Static Rouse Modes and Related Quantities: Corrections to Chain Ideality in Polymer Melts

Following the Flory ideality hypothesis intrachain and interchain excluded volume interactions are supposed to compensate each other in dense polymer systems. Multi-chain effects should thus be neglected and polymer conformations may be understood from simple phantom chain models. Here we provide evidence against this phantom chain, mean-field picture. We analyze numerically and theoretically the static correlation function of the Rouse modes. Our numerical results are obtained from computer simulations of two coarse-grained polymer models for which the strength of the monomer repulsion can be varied, from full excluded volume (`hard monomers') to no excluded volume (`phantom chains'). For nonvanishing excluded volume we find the simulated correlation function of the Rouse modes to deviate markedly from the predictions of phantom chain models. This demonstrates that there are nonnegligible correlations along the chains in a melt. These correlations can be taken into account by perturbation theory. Our simulation results are in good agreement with these new theoretical predictions.Comment: 9 pages, 7 figures, accepted for publication in EPJ

Understanding Segmental Dynamics in Polymer Electrolytes: A Computer Study

We study the segmental dynamics of poly(ethylene oxide) (PEO) from microscopic simulations in the neat polymer and a polymer electrolyte (PEO/LiBF$_4$) by analyzing the normal modes. We verify the applicability of the Rouse theory, specifically for the polymer electrolyte where dynamic heterogeneities, arising from cation-polymer interactions, alter the mobility non-uniformly along the chains. We find that the Rouse modes for both the systems are orthogonal despite the presence of non-exponential relaxation of the modes and violation of the Gaussian self-similarity of the chains. The slowdown of the segmental dynamics in the polymer electrolyte is rationalised by an order of magnitude increase in the friction coefficient for those monomers which are bound by cations. In general, for the electrolyte the Rouse predictions for the dynamics of segments (both free and/or bound) agree well except for very short times

Molecular dynamics simulations of glassy polymers

We review recent results from computer simulation studies of polymer glasses, from chain dynamics around the glass transition temperature Tg to the mechanical behaviour below Tg. These results clearly show that modern computer simulations are able to address and give clear answers to some important issues in the field, in spite of the obvious limitations in terms of length and time scales. In the present review we discuss the cooling rate effects, and dynamic slowing down of different relaxation processes when approaching Tg for both model and chemistry-specific polymer glasses. The impact of geometric confinement on the glass transition is discussed in detail. We also show that computer simulations are very useful tools to study structure and mechanical response of glassy polymers. The influence of large deformations on mechanical behaviour of polymer glasses in general, and strain hardening effect in particular are reviewed. Finally, we suggest some directions for future research, which we believe will be soon within the capabilities of state of the art computer simulations, and correspond to problems of fundamental interest.Comment: To apear in "Soft Matter

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

Direct numerical simulation of flexible molecules and data-driven molecular conformation

The present work aims at performing a molecular dynamics modeling of suspensions composed of flexible linear molecules. Molecules are represented by a series of connected beads, whose dynamics is governed by three potentials: the extension potential affecting the elongation of segments connecting consecutive beads, the one governing the molecule bending and finally the Lennard-Jones describing the interaction of non-consecutive beads. A population of non-interacting molecules is simulated in elongation and shear flows for different flow and molecule parameters. The flow-induced conformation is analyzed in the different considered situations. Finally a model for predicting the evolution of the population conformation will be obtained by using deep-learning