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 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 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.

Normal stresses in concentrated non-Brownian suspensions

2013 ◽  
Vol 715 ◽  
pp. 239-272 ◽  
Author(s):  
T. Dbouk ◽  
L. Lobry ◽  
E. Lemaire
Keyword(s):  
Normal Stress ◽  
Pore Pressure ◽  
Volume Fraction ◽  
Hard Spheres ◽  
Particle Volume Fraction ◽  
Radial Profile ◽  
Normal Stresses ◽  
Particle Volume ◽  
Wide Range ◽  
Normal Stress Differences

AbstractWe present an experimental approach used to measure both normal stress differences and the particle phase contribution to the normal stresses in suspensions of non-Brownian hard spheres. The methodology consists of measuring the radial profile of the normal stress along the velocity gradient direction in a torsional flow between two parallel discs. The values of the first and the second normal stress differences, ${N}_{1} $ and ${N}_{2} $, are deduced from the measurement of the slope and of the origin ordinate. The measurements are carried out for a wide range of particle volume fractions (between 0.2 and 0.5). As expected, ${N}_{2} $ is measured to be negative but ${N}_{1} $ is found to be positive. We discuss the validity of the method and present numerous tests that have been carried out in order to validate our results. The experimental setup also allows the pore pressure to be measured. Then, subtracting the pore pressure from the total stress, ${\mbrm{\Sigma} }_{\mathbf{22} } $, the contribution of the particles to the normal stress ${ \mbrm{\Sigma} }_{\mathbf{22} }^{\mathbi{p}} $ is obtained. Most of our results compare well with the different experimental and numerical data present in the literature. In particular, our results show that the magnitude of the particle stress tensor component and their dependence on the particle volume fraction used in the suspension model balance proposed by Morris & Boulay (J. Rheol., vol. 43, 1999, p. 1213) are suitable.

scholarly journals Microstructure, Hardness, and Elastic Modulus of a Multibeam-Sputtered Nanocrystalline Co-Cr-Fe-Ni Compositional Complex Alloy Film

Materials ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3357
Author(s):  
Péter Nagy ◽  
Nadia Rohbeck ◽  
Zoltán Hegedűs ◽  
Johann Michler ◽  
László Pethö ◽  
...  
Keyword(s):  
Elastic Modulus ◽  
Crystallite Size ◽  
Physical Vapor Deposition ◽  
Defect Density ◽  
Lattice Defect ◽  
Chemical Compositions ◽  
Line Profile Analysis ◽  
Face Centered Cubic ◽  
Complex Alloy ◽  
Wide Range

A nanocrystalline Co-Cr-Ni-Fe compositional complex alloy (CCA) film with a thickness of about 1 micron was produced by a multiple-beam-sputtering physical vapor deposition (PVD) technique. The main advantage of this novel method is that it does not require alloy targets, but rather uses commercially pure metal sources. Another benefit of the application of this technique is that it produces compositional gradient samples on a disk surface with a wide range of elemental concentrations, enabling combinatorial analysis of CCA films. In this study, the variation of the phase composition, the microstructure (crystallite size and defect density), and the mechanical performance (hardness and elastic modulus) as a function of the chemical composition was studied in a combinatorial Co-Cr-Ni-Fe thin film sample that was produced on a surface of a disk with a diameter of about 10 cm. The spatial variation of the crystallite size and the density of lattice defects (e.g., dislocations and twin faults) were investigated by X-ray diffraction line profile analysis performed on the patterns taken by synchrotron radiation. The hardness and the elastic modulus were measured by the nanoindentation technique. It was found that a single-phase face-centered cubic (fcc) structure was formed for a wide range of chemical compositions. The microstructure was nanocrystalline with a crystallite size of 10–27 nm and contained a high lattice defect density. The hardness and the elastic modulus values measured for very different compositions were in the ranges of 8.4–11.8 and 182–239 GPa, respectively.

scholarly journals Factors Affecting Acoustic Properties of Natural-Fiber-Based Materials and Composites: A Review

Textiles ◽  
2021 ◽  
Vol 1 (1) ◽  
pp. 55-85
Author(s):  
Tufail Hassan ◽  
Hafsa Jamshaid ◽  
Rajesh Mishra ◽  
Muhammad Qamar Khan ◽  
Michal Petru ◽  
...  
Keyword(s):  
Sound Absorption ◽  
Natural Fiber ◽  
Volume Fraction ◽  
Fiber Type ◽  
Alkali Treatment ◽  
Acoustic Properties ◽  
Synthetic Fiber ◽  
Sound Insulation ◽  
Factors Affecting ◽  
Wide Range

Recently, very rapid growth has been observed in the innovations and use of natural-fiber-based materials and composites for acoustic applications due to their environmentally friendly nature, low cost, and good acoustic absorption capability. However, there are still challenges for researchers to improve the mechanical and acoustic properties of natural fiber composites. In contrast, synthetic fiber-based composites have good mechanical properties and can be used in a wide range of structural and automotive applications. This review aims to provide a short overview of the different factors that affect the acoustic properties of natural-fiber-based materials and composites. The various factors that influence acoustic performance are fiber type, fineness, length, orientation, density, volume fraction in the composite, thickness, level of compression, and design. The details of various factors affecting the acoustic behavior of the fiber-based composites are described. Natural-fiber-based composites exhibit relatively good sound absorption capability due to their porous structure. Surface modification by alkali treatment can enhance the sound absorption performance. These materials can be used in buildings and interiors for efficient sound insulation.

scholarly journals Conduction and convection heat transfer characteristics of water-based au nanofluids in a square cavity with differentially heated side walls subjected to constant temperatures

2014 ◽  
Vol 18 (suppl.1) ◽  
pp. 189-200 ◽  
Author(s):  
Primoz Ternik ◽  
Rebeka Rudolf
Keyword(s):  
Heat Transfer ◽  
Rayleigh Number ◽  
Base Fluid ◽  
Volume Fraction ◽  
Heat Transfer Characteristics ◽  
Square Cavity ◽  
Onset Of Convection ◽  
Transfer Characteristics ◽  
Wide Range ◽  
Water Based

The present work deals with the natural convection in a square cavity filled with the water-based Au nanofluid. The cavity is heated on the vertical and cooled from the adjacent wall, while the other two horizontal walls are adiabatic. The governing differential equations have been solved by the standard finite volume method and the hydrodynamic and thermal fields were coupled together using the Boussinesq approximation. The main objective of this study is to investigate the influence of the nanoparticles? volume fraction on the heat transfer characteristics of Au nanofluids at the given base fluid?s (i.e. water) Rayleigh number. Accurate results are presented over a wide range of the base fluid Rayleigh number and the volume fraction of Au nanoparticles. It is shown that adding nanoparticles in a base fluid delays the onset of convection. Contrary to what is argued by many authors, we show by numerical simulations that the use of nanofluids can reduce the heat transfer rate instead of increasing it.

scholarly journals Microstructure and magnetic properties of Nd-Fe-B-(Re, Ti) alloys

Nukleonika ◽  
2015 ◽  
Vol 60 (1) ◽  
pp. 29-33
Author(s):  
Mariusz Hasiak
Keyword(s):  
Magnetic Properties ◽  
Phase Composition ◽  
Volume Fraction ◽  
Magnetic Characteristics ◽  
Ti Alloys ◽  
Wide Range ◽  
Magnetically Hard ◽  
Ti Addition ◽  
Microstructure And Magnetic Properties

Abstract The microstructure and magnetic properties of nanocomposite hard magnetic Nd-Fe-B-(Re, Ti) materials with different Nd and Fe contents are studied. The role of Re and Ti addition in phase composition and volume fraction of the Nd-Fe-B phase is determined. All samples are annealed at the same temperature of 993 K for 10 min. Mössbauer spectroscopy shows that the addition of 4 at.% of Re to the Nd8Fe78B14 alloy leads to creation of an ineligible amount of the magnetically hard Nd2Fe14B phase. Moreover, the microstructure and magnetic characteristics recorded in a wide range of temperatures for the Nd8Fe79−xB13Mx (x = 4; M = Re or Ti) alloys are also analyzed.

scholarly journals Effects of Polydispersity on the Phase Behavior of Additive Hard Spheres in Solution

Molecules ◽  
2021 ◽  
Vol 26 (6) ◽  
pp. 1543
Author(s):  
Luka Sturtewagen ◽  
Erik van der Linden
Keyword(s):  
Phase Behavior ◽  
Critical Point ◽  
Volume Fraction ◽  
Hard Spheres ◽  
Second Virial Coefficient ◽  
Two Phase ◽  
Different Types ◽  
Asymmetric Partitioning ◽  
Average Size ◽  
Liquid Liquid Phase Separation

The ability to separate enzymes, nucleic acids, cells, and viruses is an important asset in life sciences. This can be realised by using their spontaneous asymmetric partitioning over two macromolecular aqueous phases in equilibrium with one another. Such phases can already form while mixing two different types of macromolecules in water. We investigate the effect of polydispersity of the macromolecules on the two-phase formation. We study theoretically the phase behavior of a model polydisperse system: an asymmetric binary mixture of hard spheres, of which the smaller component is monodisperse and the larger component is polydisperse. The interactions are modelled in terms of the second virial coefficient and are assumed to be additive hard sphere interactions. The polydisperse component is subdivided into sub-components and has an average size ten times the size of the monodisperse component. We calculate the theoretical liquid–liquid phase separation boundary (the binodal), the critical point, and the spinodal. We vary the distribution of the polydisperse component in terms of skewness, modality, polydispersity, and number of sub-components. We compare the phase behavior of the polydisperse mixtures with their concomittant monodisperse mixtures. We find that the largest species in the larger (polydisperse) component causes the largest shift in the position of the phase boundary, critical point, and spinodal compared to the binary monodisperse binary mixtures. The polydisperse component also shows fractionation. The smaller species of the polydisperse component favor the phase enriched in the smaller component. This phase also has a higher-volume fraction compared to the monodisperse mixture.

scholarly journals Eccentricity based topological indices of face centered cubic lattice FCC(n)

2020 ◽  
Vol 44 (1) ◽  
pp. 32-38
Author(s):  
Hani Shaker ◽  
Muhammad Imran ◽  
Wasim Sajjad
Keyword(s):  
Wiener Index ◽  
Face Centered Cubic ◽  
Eccentric Connectivity Index ◽  
Zagreb Index ◽  
Cubic Lattice ◽  
Chemical Graph ◽  
Chemical Graph Theory ◽  
Wide Range ◽  
Unit Cells ◽  
Face Centered

Abstract Chemical graph theory has become a prime gadget for mathematical chemistry due to its wide range of graph theoretical applications for solving molecular problems. A numerical quantity is named as topological index which explains the topological characteristics of a chemical graph. Recently face centered cubic lattice FCC(n) attracted large attention due to its prominent and distinguished properties. Mujahed and Nagy (2016, 2018) calculated the precise expression for Wiener index and hyper-Wiener index on rows of unit cells of FCC(n). In this paper, we present the ECI (eccentric-connectivity index), TCI (total-eccentricity index), CEI (connective eccentric index), and first eccentric Zagreb index of face centered cubic lattice.

Laser-Induced Pretransitional Ordering And Nonlinear Optical Properties Of Rigid-Rod Polymer Suspensions

1993 ◽  
Vol 328 ◽  
Author(s):  
Boris E. Vugmeister ◽  
Michelle S. Malcuit ◽  
John C. Kralik ◽  
Colleen Stevens
Keyword(s):  
Phase Transition ◽  
Colloidal Particles ◽  
Volume Fraction ◽  
Orientational Order ◽  
Critical Value ◽  
Orientational Relaxation ◽  
First Order ◽  
First Order Phase Transition ◽  
Rigid Rod ◽  
First Order Phase

ABSTRACTWe investigate the pretransitional behavior in laser-induced alignment of rigid rod-like polytetraflouroethylene (PTFE) suspensions. Using a laser-induced birefringence experiment, we measure both the orientational order parameter and the orientational relaxation time. We find that both increase as the volume fraction of colloidal particles approaches the critical value for the isotropic-nematic phase transition. Experimental results are compared with theory which takes into account the possibility of a first-order phase transition induced by a laser electric field.

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