Molecular Motion in Solid State Polymers

Saitô, Nobuhiko; Okano, Kōji; Iwayanagi, Shigeo; Hideshima, Teruo

doi:10.1016/s0081-1947(08)60262-3

Cited by 71 publications

(20 citation statements)

References 254 publications

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“…Above the electrical percolation we have a fully formed network that has provided all the nucleation activity that is capable of and with In comparison to polyethylene [80][81][82], the mechanical α-relaxation of polypropylene is less investigated. The common view is that the origin of this transition can be associated to relaxations on both the amorphous and the crystalline phases of the matrix, with the overall relaxation divided into two separate ones α 1 and α 2 that are located at lower and higher temperatures respectively [83]. The exact origin of the different relaxations is still under investigation, but it is believed that both α 1 and α 2 can be associated with specific intralamellar motions and other intracrystalline processes, originating from the existence of anisotropies on the crystal lattice potential [84].…”

Section: Dmtamentioning

confidence: 99%

Melt-Mixed 3D Hierarchical Graphene/Polypropylene Nanocomposites with Low Electrical Percolation Threshold

et al. 2019

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Graphene-based materials are a family of carbonaceous structures that can be produced using a variety of processes either from graphite or other precursors. These materials are typically a few layered sheets of graphene in the form of platelets and maintain some of the properties of pristine graphene (such as two-dimensional platelet shape, aspect ratio, and graphitic bonding). In this work we present melt mixed graphene-based polypropylene systems with significantly reduced percolation threshold. Traditionally melt-mixed systems suffer from poor dispersion that leads to high electrical percolation values. In contrast in our work, graphene was added into an isotactic polypropylene matrix, achieving an electrical percolation threshold of~1 wt.%. This indicates that the filler dispersion process has been highly efficient, something that leads to the suppression of the β phase that have a strong influence on the crystallization behavior and subsequent thermal and mechanical performance. The electrical percolation values obtained are comparable with reported solution mixed systems, despite the use of simple melt mixing protocols and the lack of any pre or post-treatment of the final compositions. The latter is of particular importance as the preparation method used in this work is industrially relevant and is readily scalable.

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Section: Dmtamentioning

confidence: 99%

Melt-Mixed 3D Hierarchical Graphene/Polypropylene Nanocomposites with Low Electrical Percolation Threshold

et al. 2019

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“…However, we (and many others [76,58,85,64,67,59,41,86,87,71,69,88,89,90,77,69,91,50]) have preferred to use the classical unconstrained model as a reference to be able to assess the influence of the imposition of constraints in an incremental way consisting of a series of controlled steps. Although some works have advocated the point of view that the proper justification of constrained models should come from a quantum mechanical treatment [49,54,72,92,56,43,79,83,93,94], and the comparison to experiment [94] or to quantum mechanics is indeed more relevant in terms of the absolute accuracy of the constrained models, the approximations connecting the former to the latter are many, thus obscuring the influence of each individual step. In particular, it is worth mentioning refs.…”

Section: Flexible Vs Hard Constraintsmentioning

confidence: 99%

The canonical equilibrium of constrained molecular models

Echenique

Cavasotto

García-Risueño

2011

Eur. Phys. J. Spec. Top.

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Abstract. In order to increase the efficiency of the computer simulation of biological molecules, it is very common to impose holonomic constraints on the fastest degrees of freedom; normally bond lengths, but also possibly bond angles. Since the maximum time step required for the stability of the dynamics is proportional to the shortest period associated with the motions of the system, constraining the fastest vibrations allows to increase it and, assuming that the added numerical cost is not too high, also increase the overall efficiency of the simulation. However, as any other element that affects the physical model, the imposition of constraints must be assessed from the point of view of accuracy: both the dynamics and the equilibrium statistical mechanics are model-dependent, and they will be changed if constraints are used. In this review, we investigate the accuracy of constrained models at the level of the equilibrium statistical mechanics distributions produced by the different dynamics. We carefully derive the canonical equilibrium distributions of both the constrained and unconstrained dynamics, comparing the two of them by means of a "stiff" approximation to the latter. We do so both in the case of flexible and hard constraints, i.e., when the value of the constrained coordinates depends on the conformation and when it is a constant number. We obtain the different correcting terms associated with the kinetic energy mass-metric tensor determinants, but also with the details of the potential energy in the vicinity of the constrained subspace (encoded in its first and second derivatives). This allows us to directly compare, at the conformational level, how the imposition of constraints changes the thermal equilibrium of molecular systems with respect to the unconstrained case. We also provide an extensive review of the relevant literature, and we show that all models previously reported can be considered special cases of the most general treatments presented in this work. Finally, we numerically analyze a simple methanol molecule in order to illustrate the theoretical concepts in a practical case.

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“…If we assume that Tg of PSHD corresponds to the temperature at which the tan i'J curve deviates from the background, ilHa of the a peak at its peak temperature is evaluated by eq 4. The method for determining T g was described first by Hideshima et al, 7 and is conveniently used for PSHD samples with various copolymer compositions. Its principle is based on the assumption that the beginning of any thermal motion associated with the micro-Brownian movement is reflected in the rise of the tan i'J curve of the a peak.…”

Section: Dynamic Viscoelasticitymentioning

confidence: 99%

Solid State Properties of Poly(spiro[2,4]hepta-4,6-diene)

Sugimoto

Takayanagi

Kunitake

1977

Polym J

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Poly(spiro[2,4]hepta-4,6-diene) (PSHD) is considered to behave like a rigid rod on the basis of the unusually large index (a=l.7) in the viscosity-molecular weight relationship. Thus, some solid state properties were investigated with PSHD samples which contained different ratios of the 1,2-and 1,4-addition units. The thermo-mechanical curve of solvent-cast films showed that there were two tan ii peaks below 300°C. The /3 peak was located at about 130°C (110 Hz), and affected little by the polymer composition. On the other hand, the position of the a peak shifted linearly from 200°C to 300°C with increasing fraction of the 1,4-unit, and the peak height decreased simultaneously. A loss peak associated with thermal decomposition and/or crosslinking was found at temperatures above 300°C. The TGA curve revealed that the thermal decomposition of PSHD takes place at about 300°C in air and at about 400°C under nitrogen. An exothermic peak was found in the same temperature range in the DSC curve. The crosslinked specimen showed no loss peak in dynamic measurements, which reflected immobilization of the molecule by crosslinks. The PSHD film did not show any indication of crystallinity.

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Molecular Motion in Solid State Polymers

Cited by 71 publications

References 254 publications

Melt-Mixed 3D Hierarchical Graphene/Polypropylene Nanocomposites with Low Electrical Percolation Threshold

Melt-Mixed 3D Hierarchical Graphene/Polypropylene Nanocomposites with Low Electrical Percolation Threshold

The canonical equilibrium of constrained molecular models

Solid State Properties of Poly(spiro[2,4]hepta-4,6-diene)

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