22 research outputs found
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) 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