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1.
Molecular dynamics simulation of poly(3‐hexylthiophene) helical structure In Vacuo and in amorphous polymer surrounding
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Natalia I. Borzdun Sergey V. Larin Stanislav G. Falkovich Victor M. Nazarychev Igor V. Volgin Alexander V. Yakimansky Alexey V. Lyulin Vikas Negi Peter A. Bobbert Sergey V. Lyulin 《Journal of Polymer Science.Polymer Physics》2016,54(23):2448-2456
The stability of poly(3‐hexylthiophene) (P3HT) helical structure has been investigated in vacuo and in amorphous polymer surrounding via molecular dynamics‐based simulations at temperatures below and above the P3HT melting point. The results show that the helical chain remains stable at room temperature both in vacuo and in amorphous surrounding, and promptly loses its structure at elevated temperatures. However, the amorphous surrounding inhibits the destruction of the helix at higher temperatures. In addition, it is shown that the electrostatic interactions do not significantly affect the stability of the helical structure. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2448–2456 相似文献
2.
O.M. Lyulin V.I. Perevalov H. Tran J.-Y. Mandin V. Dana L. Rgalia-Jarlot X. Thomas D. Dcatoire 《Journal of Quantitative Spectroscopy & Radiative Transfer》2009,110(17):1815-1824
Using the Fourier transform spectra of the acetylene molecule recorded near 1.5-μm, the intensities of 111 lines belonging to seven hot bands of the main isotopologue 12C2H2 have been retrieved by means of a multispectrum fitting procedure. Considering the density of lines in the spectra, and the fact that the measured bands are the weakest observed, the accuracy of the measurements is around 10%. At first stage, an empirical treatment of these data has been performed, leading to the vibrational transition dipole moment squared and some Herman–Wallis coefficients. Then the measured line intensities of this work and collected ones from the literature have been treated simultaneously within the framework of the effective operator approach. 相似文献
3.
Molecular-dynamic simulation of low-temperature plastic deformation (T
def = 50 K, T
def/T
g ≤ 0.3) is studied for glassy polymethylene under the regime of active uniaxial compression and tension for a cell composed
of 64 chains containing 100 -CH2 groups in each (as united atoms) and with periodic boundary conditions. Thirty-two such cells are created, and, in each cell,
polymethylene chains in the statistical coil conformation are independently constructed. The cells are subjected to isothermal
uniaxial compression at T
def = 50 K by ɛ = 30% and by ɛ = 70% under uniaxial tension. In the course of loading, a σ-ɛ diagram is recorded, while the mechanical
work spent on deformation, the changes in the overall potential energy of the system, and the contributions from various potential
interactions (noncovalent van der Waals bonds, chemical links, valence and torsional angles) are estimated. The results are
averaged over all 32 cells. The relaxation of stored potential energy and residual strain after complete unloading of the
deformed sample is studied. The relaxation of stored energy and residual strain is shown to be incomplete. Most of this energy
and strain is stored in the sample at the deformation temperature for long period. The conformational composition of chains
and the average density of polymer glass during loading are analyzed. Simulation results show that inelastic deformations
commence not with the conformational unfolding of coils but with the nucleation of strain-bearing defects of a nonconformational
nature. The main contribution to the energy of these defects is provided by van der Waals interactions. Strain-bearing defects
are nucleated in a polymer glass during tension and compression primarily as short-scale positive volume fluctuations in the
sample. During tension, the average density of the glass decreases; during compression, this parameter slightly increases
to ɛ ≈ 8% and then decreases. An initial increase in the density indicates that, during compression and at ɛ < 8%, coils undergo
compactization via an increase in chain packing. During compression, the concentration of trans conformers remains unchanged below ɛ ≈ 8% and then decreases. During compression, it means that in a glass, coils do not
increase their sizes at strains below ɛ ≈ 8%. During tensile drawing, coils remain unfolded below ɛ ≈ 35%; at higher strains,
coils become enriched with trans conformers or unfold. At this stage, the concentration of trans conformers linearly increases. The development of a strain-induced excess volume (strain-bearing defects) entails an increase
in the potential energy of the sample. Under the given conditions of deformation, nucleation of strain-bearing defects and
an increase in their concentration are found to be the only processes occurring at the initial stage of loading of glassy
polymethylene. The results of computer-aided simulation are compared with the experimental data reported in the literature. 相似文献
4.
O.M. Lyulin I. Morino R. Kumazawa 《Journal of Quantitative Spectroscopy & Radiative Transfer》2011,112(3):531-539
The absorption spectra of methane at different path lengths and different pressures for three temperatures 180, 240 and 296 K have been recorded in the 5556-6166 cm−1 region using the Bruker IFS 120 HR and 125 HR high-resolution Fourier transform spectrometers. The multispectrum fitting procedure has been applied to these spectra to recover the spectral line parameters. The main goal of this procedure was the determination of self-broadening and self-pressure-induced shift coefficients and the exponents of their temperature dependences. These parameters have been derived for 406 assigned lines with good values of the signal to noise ratio. The rotational dependence of these parameters is discussed. 相似文献
5.
Parameterization of electrostatic interactions for molecular dynamics simulations of heterocyclic polymers
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Victor M. Nazarychev Sergey V. Larin Alexander V. Yakimansky Natalia V. Lukasheva Andrey A. Gurtovenko Iosif V. Gofman Vladimir E. Yudin Valentin M. Svetlichnyi Jose M. Kenny Sergey V. Lyulin 《Journal of Polymer Science.Polymer Physics》2015,53(13):912-923
The paper focuses on the problem of electrostatic interactions in molecular dynamics simulations of thermal properties of heterocyclic polymers. The study focuses on three thermoplastic polyimides synthesized on the basis of 1,3‐bis‐(3′,4‐dicarboxyphenoxy)benzene (dianhydride R) and three diamines: 4,4′‐bis‐(4″‐aminophenoxy) diphenylsulfone (diamine BAPS), 4,4′‐bis‐(4″‐aminophenoxy) biphenyl (diamine BAPB), and 4,4′‐bis‐(4''‐aminophenoxy) diphenyloxide (diamine BAPO). In the molecular dynamics simulations these polyimides were described by the Gromos53a5 force field. To parameterize the electrostatic interactions four methods of calculating the partial atomic charges were chosen: B3LYP/6–31G*(Mulliken), AM1(Mulliken), HF/6–31G*(Mulliken), and HF/6–31G*(ChelpG). As our parameterization is targeted to reproduce thermal properties of the thermoplastic polyimides, the choice of proper partial charges was finalized on a basis of the closest match between computational and experimental data for the thermal expansion coefficients of the polyimides below glass transition temperatures. Our finding clearly show that the best agreement with experimental data is achieved with the Mulliken partial atomic charges calculated by the Hartree‐Fock method with 6–31G* basis set. Furthermore, in addition to the thermal expansion coefficients this set of partial atomic charges predicts an experimentally observed relationship between glass transition temperatures of the three polyimides under study: . A mechanism behind the change in thermal properties upon the change in the chemical structure in considered polyimides may be related to an additional spatial ordering of sulfone groups due to dipole‐dipole interactions. Overall, the modified force‐field is proved to be suitable for accurate prediction of thermal properties of thermoplastic polyimides and can serve as a basis for building up atomistic theoretical models for describing other heterocyclic polymers in bulk. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 912–923 相似文献
6.
7.
O.M. Lyulin E.V. Karlovets D. Jacquemart Y. Lu A.W. Liu V.I. Perevalov 《Journal of Quantitative Spectroscopy & Radiative Transfer》2012,113(17):2167-2181
The assignment of the high resolution Fourier transform spectra of carbon dioxide enriched in 17O and 18O which were recorded in LADIR (Paris, France) with the Bruker IFS 125-HR between 1800 and 9000 cm?1 and in USTC (Hefei, China) with the Bruker IFS 120-HR between 1700 and 9000 cm?1 was performed. In total 239 bands of 12 isotopologues: 16O12C16O, 16O12C18O, 16O13C16O, 16O13C18O, 18O12C18O, 18O13C18O, 16O12C17O, 17O12C17O, 17O12C18O, 16O13C17O, 17O13C17O and 17O13C18O were observed. Among them, 99 bands were observed for the first time. The majority of new observed bands belong to 17OCO isotopologues. The positions of 23,003 lines were determined with the experimental uncertainty on the level of 0.001 cm?1. The spectroscopic constants were fitted to the observed line positions for all observed bands. 相似文献
8.
Alexey V. Lyulin J. Li Tim Mulder Bart Vorselaars M.A.J. Michels 《Macromolecular Symposia》2006,237(1):108-118
Summary: In order to have better insight into the polymer specifics of the dynamic glass transition molecular dynamics (MD) computer simulations of three glass-formers have been carried out: low-molecular-weight isopropylbenzene (iPB), brittle atactic polystyrene (PS) and tough bisphenol A polycarbonate (PC). Simulation of the uniaxial deformation of these mechanically different types of amorphous polymers shows that the mechanical experimental data could be realistically reproduced. Now the objective is to study the local orientational mobility in the non-deformed isotropic state and to find the possible connection of the segmental dynamics with the different bulk mechanical properties. Local orientational mobility has been studied via Legendre polynomials of the second order and CONTIN analysis. Insight into local orientational dynamics on a range of length- and time scales is acquired. The fast transient ballistic process describing the very initial part of the relaxation has been observed for all temperatures. For all three simulated materials the slowing down of cage escape (α-relaxation) follows mode-coupling theory above Tg, with non-universal, material-specific exponents. Below Tg universal activated segmental motion has been found. At high temperature the α process is merged with the β process. The β process which corresponds to the motions within cage continues below Tg and can be described by an activation law. 相似文献
9.
The characteristics of local motion are explored by molecular dynamics simulations in a series of AB(2)-type dendrimer melts. Systems of generations 3-5 were simulated in a wide temperature range, allowing the assessment of effects associated with molecular size, proximity to the detected glasslike transitions, and the strong connectivity constraints imposed by the dendritic topology. Investigation of the mechanisms involved in local motion at short temporal and spatial scales revealed the connection between the non-Gaussian nature of monomer displacements to alpha-relaxation and the caging/decaging process under different degrees of confinement. In the latter mechanism, two characteristic localization lengths were identified: at the low temperature limit spatial localization was realized within approximately 10% of the nearest neighbor distance while at temperatures higher than the glass transition, the existence of an analogous length scale is ascribed to the geometric constraints due to the dense connectivity pattern. As the results from this study are discussed in comparison to the behavior observed in linear polymers and supercooled liquids, new insight is provided on the universal/specific mechanisms involved in local dynamics of different glass-forming systems. 相似文献
10.
R Nirmala V Sankaranarayanan K Sethupathi AV Morozkin T Geethakumary Y Hariharan 《Pramana》2002,58(5-6):1101-1104
New R
2Ti3Ge4 (R=Dy, Ho and Er) intermetallic compounds have been synthesized and characterized by X-ray diffraction and low temperature ac
magnetic susceptibility, electrical resistivity and thermoelectric power measurements were carried out. The compounds crystallize
in the parent, Sm5Ge4-type orthorhombic structure (space group Pnma) and lanthanide contraction is observed as one moves along the rare-earth series.
The changeover from paramagnetic to antiferromagnetic phase happens at low temperatures and the ordering temperature scales
with the de Gennes factor. The electrical resistivity is metallic with a negative curvature above 100 K. Thermopower displays
a weak maximum at temperatures less than 50 K signifying the possible phonon and magnon drag effects. 相似文献