scholarly journals Enrichment at Vapour–liquid Interfaces of Mixtures: Establishing a Link between Nanoscopic and Macroscopic Properties

2021 ◽  
Author(s):  
Simon Stephan ◽  
Hans Hasse
Keyword(s):  
Density Functional ◽  
Phase Behaviour ◽  
Model Parameters ◽  
Gradient Theory ◽  
Liquid Interfaces ◽  
Density Profiles ◽  
Macroscopic Properties ◽  
Equilibrium Data ◽  
Data Points ◽  
Available Information

Component density profiles at vapour–liquid interfaces of mixtures can exhibit a non-monotonic behaviour with a maximum that can be many times larger than the densities in the bulk phases. This is called enrichment and is usually only observed for low-boiling components. The enrichment is a nanoscopic property which can presently not be measured experimentally – in contrast to the classical Gibbs adsorption. The available information on the enrichment stems from molecular simulations, density gradient theory, or density functional theory. The enrichment is highly interesting as it is suspected to influence the mass transfer across interfaces. In the present work, we review the literature data and the existing knowledge on this phenomenon and propose an empirical model to establish a link between the nanoscopic enrichment and macroscopic properties – namely vapour–liquid equilibrium data. The model parameters were determined from a fit to a dataset on the enrichment in about 100 binary Lennard-Jones model mixtures that exhibit different types of phase behaviour, which has recently become available. The model is then tested on the entire set of enrichment data that is available in the literature, which includes also mixtures containing non-spherical, polar, and H-bonding components. The model predicts the enrichment data from the literature (2,000 data points) with an AAD of about 16%, which is below the uncertainty of the enrichment data. This establishes a direct link between measurable macroscopic properties and the nanoscopic enrichment and enables predictions of the enrichment at vapour–liquid interfaces from macroscopic data alone.

scholarly journals Enrichment of Components at Vapour-Liquid Interfaces: A Study by Molecular Simulation and Density Gradient Theory

2021 ◽  
Author(s):  
Simon Stephan ◽  
Kai Langenbach ◽  
Hans Hasse
Keyword(s):  
Mass Transfer ◽  
Density Gradient ◽  
Density Functional ◽  
Liquid Interface ◽  
Bulk Liquid ◽  
Gradient Theory ◽  
Total Density ◽  
Liquid Interfaces ◽  
Separation Processes ◽  
Density Gradient Theory

In separation processes not only thermodynamic bulk but also interfacial properties play a crucial role. Inclassical theory, a vapour-liquid interface is a two-dimensional object. In reality it is a region in whichproperties change over a few nanometres and the density changes continuously from its liquid bulk to its gasbulk value. Many mixtures show unexpected effects in that transition region. While the total density changesmonotonously from the bulk vapour to the bulk liquid, this does not hold for the molarities of the components.The molarities of the light boiling component can have a distinct maximum at the interface. That maximumwould be an insurmountable obstacle to mass transfer according to Fickian theory. Even if that argument isnot adopted, it shows that there is good reason to believe that the maximum may affect mass transfer and,hence, fluid separation processes like absorption or distillation. Unfortunately, there are currently noexperimental methods that can be used for direct studies of density profiles in such interfacial regions. Butsuch data can be obtained with theoretical methods, namely with molecular dynamics simulations (MD) aswell as with density gradient theory (DGT) or with density functional theory (DFT) combined with an equationof state (EOS).Studies from our group on the vapour-liquid interface of several real mixtures and a model fluid using thesemethods yield consistent results and reveal an important enrichment in some cases. Strong enrichment isfound at vapour-liquid interfaces in the systems in which one of the components is supercritical. These resultsindicate that mixtures, which are typical for absorption processes usually show an important enrichment,whereas this is not the case for mixtures that are typically separated by distillation. Possible consequences ofthis finding for the modelling of these separation processes are discussed.

Swollen micelles and alcohol–surfactant co-adsorption: structures and mechanisms from liquid- and solid-state 1H–1H NMR spectroscopy

2017 ◽  
Vol 19 (11) ◽  
pp. 7708-7713 ◽  
Author(s):  
Christian Totland ◽  
Anne Marit Blokhus
Keyword(s):  
Solid State ◽  
Nmr Spectroscopy ◽  
1H Nmr ◽  
1H Nmr Spectroscopy ◽  
Co Adsorption ◽  
Phase Behaviour ◽  
Liquid Interfaces ◽  
Adsorption Behaviour ◽  
Mixtures Of Surfactants ◽  
Solid Liquid

Mixtures of surfactants and medium-chained alcohols display an anomalous phase behaviour, with the formation of swollen micelles in mid-range surfactant concentrations. Such alcohols also affect the aggregation and adsorption behaviour of surfactants at solid–liquid interfaces.

Unsupervised labelling of remote sensing images based on force field clustering

2021 ◽  
pp. 1-14
Author(s):  
Zhenggang Wang ◽  
Jin Jin
Keyword(s):  
Remote Sensing ◽  
Force Field ◽  
Image Data ◽  
Model Parameters ◽  
Remote Sensing Images ◽  
Initial Cluster ◽  
Data Points ◽  
Global Optimal ◽  
Density Force

Remote sensing image segmentation provides technical support for decision making in many areas of environmental resource management. But, the quality of the remote sensing images obtained from different channels can vary considerably, and manually labeling a mass amount of image data is too expensive and Inefficiently. In this paper, we propose a point density force field clustering (PDFC) process. According to the spectral information from different ground objects, remote sensing superpixel points are divided into core and edge data points. The differences in the densities of core data points are used to form the local peak. The center of the initial cluster can be determined by the weighted density and position of the local peak. An iterative nebular clustering process is used to obtain the result, and a proposed new objective function is used to optimize the model parameters automatically to obtain the global optimal clustering solution. The proposed algorithm can cluster the area of different ground objects in remote sensing images automatically, and these categories are then labeled by humans simply.

scholarly journals The Energetic Viability of Δ1-Piperideine Dimerization in Lysine-derived Alkaloid Biosynthesis

Metabolites ◽  
2018 ◽  
Vol 8 (3) ◽  
pp. 48 ◽  
Author(s):  
Hajime Sato ◽  
Masanobu Uchiyama ◽  
Kazuki Saito ◽  
Mami Yamazaki
Keyword(s):  
Density Functional ◽  
Indole Alkaloid ◽  
Alkaloid Biosynthesis ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Reaction Proceeds ◽  
Acidic Conditions ◽  
Dimerization Reaction ◽  
Available Information ◽  
Skeleton Formation

Lys-derived alkaloids widely distributed in plant kingdom have received considerable attention and have been intensively studied; however, little is known about their biosynthetic mechanisms. In terms of the skeleton formation, for example, of quinolizidine alkaloid biosynthesis, only the very first two steps have been identified and the later steps remain unknown. In addition, there is no available information on the number of enzymes and reactions required for their skeletal construction. The involvement of the Δ 1 -piperideine dimerization has been proposed for some of the Lys-derived alkaloid biosyntheses, but no enzymes for this dimerization reaction have been reported to date; moreover, it is not clear whether this dimerization reaction proceeds spontaneously or enzymatically. In this study, the energetic viability of the Δ 1 -piperideine dimerizations under neutral and acidic conditions was assessed using the density functional theory computations. In addition, a similar type of reaction in the dipiperidine indole alkaloid, nitramidine, biosynthesis was also investigated. Our findings will be useful to narrow down the candidate genes involved in the Lys-derived alkaloid biosynthesis.

scholarly journals Grand-Canonical Approach to Density Functional Theory of Electrocatalytic Systems: Thermodynamics of Solid-Liquid Interfaces at Constant Ion and Electrode Potentials

2018 ◽  
Author(s):  
Marko Melander ◽  
Mikael Kuisma ◽  
Thorbjørn Christensen ◽  
Karoliina Honkala
Keyword(s):  
Density Functional ◽  
Canonical Ensemble ◽  
Coarse Graining ◽  
Grand Canonical Ensemble ◽  
Liquid Interfaces ◽  
Functional Theory ◽  
Electrode Potentials ◽  
Solid Liquid ◽  
Electrochemical Interfaces ◽  
Grand Canonical

Properties of solid-liquid interfaces are of immense importance for electrocatalytic and electrochemical systems but modelling such interfaces at the atomic level presents a serious challenge and approaches beyond standard methodologies are needed. An atomistic computational scheme needs treat at least part of the system quantum mechanically to include adsorption and reactions while the entire system is in thermal equilibrium. The experimentally relevant macroscopic control variables are temperature, electrode potential, choice of the solvent and ions and these need to be explicitly included in the computational model as well; this calls for an thermodynamic ensemble with fixed ion and electrode potentials. In this work a general framework within density functional theory with fixed electron and ion chemical potentials in the grand canonical ensemble is established for modelling electrocatalytic and electrochemical interfaces. Starting from a fully quantum mechanical description of nuclei and electrons, a systematic coarse-graining is employed to establish various computational schemes including i) the combination of classical and electronic density functional theories within the grand canonical ensemble and ii) on the simplest level a chemically and physically sound way to obtain the (modified) Poisson-Boltzmann (mPB) implicit solvent model. The detailed and rigorous derivation clearly establishes which approximations are needed for coarse-graining as well as highlights which details and interactions are omitted in vein of computational feasibility. The transparent approximations also allow removing some the constraints and coarse-graining if needed. We implement various mPB models in the GPAW code and test their capabilities to model capacitance of electrochemical interfaces as well as study different approaches for modelling partly periodic charged systems. Our rigorous and well-defined DFT coarse-graining scheme to continuum electrolytes highlights the inadequacy of current linear dielectric models for treating properties of the electrochemical interface.<br><br>

scholarly journals A Critical Assessment of Methods for the Intrinsic Analysis of Liquid Interfaces: 2. Density Profiles

2010 ◽  
Vol 114 (43) ◽  
pp. 18656-18663 ◽  
Author(s):  
Miguel Jorge ◽  
György Hantal ◽  
Pál Jedlovszky ◽  
M. Natália D. S. Cordeiro
Keyword(s):  
Critical Assessment ◽  
Liquid Interfaces ◽  
Density Profiles

scholarly journals Grand-Canonical Approach to Density Functional Theory of Electrocatalytic Systems: Thermodynamics of Solid-Liquid Interfaces at Constant Ion and Electrode Potentials

2018 ◽  
Author(s):  
Marko Melander ◽  
Mikael Kuisma ◽  
Thorbjørn Christensen ◽  
Karoliina Honkala
Keyword(s):  
Density Functional ◽  
Canonical Ensemble ◽  
Coarse Graining ◽  
Grand Canonical Ensemble ◽  
Liquid Interfaces ◽  
Functional Theory ◽  
Electrode Potentials ◽  
Solid Liquid ◽  
Electrochemical Interfaces ◽  
Grand Canonical

Properties of solid-liquid interfaces are of immense importance for electrocatalytic and electrochemical systems but modelling such interfaces at the atomic level presents a serious challenge and approaches beyond standard methodologies are needed. An atomistic computational scheme needs treat at least part of the system quantum mechanically to include adsorption and reactions while the entire system is in thermal equilibrium. The experimentally relevant macroscopic control variables are temperature, electrode potential, choice of the solvent and ions and these need to be explicitly included in the computational model as well; this calls for an thermodynamic ensemble with fixed ion and electrode potentials. In this work a general framework within density functional theory with fixed electron and ion chemical potentials in the grand canonical ensemble is established for modelling electrocatalytic and electrochemical interfaces. Starting from a fully quantum mechanical description of nuclei and electrons, a systematic coarse-graining is employed to establish various computational schemes including i) the combination of classical and electronic density functional theories within the grand canonical ensemble and ii) on the simplest level a chemically and physically sound way to obtain the (modified) Poisson-Boltzmann (mPB) implicit solvent model. The detailed and rigorous derivation clearly establishes which approximations are needed for coarse-graining as well as highlights which details and interactions are omitted in vein of computational feasibility. The transparent approximations also allow removing some the constraints and coarse-graining if needed. We implement various mPB models in the GPAW code and test their capabilities to model capacitance of electrochemical interfaces as well as study different approaches for modelling partly periodic charged systems. Our rigorous and well-defined DFT coarse-graining scheme to continuum electrolytes highlights the inadequacy of current linear dielectric models for treating properties of the electrochemical interface.<br><br>

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