scholarly journals Crystal, Fivefold and Glass Formation in Clusters of Polymers Interacting with the Square Well Potential

Polymers ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1111
Author(s):  
Miguel Herranz ◽  
Manuel Santiago ◽  
Katerina Foteinopoulou ◽  
Nikos Ch. Karayiannis ◽  
Manuel Laso
Keyword(s):  
Local Density ◽  
Hard Spheres ◽  
Local Environment ◽  
Crystal Nucleation ◽  
Average Chain Length ◽  
Model Parameters ◽  
Face Centered Cubic ◽  
Polymer Systems ◽  
Hexagonal Close Packed ◽  
Square Well

We present results, from Monte Carlo (MC) simulations, on polymer systems of freely jointed chains with spherical monomers interacting through the square well potential. Starting from athermal packings of chains of tangent hard spheres, we activate the square well potential under constant volume and temperature corresponding effectively to instantaneous quenching. We investigate how the intensity and range of pair-wise interactions affected the final morphologies by fixing polymer characteristics such as average chain length and tolerance in bond gaps. Due to attraction chains are brought closer together and they form clusters with distinct morphologies. A wide variety of structures is obtained as the model parameters are systematically varied: weak interactions lead to purely amorphous clusters followed by well-ordered ones. The latter include the whole spectrum of crystal morphologies: from virtually perfect hexagonal close packed (HCP) and face centered cubic (FCC) crystals, to random hexagonal close packed layers of single stacking direction of alternating HCP and FCC layers, to structures of mixed HCP/FCC character with multiple stacking directions and defects in the form of twins. Once critical values of interaction are met, fivefold-rich glassy clusters are formed. We discuss the similarities and differences between energy-driven crystal nucleation in thermal polymer systems as opposed to entropy-driven phase transition in athermal polymer packings. We further calculate the local density of each site, its dependence on the distance from the center of the cluster and its correlation with the crystallographic characteristics of the local environment. The short- and long-range conformations of chains are analyzed as a function of the established cluster morphologies.

scholarly journals Self-Avoiding Random Walks as a Model to Study Athermal Linear Polymers under Extreme Plate Confinement

Polymers ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 799
Author(s):  
Oscar Parreño ◽  
Pablo Miguel Ramos ◽  
Nikos Ch. Karayiannis ◽  
Manuel Laso
Keyword(s):  
Random Walks ◽  
Hard Spheres ◽  
Configurational Entropy ◽  
Polymer Chains ◽  
Crystal Nucleation ◽  
Face Centered Cubic ◽  
Linear Polymers ◽  
Parallel Plates ◽  
Uniform Size ◽  
Chain Conformations

Monte Carlo (MC) simulations, built around chain-connectivity-altering moves and a wall-displacement algorithm, allow us to simulate freely-jointed chains of tangent hard spheres of uniform size under extreme confinement. The latter is realized through the presence of two impenetrable, flat, and parallel plates. Extreme conditions correspond to the case where the distance between the plates approaches the monomer size. An analysis of the local structure, based on the characteristic crystallographic element (CCE) norm, detects crystal nucleation and growth at packing densities well below the ones observed in bulk analogs. In a second step, we map the confined polymer chains into self-avoiding random walks (SAWs) on restricted lattices. We study all realizations of the cubic crystal system: simple, body centered, and face centered cubic crystals. For a given chain size (SAW length), lattice type, origin of SAW, and level of confinement, we enumerate all possible SAWs (equivalently all chain conformations) and calculate the size distribution. Results for intermediate SAW lengths are used to predict the behavior of long, fully entangled chains through growth formulas. The SAW analysis will allow us to determine the corresponding configurational entropy, as it is the driving force for the observed phase transition and the determining factor for the thermodynamic stability of the corresponding crystal morphologies.

scholarly journals Entropy-Driven Heterogeneous Crystallization of Hard-Sphere Chains under Unidimensional Confinement

Polymers ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1352
Author(s):  
Pablo Miguel Ramos ◽  
Miguel Herranz ◽  
Katerina Foteinopoulou ◽  
Nikos Ch. Karayiannis ◽  
Manuel Laso
Keyword(s):  
Phase Transition ◽  
Volume Fraction ◽  
Hard Spheres ◽  
Local Symmetry ◽  
Crystal Nucleation ◽  
Surface Crystallization ◽  
Face Centered Cubic ◽  
Bulk Crystallization ◽  
Wide Range ◽  
Heterogeneous Crystallization

We investigate, through Monte Carlo simulations, the heterogeneous crystallization of linear chains of tangent hard spheres under confinement in one dimension. Confinement is realized through flat, impenetrable, and parallel walls. A wide range of systems is studied with respect to their average chain lengths (N = 12 to 100) and packing densities (ϕ = 0.50 to 0.61). The local structure is quantified through the Characteristic Crystallographic Element (CCE) norm descriptor. Here, we split the phenomenon into the bulk crystallization, far from the walls, and the projected surface crystallization in layers adjacent to the confining surfaces. Once a critical volume fraction is met, the chains show a phase transition, starting from regions near the hard walls. The established crystal morphologies consist of alternating hexagonal close-packed or face-centered cubic layers with a stacking direction perpendicular to the confining walls. Crystal layer perfection is observed with an increasing concentration. As in the case of the unconstrained phase transition of athermal polymers at high densities, crystal nucleation and growth compete with the formation of sites of a fivefold local symmetry. While surface crystallites show perfection with a predominantly triangular character, the morphologies of square crystals or of a mixed type are also formed. The simulation results show that the rate of perfection of the surface crystallization is not significantly faster than that of the bulk crystallization.

scholarly journals Stability and equation of state of face-centered cubic and hexagonal close packed phases of argon under pressure

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Agnès Dewaele ◽  
Angelika D. Rosa ◽  
Nicolas Guignot ◽  
Denis Andrault ◽  
João Elias F. S. Rodrigues ◽  
...  
Keyword(s):  
Equation Of State ◽  
Single Crystal ◽  
Single Crystal Sample ◽  
Moderate Pressure ◽  
Face Centered Cubic ◽  
Experimental Conditions ◽  
Crystal Sample ◽  
Hexagonal Close Packed ◽  
Face Centered ◽  
Fcc Phase

AbstractThe compression of argon is measured between 10 K and 296 K up to 20 GPa and and up to 114 GPa at 296 K in diamond anvil cells. Three samples conditioning are used: (1) single crystal sample directly compressed between the anvils, (2) powder sample directly compressed between the anvils, (3) single crystal sample compressed in a pressure medium. A partial transformation of the face-centered cubic (fcc) phase to a hexagonal close-packed (hcp) structure is observed above 4.2–13 GPa. Hcp phase forms through stacking faults in fcc-Ar and its amount depends on pressurizing conditions and starting fcc-Ar microstructure. The quasi-hydrostatic equation of state of the fcc phase is well described by a quasi-harmonic Mie–Grüneisen–Debye formalism, with the following 0 K parameters for Rydberg-Vinet equation: $$V_0$$ V 0 = 38.0 Å$$^3$$ 3 /at, $$K_0$$ K 0 = 2.65 GPa, $$K'_0$$ K 0 ′ = 7.423. Under the current experimental conditions, non-hydrostaticity affects measured P–V points mostly at moderate pressure ($$\le$$ ≤ 20 GPa).

scholarly journals Microstructure Refinement by Low-Temperature Ausforming in an Fe-Based Metastable High-Entropy Alloy

Metals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 742
Author(s):  
Motomichi Koyama ◽  
Takeaki Gondo ◽  
Kaneaki Tsuzaki
Keyword(s):  
Low Temperature ◽  
Plastic Anisotropy ◽  
High Entropy Alloy ◽  
Face Centered Cubic ◽  
High Entropy ◽  
Microstructure Refinement ◽  
Hexagonal Close Packed ◽  
Solution Treated Condition ◽  
Solution Treated ◽  
Face Centered

The effects of ausforming in an Fe30Mn10Cr10Co high-entropy alloy on the microstructure, hardness, and plastic anisotropy were investigated. The alloy showed a dual-phase microstructure consisting of face-centered cubic (FCC) austenite and hexagonal close-packed (HCP) martensite in the as-solution-treated condition, and the finish temperature for the reverse transformation was below 200 °C. Therefore, low-temperature ausforming at 200 °C was achieved, which resulted in microstructure refinement and significantly increased the hardness. Furthermore, plasticity anisotropy, a common problem in HCP structures, was suppressed by the ausforming treatment. This, in turn, reduced the scatter of the hardness.

Observation of the Formation Processes of Hexagonal Close-packed and Face-centered Cubic Ru Nanoparticles

2019 ◽  
Vol 48 (9) ◽  
pp. 1062-1064 ◽  
Author(s):  
Naoki Araki ◽  
Kohei Kusada ◽  
Satoru Yoshioka ◽  
Takeharu Sugiyama ◽  
Toshiaki Ina ◽  
...  
Keyword(s):  
Face Centered Cubic ◽  
Formation Processes ◽  
Hexagonal Close Packed ◽  
Ru Nanoparticles ◽  
Face Centered

Stars and stripes. Nanoscale misfit dislocation patterns on surfaces

2002 ◽  
Vol 74 (9) ◽  
pp. 1663-1671 ◽  
Author(s):  
Raghani Pushpa ◽  
Shobhana Narasimhan
Keyword(s):  
Surface Structure ◽  
Misfit Dislocation ◽  
Domain Walls ◽  
Chemical Potential ◽  
Model System ◽  
Misfit Dislocations ◽  
Face Centered Cubic ◽  
Hexagonal Close Packed ◽  
Structure Changes ◽  
Face Centered

Close-packed metal surfaces and heteroepitaxial systems frequently display a structure consisting of regularly spaced misfit dislocations, with a network of domain walls separating face-centered cubic (fcc) and hexagonal close-packed (hcp) domains. These structures can serve as templates for growing regularly spaced arrays of nanoislands. We present a theoretical investigation of the factors controlling the size and shape of the domains, using Pt(111) as a model system. Upon varying the chemical potential, the surface structure changes from being unreconstructed to the honeycomb, wavy triangles, "bright stars", or Moiré patterns observed experimentally on Pt(111) and other systems. For the particular case of Pt(111), isotropically contracted star-like patterns are favored over uniaxially contracted stripes.

Equilibrium Structure and Schottky Barriers at Eras/Gaas Interfaces

1997 ◽  
Vol 492 ◽  
Author(s):  
A. G. Petukhov ◽  
B. T. Hemmelman ◽  
W. R. L. Lambrecht
Keyword(s):  
Local Density ◽  
Equilibrium Structure ◽  
Schottky Barriers ◽  
Orbital Method ◽  
Full Potential ◽  
Face Centered Cubic ◽  
Erbium Arsenide ◽  
Self Energy ◽  
Ideal Situation ◽  
Face Centered

ABSTRACTThe equilibrium structures as well as the electronic Schottky barriers for (100) Erbium-Arsenide/Gallium-Arsenide (ErAs/GaAs) arsenic and gallium terminated interfaces have been determined by ab-initio calculations using the local-density approximation and a full-potential linear-muffin-tin-orbital method. In both cases the arsenic sublattice was chosen to be continuous across the interface in accordance with experiments on Rutherford backscattering channeling. Band structures, densities of states, and charge density distributions were also determined for the interfaces. The comparison of the total supercell energies reveals that the gallium terminated (chain) interface is more energetically stable than the arsenic terminated (shadow) interface. It also shows that the equilibrium interface separation for the arsenic terminated interface corresponds to an ideal structure when arsenic forms undistorted face-centered cubic lattice. The separation in the gallium terminated interface is quite substantial and is 60% larger than that of the ideal situation. The model also predicts that no buckling of the ErAs interface monolayer will occur for either structure. The computed Schottky barriers for holes (after a semi-empirical quasiparticle self-energy correction) are 0.6 eV for the chain interface and 0.4 eV for the shadow interface.

scholarly journals Свойства движущихся дискретных бризеров в бериллии

2018 ◽  
Vol 60 (5) ◽  
pp. 978
Author(s):  
O.B. Бачурина ◽  
P.T. Мурзаев ◽  
A.C. Семенов ◽  
E.A. Корзникова ◽  
C.B. Дмитриев
Keyword(s):  
Energy Transport ◽  
Interatomic Potential ◽  
Maximum Velocity ◽  
Face Centered Cubic ◽  
Sound Waves ◽  
Many Body ◽  
Hexagonal Close Packed ◽  
Bcc Lattice ◽  
Face Centered ◽  
The Many

AbstractDiscrete breathers (DBs) have been described among pure metals with face-centered cubic (FCC) and body-centered cubic (BCC) lattice, but for hexagonal close-packed (HCP) metals, their properties are little studied. In this paper, the properties of standing and moving DBs in beryllium HCP metal are analyzed by the molecular dynamics method using the many-body interatomic potential. It is shown that the DB is localized in a close-packed atomic row in the basal plane, while oscillations with a large amplitude along the close-packed row are made by two or three atoms, moving in antiphase with the nearest neighbors. Dependences of the DB frequency on the amplitude, as well as the velocity of the DB on its amplitude and on parameter δ, which determines the phase difference of the oscillations of neighboring atoms, are obtained. The maximum velocity of the DB movement in beryllium reaches 4.35 km/s, which is 33.7% of the velocity of longitudinal sound waves. The obtained results supplement our concepts about the mechanisms of localization and energy transport in HCP metals.

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