motion (', monomer length; N e , number of monomers between the entanglements). The dominant motional mechanisms in this model are (i) a curvilinear version of the Rouse motion (local reptation) followed by (ii) the escape of the whole molecule from the tube at long times, the reptation process (see, e.g., [6,7]). The important question that is addressed now both by simulations [2,3,8,9] as well as by a variety of experiments on a macroscopic level [4,[10][11][12] is how these dynamics change under confinement.Basically all simulations available indicate that confinement reduces chain mobility independent of the adhesive potential of the wall. An analysis of the Rouse modes of unentangled chains under confinement reveals a uniform slowing down of all modes which was interpreted by an effective increase of monomeric friction [8]. The consequences for the entanglement density are less...

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Neutron Spin Echo in Polymer Systems

Cited by 232 publications

References 8 publications

Self- and Collective Dynamics of Syndiotactic Poly(methyl methacrylate). A Combined Study by Quasielastic Neutron Scattering and Atomistic Molecular Dynamics Simulations

Self- and Collective Dynamics of Syndiotactic Poly(methyl methacrylate). A Combined Study by Quasielastic Neutron Scattering and Atomistic Molecular Dynamics Simulations

Proton spin dynamics in polymer melts: New perspectives for experimental investigations of polymer dynamics

Direct Observation of Confined Single Chain Dynamics by Neutron Scattering

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