An Atomistic Simulation Study of the Role of Asperities and Indentations on Heterogeneous Bubble Nucleation

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Brian R. Novak ◽  
Edward J. Maginn ◽  
Mark J. McCready
Keyword(s):  
Heat Flux ◽  
Atomistic Simulation ◽  
Surface Defects ◽  
Constant Heat Flux ◽  
Bubble Nucleation ◽  
Nonequilibrium Molecular Dynamics ◽  
Lennard Jones ◽  
Dynamics Simulations ◽  
Fluid Interaction

Heterogeneous bubble nucleation was studied on surfaces having nanometer scale asperities and indentations as well as different surface-fluid interaction energies. Nonequilibrium molecular dynamics simulations at constant normal stress and either temperature or heat flux were carried out for the Lennard–Jones fluid in contact with a Lennard–Jones solid. When surface defects were of the same size or smaller than the estimated critical nucleus (the smallest nucleus whose growth is energetically favored) size of 1000–2000Å3, there was no difference between the defected surfaces and atomically smooth surfaces. On the other hand, surfaces with significantly larger indentations had nucleation rates that were about two orders of magnitude higher than the systems with small defects. Moreover, nucleation was localized in the large indentations. This localization was greatest under constant heat flux conditions and when the solid-fluid interactions were weak. The results suggest strategies for enhancing heterogeneous bubble nucleation rates as well as for controlling the location of nucleation events.

Controlling Thermal Conductivity of Alloys via Atomic Ordering

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
John C. Duda ◽  
Timothy S. English ◽  
Donald A. Jordan ◽  
Pamela M. Norris ◽  
William A. Soffa
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Nonequilibrium Molecular Dynamics ◽  
Melt Temperature ◽  
Lennard Jones ◽  
Thermodynamic Conditions ◽  
Order Of Magnitude ◽  
Fixed Composition ◽  
Dynamics Simulations

Many random substitutional solid solutions (alloys) will display a tendency to atomically order given the appropriate kinetic and thermodynamic conditions. Such order–disorder transitions will result in major crystallographic reconfigurations, where the atomic basis, symmetry, and periodicity of the alloy change dramatically. Consequently, phonon behavior in these alloys will vary greatly depending on the type and degree of ordering achieved. To investigate these phenomena, the role of the order–disorder transition on phononic transport properties of Lennard–Jones type binary alloys is explored via nonequilibrium molecular dynamics simulations. Particular attention is paid to regimes in which the alloy is only partially ordered. It is shown that by varying the degree of ordering, the thermal conductivity of a binary alloy of fixed composition can be tuned across an order of magnitude at 10% of the melt temperature, and by a factor of three at 40% of the melt temperature.

Heat controlling in the mass-graded harmonic lattices with double-well on-site potential

2018 ◽  
Vol 32 (20) ◽  
pp. 1850217
Author(s):  
Peng Kong ◽  
Zhengzheng Wei ◽  
Tao Hu ◽  
Yi Tang
Keyword(s):  
Molecular Dynamics ◽  
Heat Flux ◽  
Power Spectrum ◽  
Molecular Dynamics Simulations ◽  
Heat Transport ◽  
Nonequilibrium Molecular Dynamics ◽  
Thermal Rectification ◽  
Average Temperature ◽  
New Type ◽  
Dynamics Simulations

Using nonequilibrium molecular dynamics simulations, we investigate thermal rectification in mass-graded lattices with a new type on-site potential which has a physical picture of the double-well. By adjusting the ratio of harmonic on-site potential and anharmonic on-site potential, we could obtain the optimal heat transport and the best thermal rectification. In addition, we observe the reversal thermal rectification by changing the ratio of on-site potential and analyzes the mechanism of thermal rectification through the power spectrum. At last, we also study the heat flux and thermal rectification in a different case of average temperature and mass gradient.

Superlattice Analysis for Tailored Thermal Transport Characteristics

2006 ◽  
Author(s):  
E. S. Landry ◽  
A. J. H. McGaughey ◽  
M. I. Hussein
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Direct Method ◽  
Continuum Theory ◽  
Lennard Jones ◽  
Constituent Species ◽  
The Cross ◽  
Dynamics Simulations ◽  
Superlattice Period

Molecular dynamics simulations and the Green-Kubo method are used to predict the thermal conductivity of binary Lennard-Jones superlattices and alloys. The superlattice thermal conductivity trends are in agreement with those obtained through the direct method, verifying that the Green-Kubo method can be used to examine thermal transport in heterostructures. The simulation temperature and the constituent species are fixed while the superlattice period structure is varied with the goals of (i) minimizing the cross-plane thermal conductivity and (ii) maximizing the ratio of in-plane to cross-plane thermal conductivities. The superlattice thermal conductivity in both the cross-plane and in-plane directions is found to be greater than the corresponding alloy value and less than the value predicted from continuum theory. The anisotropy of the thermal conductivity tensor is found to be at a maximum for a superlattice with a uniform layer thickness. Lattice dynamics calculations are used to investigate the role of optical phonons in the thermal transport.

On the Role of Solvent in the Formation of Vacancies on Ibuprofen Crystal Facets

2021 ◽  
Author(s):  
Veselina Marinova ◽  
Geoffrey P. F. Wood ◽  
Ivan Marziano ◽  
Matteo Salvalaglio
Keyword(s):  
Surface Defects ◽  
Defect Formation ◽  
Energetic Cost ◽  
Crystal Facet ◽  
Mechanism Of Defect Formation ◽  
Surface Vacancy ◽  
Racemic Ibuprofen ◽  
Dynamics Simulations ◽  
Role Of Solvent

Surface defects play a crucial role in the process of crystal growth, as the incorporation of growth units generally takes place on under-coordinated sites on the growing crystal facet. In this work, we use molecular dynamics simulations to obtain information on the role of the solvent in the roughening of three morphologically-relevant crystal faces of form I of racemic ibuprofen. To this aim, we devise a computational strategy based on combining independent Well Tempered Metadynamics with Mean Force Integration. This approach enables us to evaluate the energetic cost associated with the formation of a surface vacancy for a set of ten solvents, covering a range of polarities and hydrogen-bonding ability. We find that both the mechanism of defect formation on these facets and the work associated with the process are indeed markedly solvent-dependent. The methodology developed in this work has been designed with the aim of capturing solvent effects at the atomistic scale while maintaining the computational efficiency necessary for implementation in high-throughput computational screenings of crystallization solvents.

scholarly journals Effective Determination of Coexistence Curves using Reversible-Scaling Molecular Dynamics Simulations

2000 ◽  
Vol 653 ◽  
Author(s):  
Maurice de Koning ◽  
Alex Antonelli ◽  
Sidney Yip
Keyword(s):  
Molecular Dynamics ◽  
Md Simulation ◽  
Melting Curve ◽  
Coexistence Curve ◽  
Nonequilibrium Molecular Dynamics ◽  
Computational Cell ◽  
Clapeyron Equation ◽  
Lennard Jones ◽  
Dynamics Simulations

AbstractWe present a simulation technique that allows the calculation of a phase coexistence curve from a single nonequilibrium molecular dynamics (MD) simulation. The approach is based on the simultaneous simulation of two coexisting phases, each in its own computational cell, and the integration of the relevant Clausius-Clapeyron equation starting from a known coexistence point. As an illustration of the effectiveness of our approach we apply the method to explore the melting curve in the Lennard-Jones phase diagram.

scholarly journals Influence of Dispersive Long-range Interactions on Properties of Vapour–liquid Equilibria and Interfaces of Binary Lennard-Jones Mixtures

2021 ◽  
Author(s):  
Simon Stephan ◽  
Hans Hasse
Keyword(s):  
Lateral Direction ◽  
Contact Processes ◽  
Lennard Jones ◽  
Flat Substrate ◽  
Long Range Interactions ◽  
Minor Part ◽  
Dynamics Simulations ◽  
A Minor ◽  
Work Done ◽  
Fluid Interaction

Liquid lubricants play an important role in contact processes; for example, they reduce friction and cool the contact zone. To gain better understanding of the influence of lubrication on the nanoscale, both dry and lubricated scratching processes in a model system are compared in the present work using molecular dynamics simulations. The entire range between total dewetting and total wetting is investigated by tuning the solid–fluid interaction energy. The investigated scratching process consists of three sequential movements: A cylindrical indenter penetrates an initially flat substrate, then scratches in the lateral direction, and is finally retracted out of the contact with the substrate. The indenter is fully submersed in the fluid in the lubricated cases. The substrate, the indenter, and the fluid are described by suitably parametrized Lennard–Jones model potentials. The presence of the lubricant is found to have a significant influence on the friction and on the energy balance of the process. The thermodynamic properties of the lubricant are evaluated in detail. A correlation of the simulation results for the profiles of the temperature, density, and pressure of the fluid in the vicinity of the chip is developed. The work done by the indenter is found to mainly dissipate and thereby heat up the substrate and eventually the fluid. Only a minor part of the work causes plastic deformation of the substrate.

Role of Chemical Ordering on Phononic Transport in Binary Alloys

2011 ◽  
Author(s):  
John C. Duda ◽  
Timothy S. English ◽  
William A. Soffa ◽  
Donald A. Jordan ◽  
Pamela M. Norris
Keyword(s):  
Order Parameter ◽  
Binary Alloys ◽  
Range Order Parameter ◽  
Lennard Jones ◽  
Chemical Ordering ◽  
Thermodynamic Conditions ◽  
Order Of Magnitude ◽  
Non Equilibrium Molecular Dynamics ◽  
Dynamics Simulations

Many random substitutional solid solutions (alloys) will display a tendency to chemically order given the appropriate kinetic and thermodynamic conditions. Such order-disorder transitions will result in major crystallographic reconfigurations, where the atomic basis, symmetry, and periodicity of the alloy change dramatically. Consequently, phonon behavior in these alloys will vary greatly depending on the type and degree of ordering achieved. To investigate these phenomena, the role of the order-disorder transition on phononic transport properties of Lennard-Jones type binary alloys is explored via non-equilibrium molecular dynamics simulations. Particular attention is paid to regimes in which the alloy is only partially ordered. It is shown that, through exploitation of the long-range order parameter, thermal conductivity of binary alloys can be effectively tuned across half an order of magnitude at low-to-moderate temperatures.

scholarly journals On the role of the Knudsen layer in rapid granular flows

2007 ◽  
Vol 585 ◽  
pp. 73-92 ◽  
Author(s):  
J. E. GALVIN ◽  
C. M. HRENYA ◽  
R. D. WILDMAN
Keyword(s):  
Heat Flux ◽  
Granular Flows ◽  
Order Theory ◽  
Knudsen Layer ◽  
Navier Stokes ◽  
Experimental Systems ◽  
Theoretical Predictions ◽  
Flux Measurements ◽  
Dynamics Simulations

A combination of molecular dynamics simulations, theoretical predictions and previous experiments are used in a two-part study to determine the role of the Knudsen layer in rapid granular flows. First, a robust criterion for the identification of the thickness of the Knudsen layer is established: a rapid deterioration in Navier–Stokes order prediction of the heat flux is found to occur in the Knudsen layer. For (experimental) systems in which heat flux measurements are not easily obtained, a rule-of-thumb for estimating the Knudsen layer thickness follows, namely that such effects are evident within 2.5 (local) mean free paths of a given boundary. Secondly, comparisons of simulation and experimental data with Navier–Stokes order theory are used to provide a measure as to when Knudsen-layer effects become non-negligible. Specifically, predictions that do not account for the presence of a Knudsen layer appear reliable for Knudsen layers collectively composing up to 20% of the domain, whereas deterioration of such predictions becomes apparent when the domain is fully comprised of the Knudsen layer.

scholarly journals The Influence of Lubrication and the Solid-fluid Interaction on Thermodynamic Properties in a Nanoscopic Scratching Process

2021 ◽  
Author(s):  
Simon Stephan ◽  
Maximilian Dyga ◽  
Herbert Urbassek ◽  
Hans Hasse
Keyword(s):  
Thermodynamic Properties ◽  
Lateral Direction ◽  
Contact Processes ◽  
Lennard Jones ◽  
Flat Substrate ◽  
Minor Part ◽  
Dynamics Simulations ◽  
A Minor ◽  
Work Done ◽  
Fluid Interaction

Liquid lubricants play an important role in contact processes; for example, they reduce friction and cool the contact zone. To gain better understanding of the influence of lubrication on the nanoscale, both dry and lubricated scratching processes in a model system are compared in the present work using molecular dynamics simulations. The entire range between total dewetting and total wetting is investigated by tuning the solid–fluid interaction energy. The investigated scratching process consists of three sequential movements: A cylindrical indenter penetrates an initially flat substrate, then scratches in the lateral direction, and is finally retracted out of the contact with the substrate. The indenter is fully submersed in the fluid in the lubricated cases. The substrate, the indenter, and the fluid are described by suitably parametrized Lennard–Jones model potentials. The presence of the lubricant is found to have a significant influence on the friction and on the energy balance of the process. The thermodynamic properties of the lubricant are evaluated in detail. A correlation of the simulation results for the profiles of the temperature, density, and pressure of the fluid in the vicinity of the chip is developed. The work done by the indenter is found to mainly dissipate and thereby heat up the substrate and eventually the fluid. Only a minor part of the work causes plastic deformation of the substrate.

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