Conformational and Structural Relaxations of Poly(ethylene oxide) and Poly(propylene oxide) Melts: Molecular Dynamics Study of Spatial Heterogeneity, Cooperativity, and Correlated Forward-Backward Motion

Performing molecular dynamics simulations for all-atom models, we characterize the conformational and structural relaxations of poly(ethylene oxide) and poly(propylene oxide) melts. The temperature dependence of these relaxation processes deviates from an Arrhenius law for both polymers. We demonstrate that mode-coupling theory captures some aspects of the glassy slowdown, but it does not enable a complete explanation of the dynamical behavior. When the temperature is decreased, spatially heterogeneous and cooperative translational dynamics are found to become more important for the structural relaxation. Moreover, the transitions between the conformational states cease to obey Poisson statistics. In particular, we show that, at sufficiently low temperatures, correlated forward-backward motion is an important aspect of the conformational relaxation, leading to strongly nonexponential distributions for the waiting times of the dihedrals in the various conformational statesComment: 13 pages, 13 figure

Computersimulationen zur Dynamik und Statik von Polybutadienschmelzen

In this thesis the dynamics and static behavior of polybutadiene melts are studied by computer simulations. From the content: Microstructure of polybutadiene. Comparison of computer models. Particle interactions. Thermodynamics of polymer melts. Dynamics and static behavior of single chains. Dynamics of dense polymer melts.SIGLEAvailable from: http://ArchiMeD.uni-mainz.de/pub/2002/0113/diss.pdf / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

ДОСЛІДЖЕННЯ ЗЦІПНИХ ВЛАСТИВОСТЕЙ ВАГОНУ ЕЛЕКТРОПОТЯГА НА ЧОТИРЬОХ ОДНОВІСНИХ ВІЗКАХ

In given article are considered processes, appearing in tractive электроприводе motor coach электропоезда on four одноосных pushcart at failure of the traction. Also happen to the frequencies of the fluctuations this drive element both before, and after failure of the traction.Рассматриваются процессы, возникающие в тяговом электроприводе моторного вагона электропоезда на четырёх одноосных тележках при срыве сцепления. Также приводятся частоты колебаний элементов этого привода до и после срыва сцепления.Розглядаються процеси, що виникають у тяговому електроприводі моторного вагона електропоїзда на чотирьох одноосьових візках при зриві зчеплення. Також наводяться частоти коливань елементів цього привода до і після зриву зчеплення

Dipolar Correlations in 1,4-Polybutadiene Across the Timescales : a Numerical Molecular Dynamics Simulation Investigation

Research Program SPP 1369 (German Science Foundation)International audienceBroadband dielectric spectroscopy is able to follow the time correlation of its observable, the polarization of a sample, over an unprecedented range of frequency or timescales, respectively. Features in the dielectric susceptibility as a function of frequency are assigned to different molecular motions, which, for polymers in the melt, range from high-frequency vibrations over a possible Johari-Goldstein β-relaxation, the segmental or α-relaxation, a possible normal mode for chains with a net dipole moment along the end-to-end vector of the chain to conductivity contributions on the low-frequency side. This assignment is a statement about correlations between the local dipole moments making up the sample polarization and their behavior across length and timescales. Such correlations can depend on temperature and on density as well as on confinement effects. A molecular dynamics simulation of a chemically realistic model of 1,4-polybutadiene confined between graphite walls allows for a study of such correlations over a broad temperature range in the bulk-like center of the film, as well as in the wall regions where confinement -induced correlations are present. We have already shown that confinement induces a new type of normal mode into this polymer which does not possess such a mode in the bulk. Here, we discuss the scaling of the dielectric relaxation process in this system and additionally analyze the temperature and confinement dependence of high-frequency vibrations