scholarly journals Multistep nucleation of anisotropic molecules

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Kazuaki Z. Takahashi ◽  
Takeshi Aoyagi ◽  
Jun-ichi Fukuda
Keyword(s):  
Phase Transition ◽  
Materials Science ◽  
Orientational Order ◽  
Functional Materials ◽  
Numerical Approach ◽  
Anisotropic Materials ◽  
Nucleation Theory ◽  
Dynamics Simulation ◽  
Molecular Cluster ◽  
Classical Nucleation Theory

AbstractPhase transition of anisotropic materials is ubiquitously observed in physics, biology, materials science, and engineering. Nevertheless, how anisotropy of constituent molecules affects the phase transition dynamics is still poorly understood. Here we investigate numerically the phase transition of a simple model system composed of anisotropic molecules, and report on our discovery of multistep nucleation of nuclei with layered positional ordering (smectic ordering), from a fluid-like nematic phase with orientational order only (no positional order). A trinity of molecular dynamics simulation, machine learning, and molecular cluster analysis yielding free energy landscapes unambiguously demonstrates the dynamics of multistep nucleation process involving characteristic metastable clusters that precede supercritical smectic nuclei and cannot be accounted for by the classical nucleation theory. Our work suggests that molecules of simple shape can exhibit rich and complex nucleation processes, and our numerical approach will provide deeper understanding of phase transitions and resulting structures in anisotropic materials such as biological systems and functional materials.

A study to investigate phase transitions and nucleation kinetics of nickel and copper

2016 ◽  
Vol 30 (11) ◽  
pp. 1650129 ◽  
Author(s):  
F. A. Celik ◽  
A. K. Yildiz
Keyword(s):  
Molecular Dynamics ◽  
Orientational Order ◽  
Nucleation Theory ◽  
Dynamics Simulation ◽  
Classical Nucleation Theory ◽  
Structural Development ◽  
Nucleation Kinetics ◽  
Embedded Atom ◽  
Bond Orientational Order ◽  
Kinetics Of

In this study, we investigate the homogeneous nucleation kinetics of copper and nickel system during cooling process using molecular dynamics simulation (MDS). The calculation is carried out for a different number of atoms consisting of 500, 2048, 8788 and 13,500 based on embedded atom method (EAM). It is observed that the melting points for the both model increases with increasing the size of systems (i.e. the number of atoms) as expected from Parrinello and Rahman MD method. The interfacial free energies and critical nucleus radius of nickel and copper are also determined by molecular dynamics, and the results are consistent with the classical nucleation theory. The structural development and phase transformation are also determined from the radial distribution function (RDF) and local bond orientational order parameters (LBOO).

Molecular Dynamics Simulation of Nano Cluster-Seed Effects on Heterogeneous Nucleation

2009 ◽  
Author(s):  
Donguk Suh ◽  
Seung-chai Jung ◽  
Woong-sup Yoon
Keyword(s):  
Molecular Dynamics ◽  
Heterogeneous Nucleation ◽  
Three Dimensional ◽  
Seed Mass ◽  
Nucleation Theory ◽  
Dynamics Simulation ◽  
Classical Nucleation Theory ◽  
Supersaturation Ratio ◽  
Order Of Magnitude ◽  
Nano Cluster

A three-dimensional heterogeneous nucleation is simulated by classical molecular dynamics, where the Lennard-Jones gas and solid nano cluster-seed molecules have argon and aluminum properties, respectively. All dimensions of the wall are periodic and a soft core carrier gas within the system controls the temperature rise induced by latent heat of condensation. There are three shapes of cluster-seeds being cube, rod, and sphere, three classes of masses, and the simulation took place under nine supersaturation ratios, making a total of 81 calculations. An analysis of variance was performed under a three-way layout to analyze the cluster-seed and supersaturation ratio effects on the system. For supersaturation ratios above the critical value nucleation rates were evaluated, below growth rates, and overall liquefaction rates were each defined and calculated. Results show that the supersaturation ratio dominantly controls all rates, but seed characteristics are important for the growth of the largest cluster under the critical supersaturation ratio. Overall liquefaction increases subject to an escalation of supersaturation ratio and seed mass. However, the significance of the supersaturation ratio for overall liquefaction suggests that thermal diffusion is more dominant than mass interactions for this system. Homogeneous characteristics are also compared with the heterogeneous system to find that though nucleation may occur for an insufficient supersaturation ratio when a seed is within the system, the addition of a seed does not in fact facilitate the increase in rates of the phenomena at high supersaturation ratios. Finally a comparison with the classical nucleation theory asserts a 3 to 4 order of magnitude difference, which is within the lines of deviation when it comes to theory and molecular simulations.

scholarly journals Hydrate Phase Transition Kinetic Modeling for Nature and Industry–Where Are We and Where Do We Go?

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4149
Author(s):  
Bjørn Kvamme ◽  
Matthew Clarke
Keyword(s):  
Phase Transition ◽  
Natural Gas ◽  
Kinetic Modeling ◽  
Hydrate Formation ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Massive Growth ◽  
Hydrate Phase ◽  
Induction Times ◽  
Classical Thermodynamics

Hydrate problems in industry have historically motivated modeling of hydrates and hydrate phase transition dynamics, and much knowledge has been gained during the last fifty years of research. The interest in natural gas hydrate as energy source is increasing rapidly. Parallel to this, there is also a high focus on fluxes of methane from the oceans. A limited portion of the fluxes of methane comes directly from natural gas hydrates but a much larger portion of the fluxes involves hydrate mounds as a dynamic seal that slows down leakage fluxes. In this work we review some of the historical trends in kinetic modeling of hydrate formation and discussion. We also discuss a possible future development over to classical thermodynamics and residual thermodynamics as a platform for all phases, including water phases. This opens up for consistent thermodynamics in which Gibbs free energy for all phases are comparable in terms of stability, and also consistent calculation of enthalpies and entropies. Examples are used to demonstrate various stability limits and how various routes to hydrate formation lead to different hydrates. A reworked Classical Nucleation Theory (CNT) is utilized to illustrate that nucleation of hydrate is, as expected from physics, a nano-scale process in time and space. Induction times, or time for onset of massive growth, on the other hand, are frequently delayed by hydrate film transport barriers that slow down contact between gas and liquid water. It is actually demonstrated that the reworked CNT model is able to predict experimental induction times.

Molecular Dynamics Based Analysis of Nucleation and Surface Energy of Droplets in Supersaturated Vapors of Methane and Ethane

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Jadran Vrabec ◽  
Martin Horsch ◽  
Hans Hasse
Keyword(s):  
Molecular Dynamics ◽  
Surface Energy ◽  
Droplet Size ◽  
Nucleation Rate ◽  
Homogeneous Nucleation ◽  
First Passage Time ◽  
Nucleation Theory ◽  
Dynamics Simulation ◽  
Classical Nucleation Theory ◽  
Critical Droplet

Homogeneous nucleation processes are characterized by the nucleation rate and the critical droplet size. Molecular dynamics simulation is applied for studying homogeneous nucleation during condensation of supersaturated vapors of methane and ethane. The results are compared with the classical nucleation theory (CNT) and the Laaksonen–Ford–Kulmala (LFK) model that introduces the size dependence of the specific surface energy. It is shown for the nucleation rate that the Yasuoka–Matsumoto method and the mean first passage time method lead to considerably differing results. Even more significant deviations are found between two other approaches to the critical droplet size, based on the maximum of the Gibbs free energy of droplet formation (Yasuoka–Matsumoto) and the supersaturation dependence of the nucleation rate (nucleation theorem). CNT is found to agree reasonably well with the simulation results, whereas LFK leads to large deviations at high temperatures.

scholarly journals Modeling Heat Transport in Systems of Hydrate-Filled Sediments Using Residual Thermodynamics and Classical Nucleation Theory

2021 ◽  
Vol 11 (9) ◽  
pp. 4124
Author(s):  
Mojdeh Zarifi ◽  
Bjørn Kvamme ◽  
Tatiana Kuznetsova
Keyword(s):  
Phase Transition ◽  
Mass Transport ◽  
Heat Transport ◽  
Film Growth ◽  
Growth Models ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Fundamental Properties ◽  
Consistent Model ◽  
Hydrate Phase

As in any other phase transition, hydrate phase transition kinetics involves an implicit coupling of phase transition thermodynamic control and the associated dynamics of mass and heat transport. This work provides a brief overview of certain selected hydrate film growth models with an emphasis on analyzing the hydrate phase transition dynamics. Our analysis is based on the fundamental properties of hydrate and hydrate/liquid water interfaces derived from molecular modeling. We demonstrate that hydrate phase transitions involving water-dominated phases are characterized by heat transport several orders of magnitude faster than mass transport, strongly suggesting that any hydrate phase transition kinetic models based on heat transport will be entirely incorrect as far as thermodynamics is concerned. We therefore propose that theoretical studies focusing on hydrate nucleation and growth should be based on concepts that incorporate all the relevant transport properties. We also illustrate this point using the example of a fairly simplistic kinetic model, that of classical nucleation theory (CNT), modified to incorporate new models for mass transport across water/hydrate interfaces. A novel and consistent model suitable for the calculation of enthalpies is also discussed and appropriate calculations for pure components and relevant mixtures of carbon dioxide, methane, and nitrogen are demonstrated. This residual thermodynamic model for hydrate is consistent with the free energy model for hydrate and ensures that our revised CNT model is thermodynamically harmonious.

Understanding ferroelectric phase formation in doped HfO2 thin films based on classical nucleation theory

Nanoscale ◽  
2019 ◽  
Vol 11 (41) ◽  
pp. 19477-19487 ◽  
Author(s):  
Min Hyuk Park ◽  
Young Hwan Lee ◽  
Cheol Seong Hwang
Keyword(s):  
Thin Films ◽  
Phase Transition ◽  
Phase Formation ◽  
Ferroelectric Phase ◽  
Nucleation Theory ◽  
Classical Nucleation Theory

The nucleation theory is revisited to understand the unexpected ferroelectric phase formation in HfO2-based thin films. Considering the two-step phase transition from amorphous doped HfO2, the ferroelectric phase formation can be understood.

Controlling CoSi2 nucleation : the effect of entropy of mixing

2000 ◽  
Vol 611 ◽  
Author(s):  
C. Detavernier ◽  
R.L. Van Meirhaeghe ◽  
K. Maex ◽  
F. Cardon
Keyword(s):  
Phase Transition ◽  
Free Energy ◽  
Gibbs Free Energy ◽  
Small Difference ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Si Substrate ◽  
Entropy Of Mixing ◽  
Nucleation Barrier

ABSTRACTIt is generally known that nucleation effects strongly influence the CoSi to CoSi2 phase transition. According to classical nucleation theory, the small difference in Gibbs free energy between the CoSi and CoSi2 phase is responsible for the nucleation barrier. Adding elements that are soluble in CoSi and insoluble in CoSi2 will influence the entropy of mixing, and thus change ΔG. In this way, the height of the nucleation barrier may be controlled.By depositing Fe or Ge (respectively replacing Co and Si in the CoSi lattice) in between the Co and the Si substrate, we were able to increase the nucleation barrier. In the presence of Ni, the nucleation barrier is lowered, and low-resistive disilicide is formed at lower temperatures.

6 Bipolar Electrochemistry for Synthesis

2022 ◽  
Author(s):  
E. Villani ◽  
S. Inagi
Keyword(s):  
Materials Science ◽  
Functional Materials ◽  
Anisotropic Materials ◽  
Industrial Applications ◽  
Electrochemical Reactions ◽  
Electrochemical Technology ◽  
Low Concentrations ◽  
Gradient Surfaces ◽  
Bipolar Electrochemistry ◽  
Synergetic Action

Bipolar electrochemistry has gained remarkable interest in recent years, especially in the fields of materials science and organic electrosynthesis. This is due to the interesting features of this particular electrochemical technology, such as the contactless nature of the electrochemical reactions, the use of low concentrations of supporting electrolytes, and the synergetic action of electrophoresis and electrolysis. In this chapter, the most important contributions regarding bipolar electrochemistry for the electrosynthesis of novel functional materials are reviewed. These contributions include the most traditional industrial applications and bipolar reactors for electroorganic synthesis, as well as innovative approaches for the fabrication of anisotropic materials and gradient surfaces. The peculiar characteristics of bipolar electrochemistry in these fields are emphasized.

Sign in / Sign up

Export Citation Format

Share Document