1,721,162 research outputs found
Molecular Modelling of electrolytes transport across nanoporous membranes
No full textLes procédés de séparation membranaires sont des techniques particulièrement adaptées aux exigences écologiques et industrielles en matière de traitement de l'eau. Parmi les différentes techniques de séparation existantes, la nanofiltration est un procédé économique permettant le dessalement et l'adoucissement de l'eau. En dépit du nombre croissant de travaux académiques ou industriels portant sur la nanofiltration ces dernières années, les phénomènes physiques impliqués dans le transport de solutés (en particuliers les sels) à travers les matériaux nanoporeux restent mal compris. En effet, les matériaux sont des membranes de polymère dont la structure est complexe et méconnue. Les propriétés des liquides en milieu confiné présentent de plus des propriétés inattendues. L'utilisation d'outils numériques permet d'explorer et d'améliorer la compréhension des mécanismes de transport à travers des membranes. Parmi les différentes approches existantes, les simulations de type dynamique moléculaire permettent de sonder les propriétés des liquides confinées à l'échelle moléculaire. L'objectif de cette thèse est d'analyser les propriétés de solutions aqueuses d'électrolytes confinées dans un nanopore modèle par simulation de dynamique moléculaire. Les systèmes étudiés sont constitués d'un pore de silice connecté à deux réservoirs contenant de l'eau salée. Deux types de simulations ont été réalisés. Au cours d'une simulation dite « à l'équilibre », les propriétés structurales, diélectriques et dynamiques des liquides ont été étudiées. Au cours des simulations ''hors-équilibre'', une différence de pression est appliquée entre les réservoirs afin de générer un écoulement. Les propriétés de transport de l'eau et des sels à travers le nanopore ont été étudiées. Ce travail s'inscrit dans le cadre du projet MUTINA financé par l'Agence Nationale de la Recherche (ANR 2011 BS09 002) portant sur la modélisation multi-échelle du transport d'ions en nanofiltration.Membrane processes are very powerful techniques in term of water treatment. Nanofiltration is a recent membrane process mainly used for water desalination and water softening. Although nanofiltration has attracted increasing attention over the recent years, physical phenomenon related to species (especially aqueous salts) inside the membranes are still poorly understood at the nanoscale. The membranes used in a nanofiltration process (polymeric membranes) are indeed very complex and little is known about their structure. Moreover, liquids in a confined phase exhibit very different behaviour with respect from a bulk phase. In order to investigate the transport mechanisms, modelling tools are often used to reproduce the liquids and membranes behaviour. Molecular dynamic simulations are very useful in that case to gain insight into the liquid properties at the molecular scale. The aim of this thesis is to improve the understanding of the electrolytes transport inside a model nanopore. For this purpose, molecular simulations were carried out to simulate two kind of systems composed of pore connected to reservoirs filled of water and salts. On one hand, we performed equilibrium simulations to analyse the structural, dielectric and dynamic properties of confined liquids. On the other hand, non-equilibrium simulations were performed to generate a pressure-driven fluid flow to investigate water and ions transport. This work is part of the MUTINA project founded by the French National Research Agency for Research (ANR 2011 BS09 002) about multi-scale modelling of ion transport in nanofiltration
Molecular modeling of membranes for nanofiltration in non-aqueous media
No full textAu cours de la thèse, des modèles microscopiques de différentes membranes polymériques compatibles avec la nanofiltration organique sont tout d’abord développés (polyimides et polymères à microporosité intrinsèque tels que le PIM-1). Les membranes élaborées sont ensuite utilisées dans des simulations de dynamique moléculaire dans lesquelles elles sont mises au contact des solvants usuels utilisés dans les industries agroalimentaires, chimiques et pharmaceutiques (Méthanol, Ethanol, Acétone et Toluène) afin d'étudier les interactions solvant / matériau. Elles sont complétées par des simulations de dynamique moléculaire hors équilibre afin d'étudier le transport sous pression et ainsi de déterminer la perméance des membranes vis-à-vis des différents solvants.During the thesis, microscopic models of different polymer membranes compatible with organic nanofiltration are first developed (polyimides, and polymers with intrinsic microporosity such as PIM-1). The membranes developed are then used in molecular dynamics simulations in which they are brought into contact with common solvents used in the food, chemical and pharmaceutical industries (Methanol, Ethanol, Acetone and Toluene) to study solvent/material interactions. They are supplemented by non-equilibrium molecular dynamics simulations which make it possible to study pressure-driven transport and thus to determine the permeance of membranes with respect to different solvents
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Nanoconfined gases, liquids and liquid crystals in porous materials
No full textInternational audienceWe propose here to give an overview of gases and liquids adsorption in the materials of Institute Lavoisier (MIL)-101(Cr), MIL-53(Cr) and silica materials. We present some recent results of systems of interests such as the H2 adsorption in MIL-101(Cr) and CO2 and H2S adsorption in the MIL-53(Cr) material. In addition, we will examine the sensitivity in water force field for water adsorption in hydrophilic and hydrophobic silica nanopores and we evaluate the Gay-Berne liquid crystal adsorption in the smooth and rough pores
Méthodologies de simulation moléculaire pour le calcul de grandeurs thermodynamiques d'association : théorie et application à différents types de complexes
No full textThe development of new methods of perturbation, thermodynamic integration and potential of mean force allowed us to characterize thermodynamically (delta G r, r delta H, delta S r) of the association process between a macrocycle and different types of cations in aqueous solution. Different methodologies have been developed based on the nature of non-covalent interactions involved between the macrocycle and the cation (-pi interaction, electrostatic, van der Waals). When the magnitudes of association were calculated in agreement with experiment, the appearance of complex molecular description and associated phenomena has enabled the coupling between the microscopic and macroscopic thus completing the analysis of the thermodynamic.Le développement de nouvelles méthodes de perturbation, d'intégration thermodynamique et de potentiel de forces moyennes nous a permis de caractériser thermodynamiquement (delta r G, delta r H, delta r S) des processus d'association entre un macrocycle et différents types de cations en solution aqueuse. Différentes méthodologies ont été développées en fonction de la nature des interactions non-covalentes mises en jeu entre le macrocycle et le cation (interaction-pi, électrostatique, van des Waals). Lorsque les grandeurs d'association calculées étaient en accord avec l'expérience, l'aspect description moléculaire des complexes et des phénomènes associés a permis le couplage entre le microscopique et le macroscopique complétant ainsi l'analyse des grandeurs thermodynamiques
Molecular origin of the prepeak in the structure factor of alcohols
No full textInternational audiencePrepeak in the structure factor of alcohols is known for a half century and was attributed to one of two mechanisms (i) self-assembly in aggregates and (ii) existence of spatial heterogeneity. Although both explnations are often argued the molecular origin is yet unclear. In this work, molecular dynamics simulation of neat alcohols and their mixtures in the presence of an apolar liquid in bulk and in confined phases is performed to unveil and to clarify the origin of the prepeak at the molecular scale. Unambiguously, we show that the existence of the prepeak is the result of the self-assembly in clusters leading to long-range correlations rather than the spatial heterogeneity. We also establish that the confinement of neat liquids at the nanoscale does not erase the clustering and the prepeak but strongly reduce the spatial heterogeneity. Regarding the binary alcohol/toluene mixtures, we highlight the possibility to erase the clustering and the spatial heterogeneity from nanoconfinement inducing the formation of a core−shell structure. By tuning the interfacial chemistry and pore size, we shed light on the possibility to control the spatial heterogeneity, the self-assembly, and the microphase separation. © 2020 American Chemical Societ
Metal-organic-framework transparency to water interactions for enhanced CO2 adsorption
No full textInternational audienceToday, the capture of post-combustion CO2 has become a global priority, particularly in order to curb rising temperatures in the coming decades. CO2 physisorption in porous materials such as metal-organic frameworks is likely one of the most effective approaches to addressing this problem, thanks to its low energy requirement and improved regeneration process. In this study, I investigated CO2 capture in humid conditions using the Al-MIL-53-TDC metal-organic framework through molecular simulations. I observed that water filling occurs gradually through pore capillary condensation. Remarkably, the presence of water (at a hydration rate of 4.4 wt%) resulted in a significant increase of 283% in the adsorbed amount of CO2 (1.8 mmol/g at 0.2 bar) due to a unique transparency property. The thin molecular walls between the uniaxial channels enable van der Waals and electrostatic interactions between water and adsorbed gas, which allow media on opposite sides of the walls to influence each other. The increase in isosteric heat of adsorption (46 kJ/mol) is attributed to the contribution of water/water energy resulting from the truncation of the hydration shell of water. This truncation increases the number of hydrogen bonds, which can be linked to a kosmotropic effect. Additionally, the selectivity of hydrated Al-MIL-53-TDC for CO2/N2 increased by 185% at 0.2 bar (composition 20:80), compared to the unhydrated MOF material with QsT < 50 kJ/mol
- …
