scholarly journals The Anomalous Behavior of Thermodynamic Parameters in the Three Widom Deltas of Carbon Dioxide-Ethanol Mixture

2021 ◽  
Vol 22 (18) ◽  
pp. 9813
Author(s):  
Evgenii Igorevich Mareev ◽  
Alexander Petrovich Sviridov ◽  
Vyacheslav Mihailovich Gordienko
Keyword(s):  
Carbon Dioxide ◽  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Thermodynamic Parameters ◽  
Molar Fraction ◽  
Anomalous Behavior ◽  
Density Fluctuations ◽  
Ethanol Mixture ◽  
The Third ◽  
Wide Range

Using molecular dynamics, we demonstrated that in the mixture of carbon dioxide and ethanol (25% molar fraction) there are three pronounced regions on the p-T diagram characterized by not only high-density fluctuations but also anomalous behavior of thermodynamic parameters. The regions are interpreted as Widom deltas. The regions were identified as a result of analyzing the dependences of density, density fluctuations, isobaric thermal conductivity, and clustering of a mixture of carbon dioxide and ethanol in a wide range of pressures and temperatures. Two of the regions correspond to the Widom delta for pure supercritical carbon dioxide and ethanol, while the third region is in the immediate vicinity of the critical point of the binary mixture. The origin of these Widom deltas is a result of the large mixed linear clusters formation.

scholarly journals Optical Diagnostics of Supercritical CO2 and CO2-Ethanol Mixture in the Widom Delta

Molecules ◽  
2020 ◽  
Vol 25 (22) ◽  
pp. 5424
Author(s):  
Evgenii Mareev ◽  
Timur Semenov ◽  
Alexander Lazarev ◽  
Nikita Minaev ◽  
Alexander Sviridov ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Optical Properties ◽  
Supercritical Co2 ◽  
Cluster Formation ◽  
Mie Scattering ◽  
Density Fluctuations ◽  
Optical Measurements ◽  
Dynamics Simulation ◽  
Ethanol Mixture ◽  
Wide Range

The supercritical CO2 (scCO2) is widely used as solvent and transport media in different technologies. The technological aspects of scCO2 fluid applications strongly depend on spatial–temporal fluctuations of its thermodynamic parameters. The region of these parameters’ maximal fluctuations on the p-T (pressure-temperature) diagram is called Widom delta. It has significant practical and fundamental interest. We offer an approach that combines optical measurements and molecular dynamics simulation in a wide range of pressures and temperatures. We studied the microstructure of supercritical CO2 fluid and its binary mixture with ethanol in a wide range of temperatures and pressures using molecular dynamics (MD) simulation. MD is used to retrieve a set of optical characteristics such as Raman spectra, refractive indexes and molecular refraction and was verified by appropriate experimental measurements. We demonstrated that in the Widom delta the monotonic dependence of the optical properties on the CO2 density is violated. It is caused by the rapid increase of density fluctuations and medium-sized (20–30 molecules) cluster formation. We identified the correlation between cluster parameters and optical properties of the media; in particular, it is established that the clusters in the Widom delta acts as a seed for clustering in molecular jets. MD demonstrates that the cluster formation is stronger in the supercritical CO2-ethanol mixture, where the extended binary clusters are formed; that is, the nonlinear refractive index significantly increased. The influence of the supercritical state in the cell on the formation of supersonic cluster jets is studied using the Mie scattering technique.

Thermal Conductivity of Polyethylene Chains Using Molecular Dynamics Simulations

2008 ◽  
Author(s):  
Asegun Henry ◽  
Gang Chen
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Polymer Chains ◽  
High Thermal Conductivity ◽  
Polymer Materials ◽  
Single Chain ◽  
Wide Range ◽  
Dynamics Simulations ◽  
Limiting Case

We used molecular dynamics simulations to calculate the thermal conductivity of polyethylene chains, by employing the widely used Green-Kubo formula. The simulations use the AIREBO potential and employ periodic boundary conditions to mimic the dynamics of an infinite chain. In this limiting case, we observed that when the simulation domain is large enough the thermal conductivity diverges. The results suggest that single polymer chains intrinsically have high thermal conductivity. Although polymers are generally known to have low thermal conductivity, our observation of divergent thermal conductivity in a single chain suggests that high thermal conductivity polymer materials can be engineered, which would be of interest to a wide range of applications.

Structure and Dynamics of Water Adsorbed in Carbon Nanotubes: A Joint Neutron-Scattering and Molecular-Dynamics Study

2004 ◽  
Vol 840 ◽  
Author(s):  
Nicolas R. de Souza ◽  
Alexander I. Kolesnikov ◽  
Chun-Keung Loong ◽  
Alexander P. Moravsky ◽  
Raouf O. Loutfy ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Hydrogen Bond ◽  
Freezing Point ◽  
Mean Square Displacement ◽  
Anomalous Behavior ◽  
Bulk Water ◽  
Confined Water ◽  
Hydrogen Atoms ◽  
Spatial And Temporal Scales ◽  
Wide Range

ABSTRACTThe advent of nanocarbons, from single- and multiple-walled nanotubes to nanohorns, avails model studies of confined molecules on the nanoscale. Water encapsulated inside the quasi-one-dimensional channels of these materials is expected to exhibit anomalous behavior due to the unique geometry of nanotubes and the weak interaction between the water molecules and the carbon atoms. We have employed neutron small-to-wide angle diffraction, quasielastic and inelastic scattering in conjunction with molecular-dynamics simulations to characterize the structures and dynamics of water adsorbed in open-ended single- and double-walled nanotubes over a wide range of spatial and temporal scales. We find that a square-ice sheet wrapped next to the inner nanotube wall and a water chain in the interior are the key structural elements of nanotube-confined water/ice. This configuration results in a hydrogen-bond connectivity that markedly differs from that in bulk water. This significantly softened hydrogen-bond network manifests in strong energy shifts of the observed and simulated inter- and intra-molecular vibrations. The very large mean-square displacement of hydrogen atoms observed experimentally and the strong anharmonicity inferred from simulations explain the fluid-like behavior at temperatures far below the freezing point of normal water.

Molecular Dynamics Determination of the Lattice Thermal Conductivity of the Cubic Phase of Hafnium Dioxide

2020 ◽  
Vol 27 ◽  
pp. 177-185
Author(s):  
Leila Momenzadeh ◽  
Irina V. Belova ◽  
Graeme E. Murch
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Autocorrelation Function ◽  
Lattice Thermal Conductivity ◽  
Hafnium Dioxide ◽  
Industrial Applications ◽  
Cubic Phase ◽  
Heat Current ◽  
Phonon Modes ◽  
Wide Range

The wide range of industrial applications is the main reason for an increased interest in dioxides such as HfO2. In this study, classical molecular dynamic simulations were performed to calculate the lattice thermal conductivity of the cubic phase of HfO2, over a temperature range of 100-3000 K, based on the Green-Kubo fluctuation method. In this research, the heat current autocorrelation function and lattice thermal conductivity were calculated in the a-direction. The lattice thermal conductivity of the cubic phase of HfO2 was found to be a result of three contributions. These were the optical and acoustic short-range and long-range phonon modes. Comparisons between the results of the research and experimental data when available indicate good agreement. Keywords: lattice thermal conductivity, molecular dynamics, Green-Kubo formalism, heat current autocorrelation function, hafnium dioxid

Thermal Conductivity Estimation of Nano Graphene Using Equilibrium Molecular Dynamics With Andersen and Berendsen Thermostats

2011 ◽  
Author(s):  
Masoud H. Khadem ◽  
Aaron P. Wemhoff
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Potential Model ◽  
Control Method ◽  
Honeycomb Structure ◽  
Heat Current ◽  
Wide Range ◽  
Nano Graphene ◽  
The Impact ◽  
Covalent Interactions

The impact of the temperature control method on the thermal conductivity of a small sheet of graphene is studied. Equilibrium Molecular Dynamics (EMD) simulations are used to evaluate the heat current fluctuations and thermal conductivity calculations. The Tersoff potential model is used to determine the covalent interactions between carbon atoms of the graphene’s honeycomb structure. Green-Kubo relations are employed to estimate thermal conductivity values. Andersen and Berendsen thermostats are separately utilized to obtain a desired temperature for the canonical (NVT) ensemble. The influence of the chosen thermostat on the estimated thermal conductivity found to be significant. The wide range of computational and experimental results shows that further work is required to confidently determine the thermal conductivity of this material.

The Colonial Documentary Film in South and South-East Asia

2017 ◽  
Keyword(s):  
East Asia ◽  
Subject Matter ◽  
Documentary Film ◽  
East Asian ◽  
South East Asia ◽  
Post Colonial ◽  
Historical Perspectives ◽  
The Third ◽  
Wide Range ◽  
Global Understanding

Writing from a wide range of historical perspectives, contributors to the anthology shed new light on historical, theoretical and empirical issues pertaining to the documentary film, in order to better comprehend the significant transformations of the form in colonial, late colonial and immediate post-colonial and postcolonial times in South and South-East Asia. In doing so, this anthology addresses an important gap in the global understanding of documentary discourses, practices, uses and styles. Based upon in-depth essays written by international authorities in the field and cutting-edge doctoral projects, this anthology is the first to encompass different periods, national contexts, subject matter and style in order to address important and also relatively little-known issues in colonial documentary film in the South and South-East Asian regions. This anthology is divided into three main thematic sections, each of which crosses national or geographical boundaries. The first section addresses issues of colonialism, late colonialism and independence. The second section looks at the use of the documentary film by missionaries and Christian evangelists, whilst the third explores the relation between documentary film, nationalism and representation.

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