scholarly journals Open and Anisotropic Soft Regions in a Model Polymer Glass

Polymers ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1336
Author(s):  
Carlo Andrea Massa ◽  
Francesco Puosi ◽  
Antonio Tripodo ◽  
Dino Leporini
Keyword(s):  
Finite Size ◽  
Single Chain ◽  
Finite Size Effects ◽  
Limited Size ◽  
Polymer Glass ◽  
High Participation ◽  
Largest Eigenvalues ◽  
Dynamics Simulations ◽  
Thermodynamic Anomalies ◽  
Single Cluster

The vibrational dynamics of a model polymer glass is studied by Molecular Dynamics simulations. The focus is on the “soft” monomers with high participation to the lower-frequency vibrational modes contributing to the thermodynamic anomalies of glasses. To better evidence their role, the threshold to qualify monomers as soft is made severe, allowing for the use of systems with limited size. A marked tendency of soft monomers to form quasi-local clusters involving up to 15 monomers is evidenced. Each chain contributes to a cluster up to about three monomers and a single cluster involves a monomer belonging to about 2–3 chains. Clusters with monomers belonging to a single chain are rare. The open and tenuous character of the clusters is revealed by their fractal dimension df<2. The inertia tensor of the soft clusters evidences their strong anisotropy in shape and remarkable linear correlation of the two largest eigenvalues. Owing to the limited size of the system, finite-size effects, as well as dependence of the results on the adopted polymer length, cannot be ruled out.

Frictional Properties of Self-Assembled Alkylsilane Chains on Silica

2001 ◽  
Vol 687 ◽  
Author(s):  
M. Chandross ◽  
B. Park ◽  
M. Stevens ◽  
G.S. Grest
Keyword(s):  
Size Effects ◽  
Finite Size ◽  
Shear Velocity ◽  
Finite Size Effects ◽  
Silica Surfaces ◽  
Frictional Properties ◽  
Covalently Bonded ◽  
Comparable Effect ◽  
System Data ◽  
Dynamics Simulations

AbstractWe present the results of molecular dynamics simulations of pairs of alkylsilane monolayers on silica surfaces under shear. In particular, we investigate the effects of shear velocity on the friction for chains of 6, 8, 12, and 18 carbon atoms covalently bonded to a crystalline surface. Our studies are performed at loads close to 0.2 and 2 GPa for relative velocities of 0.2, 2.0, and 20.0 m/s. We find that for perfect (defect-free) monolayers, the effects of chain length and velocity are weak, indicating that the experimentally measured dependence of friction on these properties is primarily due to defects in the monolayer. We have investigated possible finite size effects by varying our system dimensions from 43 Å ×50 Å Å to 174 Å × 201 Å. We find that increasing the surface area by a factor of N reduces the noise in the shear stress by a factor of , and has a comparable effect to averaging the smaller system data over bins of points. This indicates that finite size effects are negligible in our simulations.

Free Volume and Finite-Size Effects in a Polymer Glass under Stress

2007 ◽  
Vol 99 (21) ◽  
Author(s):  
Robert A. Riggleman ◽  
Hau-Nan Lee ◽  
M. D. Ediger ◽  
Juan J. de Pablo
Keyword(s):  
Free Volume ◽  
Size Effects ◽  
Finite Size ◽  
Finite Size Effects ◽  
Polymer Glass

scholarly journals Molecular-dynamics simulations of urea nucleation from aqueous solution

2014 ◽  
Vol 112 (1) ◽  
pp. E6-E14 ◽  
Author(s):  
Matteo Salvalaglio ◽  
Claudio Perego ◽  
Federico Giberti ◽  
Marco Mazzotti ◽  
Michele Parrinello
Keyword(s):  
Aqueous Solution ◽  
Free Energy ◽  
Molecular Simulations ◽  
Finite Size ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Science And Engineering ◽  
Finite Size Effects ◽  
Dynamics Simulations ◽  
Insight Into

Despite its ubiquitous character and relevance in many branches of science and engineering, nucleation from solution remains elusive. In this framework, molecular simulations represent a powerful tool to provide insight into nucleation at the molecular scale. In this work, we combine theory and molecular simulations to describe urea nucleation from aqueous solution. Taking advantage of well-tempered metadynamics, we compute the free-energy change associated to the phase transition. We find that such a free-energy profile is characterized by significant finite-size effects that can, however, be accounted for. The description of the nucleation process emerging from our analysis differs from classical nucleation theory. Nucleation of crystal-like clusters is in fact preceded by large concentration fluctuations, indicating a predominant two-step process, whereby embryonic crystal nuclei emerge from dense, disordered urea clusters. Furthermore, in the early stages of nucleation, two different polymorphs are seen to compete.

scholarly journals Lattice induced crystallization of nanodroplets: the role of finite-size effects and substrate properties in controlling polymorphism

Nanoscale ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 4921-4926 ◽  
Author(s):  
Julien Lam ◽  
James F. Lutsko
Keyword(s):  
Molecular Dynamics ◽  
Size Effects ◽  
Finite Size ◽  
Solid Substrate ◽  
General Phenomenon ◽  
Finite Size Effects ◽  
Substrate Properties ◽  
Dynamics Simulations ◽  
Induced Crystallization

Freezing a nanodroplet deposited on a solid substrate leads to the formation of crystalline structures. We study the inherent mechanisms underlying this general phenomenon by means of molecular dynamics simulations.

Finite-size effects on the static properties of a single-chain magnet

2005 ◽  
Vol 72 (6) ◽  
Author(s):  
L. Bogani ◽  
R. Sessoli ◽  
M. G. Pini ◽  
A. Rettori ◽  
M. A. Novak ◽  
...  
Keyword(s):  
Size Effects ◽  
Finite Size ◽  
Single Chain ◽  
Static Properties ◽  
Finite Size Effects

scholarly journals Patterns and Long Range Correlations in Idealized Granular Flows

1997 ◽  
Vol 08 (04) ◽  
pp. 953-965 ◽  
Author(s):  
J. A. G. Orza ◽  
R. Brito ◽  
T. P. C. van Noije ◽  
M. H. Ernst
Keyword(s):  
Long Range ◽  
Size Effects ◽  
Hard Spheres ◽  
Finite Size ◽  
System Size ◽  
Spatial Correlations ◽  
Finite Size Effects ◽  
Long Range Correlations ◽  
Intrinsic Length ◽  
Dynamics Simulations

An initially homogeneous freely evolving fluid of inelastic hard spheres develops inhomogeneities in the flow field u(r, t) (vortices) and in the density field n (r, t)(clusters), driven by unstable fluctuations, δa = {δn, δu}. Their spatial correlations, <δa(r, t)δa(r′,t)>, as measured in molecular dynamics simulations, exhibit long range correlations; the mean vortex diameter grows as [Formula: see text]; there occur transitions to macroscopic shearing states, etc. The Cahn–Hilliard theory of spinodal decomposition offers a qualitative understanding and quantitative estimates of the observed phenomena. When intrinsic length scales are of the order of the system size, effects of physical boundaries and periodic boundaries (finite size effects in simulations) are important.

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