Search

Globalized formulations have been proposed since at least 40 years for taking into account Soret and Dufour effects in buoyancy-driven instabilities in binary fluids. The purpose of this note is to explain what is the physical meaning of these formulations and how useful they can be.

International audience; Despite its importance, the description of liquid–liquid extraction is made difficult because the link between the experimental methods and the interactions present in the solution is not direct due to the many organisation phenomena that can occur. We propose a new methodology combining microcalorimetric measurements and molecular modelling to better describe the nature and strength of these interactions in these complex fluids by focusing on extractant-diluent mixtures (N,N-dialkylamides + n-alkanes). Enthalpies of dilution were obtained by microcalorimetric measurements at 298 K for each n-dodecane and n-heptane with DEHiBA and for n-dodecane with DEHBA. These results have been compared, thanks to a new method that we present here, to molecular dynamics simulations carried out on these same systems. We especially analyzed the influence of the alkyl branching of the extracting molecules and the role of the diluent. Globally, the excess enthalpy is such that these mixtures are energetically not very different from regular solutions but the detailed balance shows an important attraction between the extractants, which can lead to the formation of macromolecular entities favouring extraction. Calorimetry appears to be a method of choice for linking experiments and molecular modelling in these complex liquid mixtures, and experimental developments could benefit from using it more often, especially to validate force-fields.

Liquid crystals are found in important technological applications that are now maturing. The discovery in 2011 of a new nematic phase, the Twist Bend nematic (NTB) phase, could lead to a renewal in the field of liquid crystals applications requiring fast response times. However, the NTB phase is usually found at high temperatures and its alignment is exceedingly difficult to achieve, even in thin cells. The work of this thesis focuses on solving these two problems.The bad alignment of NTB phase in planar cells gives rise to unusual textures such as periodic stripes. In order to understand the origin of those textures, we changed the nature of the alignment layers as well as their parameters (anchoring forces, pretilt…). Our results show that surface mechanisms affect the textural instability of NTB phases in thin planar cells. The instability can even be removed for special anchoring conditions so that NTB phase aligns at large scale.The second challenge was to lower the NTB temperature range (usually close to 100°C) down to room temperature. We studied binary mixtures of CB7CB, a well-known NTB compound, with various cyanobiphenyl smectogens. This allowed us to lower significantly the range of the NTB phase in the 8CB/CB7CB phase diagram, even to the ambient temperature. Optical, thermal, dielectric and elastic properties of such mixtures have been characterized. We also studied their anchoring properties with various substrates and evidenced anchoring transitions on silanized glass that occurs changing the 8CB concentration. In particular, we succeeded in obtaining a quite rare homeotropic anchoring for the NTB phase., Les cristaux liquides se retrouvent aujourd’hui dans nombreuses applications. La phase cristal liquide la plus connue et la plus utilisée est la phase nématique. En 2011 une nouvelle phase, la phase Nématique Twist Bend (NTB), a été découverte. Très prometteuse pour de futures applications, elle pourrait stimuler le développement d’une nouvelle génération de dispositifs électro-optiques. Deux problèmes principaux limitent cependant son utilisation. La phase NTB est difficile à orienter sur de grandes surfaces. Un second défi réside dans l’obtention d’une phase NTB stable à température ambiante. Les travaux de cette thèse sont focalisés sur ces deux problématiques.La mauvaise orientation de la phase NTB dans des cellules planaires se traduit par des textures inhabituelles telles que des textures périodiques de type rayures. Pour comprendre l’origine de ces textures nous avons varié la nature et les paramètres (force d’ancrage, pretilt…) des couches d’alignement. Ce travail nous a permis de mettre en évidence et expliquer le rôle de mécanismes de surface modulant les déformations mais également de proposer des ancrages permettant une bonne orientation de la phase NTB sur de grandes échelles.Le second défi a consisté à abaisser la plage de température d’existence de la phase NTB (d’ordinaire voisine de 100°C) jusqu’à l’ambiante. Pour cela, nous avons étudié des mélanges binaires de CB7CB, un composé NTB très utilisé, et de différents smectogènes de type cyanobiphényle. Le diagramme de phase du mélange binaire 8CB/ CB7CB a montré une baisse très forte de la température de transition N/NTB. Certains mélanges sont stables à 25°C ce qui nous a permis de caractériser en détail leurs propriétés optiques, thermiques, diélectriques et élastiques. Les propriétés d’ancrage sont également modifiées fortement par l'ajout de 8CB au CB7CB. Il est ainsi possible d’obtenir facilement un alignement homéotrope d’une phase NTB, habituellement rare et compliqué à obtenir.

International audience; Prepeak 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 Society

Nematic twist-bend phases (NTB) are new types of nematic liquid crystalline phases with attractive properties for future electro-optic applications. However, most of these states are monotropic or are stable only in a narrow high temperature range. They are often destabilized under moderate cooling, and only a few single compounds have shown to give room temperature NTB phases. Mixtures of twist-bend nematic liquid crystals with simple nematogens have shown to strongly lower the nematic to NTB phase transition temperature. Here, we examined the behaviour of new types of mixtures with the dimeric liquid crystal [4&prime, 4&prime, (heptane-1,7-diyl)bis(([1&prime, 1&Prime, biphenyl]4&Prime, carbo-nitrile))] (CB7CB). This now well-known twist-bend nematic liquid crystal presents a nematic twist-bend phase below T &asymp, 104 &deg, C. Mixtures with other monomeric alkyl or alkoxy -biphenylcarbonitriles liquid crystals that display a smectic A (SmA) phase also strongly reduce this temperature. The most interesting smectogen is 4&prime, Octyl-4-biphenylcarbonitrile (8CB), for which a long-term metastable NTB phase is found at room and lower temperatures. This paper presents the complete phase diagram of the corresponding binary system and a detailed investigation of its thermal, optical, dielectric, and elastic properties.

International audience; In this work, we have reported the vapor liquid equilibria (VLE) data for the binary mixtures containing {2-(2-ethoxyethoxy)ethanol (1) + 1-propanol, 2-propanol, 1-butanol, or 2-butanol (2)}. All the VLE measurements were conducted at temperatures ranging between (273.15 to 363.15) K over the whole composition range. The NRTL and UNIQUAC models were used to correlate the VLE experimental data. Furthermore, experimental measurements of densities, sound velocities, and refractive indices were measured for aforementioned binary mixtures at atmospheric pressure and at T = (293.15, 303.15, 313.15, and 323.15) K. By utilizing the experimental results, the excess/deviation functions were calculated and fitted to the Redlich–Kister polynomial equation.

The work presented in this thesis is a contribution to the study of natural thermosolutal convection in rectangular configurations confining binary mixtures. Couplings of second order (Soret effect or thermo-diffusion and Dufour effect or diffusion-thermo), often neglected in the literature, were considered in addition to an internal volumetric heat generation. The use of numerical simulation methods different from conventional methods was among the objectives of this study. Thus, we have adopted the lattice Boltzmann method which is a mesoscopic approach with a simple (SRT) and multiple (MRT) relaxation time approximations. The study was focused on the effect of the least studied parameters in the literature (intensity of internal heat generation, Soret effect and Dufour effect) in the case of thermal and solutal buoyancy forces with the same intensity and opposite or cooperating effects. The results obtained are characterized by a wealth of phenomena generated by the combined effects of the control parameters and not reported in the literature. For example, the possibility of purification/loading of the medium from/with species by Soret effect was observed depending on the other control parameters. The study has also allowed to identify the stabilizing and destabilizing effects of the Soret and Dufour parameters on the intensities ranges of the internal heat generation that lead to steady and unsteady flows in the absence of the effects of the thermo-diffusion and diffusion-thermo, Le travail présenté dans cette thèse est une contribution à l'étude de la convection naturelle thermosolutale dans des configurations rectangulaires confinant des mélanges binaires. Des couplages de second ordre (effet Soret ou thermo-diffusion et effet Dufour ou diffusion-thermo), souvent négligés dans la littérature, ont été considérés en plus d'une génération volumique interne de la chaleur. Le recours à des méthodes numériques de simulation différentes des méthodes classiques faisait partie des objectifs de cette étude. Ainsi, on a adopté la méthode de lattice Boltzmann sur réseau qui est une approche mésoscopique avec une approximation à temps de relaxation simple (SRT) et multiple (MRT). L'étude a été focalisée sur l'effet des paramètres les moins étudiés dans la littérature (intensité de la génération interne de la chaleur, effet Soret et effet Dufour) pour des forces de volumes thermique et solutale de même intensité avec des effets opposés ou coopérants. Les résultats obtenus sont caractérisés par une richesse de phénomènes engendrés par les effets combinés des paramètres de contrôle et non reportées dans la littérature. Par exemple, la possibilité de purification/charge du milieu des/en espèces par effet Soret a été observée dépendamment des autres paramètres de contrôle. L'étude a permis également d'identifier des effets stabilisants et déstabilisants des paramètres de Soret et Dufour sur les gammes des intensités de la génération interne de la chaleur qui conduisent à des écoulements stationnaires et instationnaires en l'absence des effets de la thermo-diffusion et de la diffusion-thermo

The analysis of different types of structuring, present in simple and complex liquids and their mixtures, was done using the method of molecular dynamics. Complex mixtures have at least one associative component, such as water, alcohols (mono-ols and diols) and amines. The supra-molecular structuring in these mixtures is detected, described, quantified and connected with the atom-atom interactions is the molecules. These systems have interesting fluctuation behaviors, as shown through Kirkwood-Buff integrals. Their correlation functions behave in a complex way, depending on the component, concentration and temperature. The pre-peak at small k values in the site-site structure factor is defined as a signature of molecular domains in these mixtures. A special focus is placed on long-range structuring, which is a novelty considering the majority of the work in the field of the physics of liquids. This thesis contributes to a better understanding of micro-heterogeneous structures in molecular liquids, and gives new links to structural heterogeneities in soft and bio-matter., L'analyse de différents types de structuration, présents dans des liquides simples et complexes et leurs mélanges, a été réalisée en utilisant la méthode de la dynamique moléculaire. Les mélanges complexes ont au moins un composant associatif, tel que l'eau, les alcools (mono-ols et diols) et les amines. La structuration supra-moléculaire dans ces mélanges est détectée, décrite, quantifiée et liée aux interactions atome-atome entre les molécules. Ces systèmes ont des fluctuations aux comportements intéressants, comme le montrent les intégrales de Kirkwood-Buff. Leurs fonctions de corrélation se comportent d'une manière complexe, en fonction du composant, de la concentration et de la température. Le pré-pic aux petites valeurs de k dans les facteurs de structure site-site est défini comme une signature de la ségrégation en domaines dans ces mélanges. Une attention particulière est mise sur la structuration à longue portée, ce qui est une nouveauté compte tenu de la majorité des travaux dans le domaine de la physique des liquides. Cette thèse contribue à une meilleure compréhension des structures micro-hétérogènes dans les liquides moléculaires et permet d'établir des liens avec les hétérogénéités structurelles dans la matière molle et de la bio-matière.

This article belongs to the Proceedings of Eurosensors 2018 (Graz, Austria, 9-12 sept. 2018); International audience; In this work, we study the effect of nanostructured octahedral SnO2 added with a binary mixture p-type and n-type metal oxide semiconductors of CuO and ZnO, on CO detection at two concentrations (100 ppm and 1000 ppm). These metal oxides (SnO2 and binary mixture of CuO75%/ZnO25%) are prepared in the form of a serigraphy paste and deposited on an optimized silicon micro-hotplate. The sensors can be operated at temperature of 550 °C with a low energy consumption of only 55 mW. The binary and ternary mixtures of metal oxide are operated at different working temperature to optimize their sensitivity to CO.

International audience; The aim of the research was to evaluate the influence of certain components of paper such as lignin and papermaking additives (fillers and sizing) on the efficiency of a recently proposed treatment for simultaneous deacidification and mechanical strengthening with polyaminosiloxane copolymer networks. Mixed mechanical and chemical pulp papers containing various additives were treated with aminoalkylalkoxysilanes (AAAS) by immersion or by spray. Upon treatment, the deposited alkaline reserve varied from 0.34 to 1.14 mol kg −1 . For all the papers, copolymers formed from binary mixtures of a di- and a tri-functional AAAS provided the best improvement in the mechanical properties, i.e. in the tensile strength and the folding endurance, indicating an increase in the interfiber bonding energy and in the paper flexibility and plasticity, respectively. It was found that fillers had no influence while sizing hampered the efficiency of the treatment. The presence of mechanical pulp was shown to have a significant impact on the effect of the treatments as well by increasing the tensile resistance more than the folding endurance, indicating an increase in the paper rigidity. This observation was attributed to the response of lignin to the treatment.

International audience; In the scope of improving the energy and power densities of electrochemical double layer capacitors (EDLCs), the development of high performance electrolytes with enhanced operative voltages is imperative. The formulation of mixtures containing ionic liquids with organic molecular solvents is an important strategy in the pursuit of developing highly electrochemically stable and safe materials while retaining fast transport properties for high power applications. In this work, we report on the physical–chemical investigations into binary mixtures containing the ionic liquid 1-butyl-1-methylpyrrolidinium bis{(trifluoromethyl)sulfonyl}imide with one mononitrile solvent, butyronitrile, and two dinitrile solvents, glutaronitrile and adiponitrile, as potential electrolytes for EDLCs. The thermal, volumetric, and transport properties of the binary mixtures are investigated as functions of the electrolyte composition and temperature. Furthermore, the electrolyte composition which exhibits the highest conductivity for each of the binary mixtures was determined, and its electrochemical stability is reported using a glassy carbon macrodisk electrode.

International audience; Transient behavior of the heat transfer through binary gas mixture, confined between two infinite parallel plates, caused by the sudden change of the plates' temperatures, is studied for two monoatomic gas mixtures: Ne-Ar and He-Ar. The walls' temperature changes are considered small compared to the equilibrium temperature of the system, so the McCormack kinetic model is used for the numerical simulations. The time evolution of the main macroscopic parameter is investigated for various species concentrations and for different gas rarefactions ranging from near the free molecular to slip flow regime. It is found that the mixture heat flux takes several characteristic times, which is defined by the distance between the plates over the most probable molecular speed, to achieve its new equilibrium state. This time of the steady state flow establishment depends strongly on the gas rarefaction, mixture nature and composition. (C) 2016 Elsevier Ltd. All rights reserved.

In this work, the parameters and mechanisms governing the reactivity of cerium based materials towards the degradation of textile dyes, taken separately or in binary mixture, in Fenton/photo-Fenton process have been investigated. For this purpose, five sets of catalysts were performed in order to determine the respective effects of : (i) the specific surface area of commercial CeO2 (SBET = 11, 101,5 ; 148 ; 235 and 284 m2/g); (ii) the zirconia doping ((CexZr1-xO2 with different Ce content (x = 0 ; 0,2 ; 0,5 ; 0,8 ; 1)); (iii) the treatment with H2SO4 ; and (iv) the impregnation of different metals in CeO2 (M = Ba, Bi, La, V and Mo). The textural, structural and chemical properties of the studied ceria-based materials were systematically characterized by nitrogen porosimetry, Raman, XRD, XPS, ATR/FTIR, DR-UV-Vis and TGA. Discoloration and mineralization kinetics of Orange II dye in presence of CeO2/H2O2 system are strongly related to the surface area of catalysts and other parameters (UV-Vis irradiation, pH, temperature, concentration of catalyst and H2O2). The presence of another dye with similar (Acid Green 25) or opposite charge (Malachite Green) can also influence the discoloration kinetics of Orange II. Comparing with single dye solutions, the degradation efficiency of both Orange II and Acid Green 25 were reduced in the mixture due to the competitive adsorption of both anionic dyes onto the same surface Ce sites. However, the discoloration of Malachite Green was enhanced in the presence of Orange II due to the simultaneous contribution of both coagulation/flocculation and Fenton-like process. It is suggested that a Malachite Green ion is electrostatically attracted by an Orange II ion at pH = 3. In addition, the performance of the mixed oxides in the heterogeneous Fenton process is strongly related to their textural, structural and chemical properties. Briefly, characterizations by XRD and Raman spectroscopy indicate that these nanosized mixed oxides can be considered as good quality solid solutions and possess structural properties consistent with the known phase diagram of CexZ1-xO2. The sulfation treatment mostly affects the Ce rich catalysts by increasing the crystallite size and lowering the specific surface area. The dissolution of ceria during sulfation followed by formation of Ce(SO4)2 amorphous phase on catalyst surface was investigated by UV-Vis and TGA analysis. Sulfation treatment as well as doping ceria with Zr increases the amount of reduced sites Ce (III) and defect sites.DR-UV-Vis, FTIR/ATR and Raman spectroscopic studies for adsorption and activation of H2O2 on mixed oxides show the formation of surface Ce-peroxo species as intermediate to generate hydroxyl radicals. The relative amounts of these species on the mixed oxides and/or not modified was indirectly determined using TPD-MS, giving rather good indication about the performances of catalysts towards the degradation of dye. The concentration of surface Ce, the density of defects Ce(III) sites (increased by doping and sulfation treatment) and the surface area appear to be among the most important parameters affecting the catalytic activity. Impregnation of ceria with different metals did not show a positive effect on the reactivity of this material in Fenton process. A possible mechanism for the activation of H2O2 was discussed in details according to all the experimental results and to the literature. From a mechanistic viewpoint, it is shown using FTIR/ATR and liquid UV-Vis spectroscopic measurements that the adsorption of the anionic dye is highly pH-dependent and proceeds via electrostatic interactions with surface metal centers. A possible pathway for Orange degradation is proposed on the basis of qualitative and quantitative detection of intermediate compounds, in liquid phase and on catalyst surface, using various techniques (FTIR/ATR, DR-UV-VIS, HPLC and GC/MS), Dans cette étude nous avons cherché à évaluer les paramètres et les mécanismes gouvernant la réactivité des catalyseurs à base de cérium lors de la dégradation des colorants textiles, seuls ou en mélange binaire, dans le cadre du procédé Fenton/photo-Fenton. Dans ce but, 5 séries de catalyseurs à base de cérium ont été testées pour déterminer les effets respectifs : (i) de la surface spécifique de CeO2 commercial (SBET = 11, 101,5 ; 148 ; 235 et 284 m2/g), (ii) du dopage au zirconium (oxydes mixtes CexZr1-xO2 avec différentes teneurs en cérium (x = 0 ; 0,2 ; 0,5 ; 0,8 ; 1)), (iii) d’un traitement de sulfatation de CexZr1-xO2 par H2SO4, et (iv) de l’imprégnation de CeO2 par différents métaux (M = Ba, Bi, La, V et Mo). Les propriétés texturales, structurales et chimiques des catalyseurs à base de cérium étudiés ont été dans la plupart des cas caractérisées par porosimétrie à l’azote, DRX, Raman, XPS, FTIR/ATR, DR-UV-Vis et ATG. Les cinétiques de décoloration et de minéralisation de l’Orange II en présence de CeO2 et H2O2 dépendent fortement de la surface spécifique des catalyseurs ainsi que des paramètres opératoires (présence d’irradiation UV-Vis, pH, température, concentration initiale en catalyseur et en H2O2). Par comparaison avec les colorants pris séparément, l’adsorption compétitive de l’Orange II et de l’Acide Vert 25 sur les mêmes sites d’adsorption à pH = 3 réduit les taux de dégradation des deux colorants en mélange. En revanche, l’association de l’Orange et du Vert de Malachite en paires d’ion, permet d’améliorer la cinétique apparente de dégradation du Vert de Malachite d’un facteur 5. Dans ce cas, la réaction de Fenton et la coagulation-floculation contribuent simultanément à l’élimination de deux colorants de charge opposée en présence du système CeO2/H2O2. De plus, les performances des oxydes mixtes Ce-Zr dans le procédé Fenton hétérogène sont étroitement liées à leurs caractéristiques texturales, structurales et chimiques. Les analyses effectuées ont permis de vérifier les phases cristallines des oxydes mixtes de révéler la formation de solutions solides. Le traitement de sulfatation conduit à la diminution de la surface spécifique et l’augmentation de la taille des cristallites des oxydes riches en Ce. La dissolution de CeO2 lors de sulfatation suivie par formation d’une phase amorphe Ce(SO4)2 à la surface du catalyseur a été mise en évidence. Le traitement de sulfatation ainsi que le dopage au Zr permettent d’augmenter la densité de surface en sites réduits Ce(III). Les études en spectroscopies DR-UV-Vis, FTIR/ATR et Raman relatives à l’adsorption et l’activation d’H2O2 par les oxydes mixtes ont permis de mettre en évidence l’existence d’espèces Ce-peroxo de surface, comme intermédiaires pour générer les radicaux hydroxyles. La détermination quantitative de ces espèces par TPD-MS s’est avérée utile pour mieux comprendre les performances catalytiques des oxydes mixtes modifiés ou non. La concentration en Ce de surface, la densité de défauts Ce(III) (augmenté par dopage et le traitement de sulfatation) et la surface spécifique semblent être à cet égard parmi les paramètres les plus influents sur l’activité. L’imprégnation de CeO2 par différents métaux n’a pas montré un impact positif sur la réactivité de ce matériau en procédé Fenton. Un mécanisme général d’activation d’H2O2 a été proposé sur la base des résultats expérimentaux obtenus et la littérature. De point de vue mécanistique, les analyses spectroscopiques par ATR/FTIR et UV-Vis montrent que l’adsorption de l’Orange II à la surface du catalyseur est fortement dépendante du pH du milieu et se fait par des interactions électrostatiques. Le mécanisme de dégradation de l’Orange II, en phase liquide et à la surface du catalyseur, a été étudié par différentes techniques (DR-UV-VIS et ATR/IR, HPLC et GC/MS)

In this work, the parameters and mechanisms governing the reactivity of cerium based materials towards the degradation of textile dyes, taken separately or in binary mixture, in Fenton/photo-Fenton process have been investigated. For this purpose, five sets of catalysts were performed in order to determine the respective effects of : (i) the specific surface area of commercial CeO2 (SBET = 11, 101,5 ; 148 ; 235 and 284 m2/g); (ii) the zirconia doping ((CexZr1-xO2 with different Ce content (x = 0 ; 0,2 ; 0,5 ; 0,8 ; 1)); (iii) the treatment with H2SO4 ; and (iv) the impregnation of different metals in CeO2 (M = Ba, Bi, La, V and Mo). The textural, structural and chemical properties of the studied ceria-based materials were systematically characterized by nitrogen porosimetry, Raman, XRD, XPS, ATR/FTIR, DR-UV-Vis and TGA. Discoloration and mineralization kinetics of Orange II dye in presence of CeO2/H2O2 system are strongly related to the surface area of catalysts and other parameters (UV-Vis irradiation, pH, temperature, concentration of catalyst and H2O2). The presence of another dye with similar (Acid Green 25) or opposite charge (Malachite Green) can also influence the discoloration kinetics of Orange II. Comparing with single dye solutions, the degradation efficiency of both Orange II and Acid Green 25 were reduced in the mixture due to the competitive adsorption of both anionic dyes onto the same surface Ce sites. However, the discoloration of Malachite Green was enhanced in the presence of Orange II due to the simultaneous contribution of both coagulation/flocculation and Fenton-like process. It is suggested that a Malachite Green ion is electrostatically attracted by an Orange II ion at pH = 3. In addition, the performance of the mixed oxides in the heterogeneous Fenton process is strongly related to their textural, structural and chemical properties. Briefly, characterizations by XRD and Raman spectroscopy indicate that these nanosized mixed oxides can be considered as good quality solid solutions and possess structural properties consistent with the known phase diagram of CexZ1-xO2. The sulfation treatment mostly affects the Ce rich catalysts by increasing the crystallite size and lowering the specific surface area. The dissolution of ceria during sulfation followed by formation of Ce(SO4)2 amorphous phase on catalyst surface was investigated by UV-Vis and TGA analysis. Sulfation treatment as well as doping ceria with Zr increases the amount of reduced sites Ce (III) and defect sites.DR-UV-Vis, FTIR/ATR and Raman spectroscopic studies for adsorption and activation of H2O2 on mixed oxides show the formation of surface Ce-peroxo species as intermediate to generate hydroxyl radicals. The relative amounts of these species on the mixed oxides and/or not modified was indirectly determined using TPD-MS, giving rather good indication about the performances of catalysts towards the degradation of dye. The concentration of surface Ce, the density of defects Ce(III) sites (increased by doping and sulfation treatment) and the surface area appear to be among the most important parameters affecting the catalytic activity. Impregnation of ceria with different metals did not show a positive effect on the reactivity of this material in Fenton process. A possible mechanism for the activation of H2O2 was discussed in details according to all the experimental results and to the literature. From a mechanistic viewpoint, it is shown using FTIR/ATR and liquid UV-Vis spectroscopic measurements that the adsorption of the anionic dye is highly pH-dependent and proceeds via electrostatic interactions with surface metal centers. A possible pathway for Orange degradation is proposed on the basis of qualitative and quantitative detection of intermediate compounds, in liquid phase and on catalyst surface, using various techniques (FTIR/ATR, DR-UV-VIS, HPLC and GC/MS), Dans cette étude nous avons cherché à évaluer les paramètres et les mécanismes gouvernant la réactivité des catalyseurs à base de cérium lors de la dégradation des colorants textiles, seuls ou en mélange binaire, dans le cadre du procédé Fenton/photo-Fenton. Dans ce but, 5 séries de catalyseurs à base de cérium ont été testées pour déterminer les effets respectifs : (i) de la surface spécifique de CeO2 commercial (SBET = 11, 101,5 ; 148 ; 235 et 284 m2/g), (ii) du dopage au zirconium (oxydes mixtes CexZr1-xO2 avec différentes teneurs en cérium (x = 0 ; 0,2 ; 0,5 ; 0,8 ; 1)), (iii) d’un traitement de sulfatation de CexZr1-xO2 par H2SO4, et (iv) de l’imprégnation de CeO2 par différents métaux (M = Ba, Bi, La, V et Mo). Les propriétés texturales, structurales et chimiques des catalyseurs à base de cérium étudiés ont été dans la plupart des cas caractérisées par porosimétrie à l’azote, DRX, Raman, XPS, FTIR/ATR, DR-UV-Vis et ATG. Les cinétiques de décoloration et de minéralisation de l’Orange II en présence de CeO2 et H2O2 dépendent fortement de la surface spécifique des catalyseurs ainsi que des paramètres opératoires (présence d’irradiation UV-Vis, pH, température, concentration initiale en catalyseur et en H2O2). Par comparaison avec les colorants pris séparément, l’adsorption compétitive de l’Orange II et de l’Acide Vert 25 sur les mêmes sites d’adsorption à pH = 3 réduit les taux de dégradation des deux colorants en mélange. En revanche, l’association de l’Orange et du Vert de Malachite en paires d’ion, permet d’améliorer la cinétique apparente de dégradation du Vert de Malachite d’un facteur 5. Dans ce cas, la réaction de Fenton et la coagulation-floculation contribuent simultanément à l’élimination de deux colorants de charge opposée en présence du système CeO2/H2O2. De plus, les performances des oxydes mixtes Ce-Zr dans le procédé Fenton hétérogène sont étroitement liées à leurs caractéristiques texturales, structurales et chimiques. Les analyses effectuées ont permis de vérifier les phases cristallines des oxydes mixtes de révéler la formation de solutions solides. Le traitement de sulfatation conduit à la diminution de la surface spécifique et l’augmentation de la taille des cristallites des oxydes riches en Ce. La dissolution de CeO2 lors de sulfatation suivie par formation d’une phase amorphe Ce(SO4)2 à la surface du catalyseur a été mise en évidence. Le traitement de sulfatation ainsi que le dopage au Zr permettent d’augmenter la densité de surface en sites réduits Ce(III). Les études en spectroscopies DR-UV-Vis, FTIR/ATR et Raman relatives à l’adsorption et l’activation d’H2O2 par les oxydes mixtes ont permis de mettre en évidence l’existence d’espèces Ce-peroxo de surface, comme intermédiaires pour générer les radicaux hydroxyles. La détermination quantitative de ces espèces par TPD-MS s’est avérée utile pour mieux comprendre les performances catalytiques des oxydes mixtes modifiés ou non. La concentration en Ce de surface, la densité de défauts Ce(III) (augmenté par dopage et le traitement de sulfatation) et la surface spécifique semblent être à cet égard parmi les paramètres les plus influents sur l’activité. L’imprégnation de CeO2 par différents métaux n’a pas montré un impact positif sur la réactivité de ce matériau en procédé Fenton. Un mécanisme général d’activation d’H2O2 a été proposé sur la base des résultats expérimentaux obtenus et la littérature. De point de vue mécanistique, les analyses spectroscopiques par ATR/FTIR et UV-Vis montrent que l’adsorption de l’Orange II à la surface du catalyseur est fortement dépendante du pH du milieu et se fait par des interactions électrostatiques. Le mécanisme de dégradation de l’Orange II, en phase liquide et à la surface du catalyseur, a été étudié par différentes techniques (DR-UV-VIS et ATR/IR, HPLC et GC/MS)

Phase transitions near a critical point, or second order phase transitions, are still a recent object of studies because of the large amount of interesting critical phenomena as the critical Casimir force, confinements problems or out of equilibrium phenomena following a quench at the critical point. This thesis experimentally studies phenomena near a critical point.This manuscript is divided in two parts : the first one consists in building several experimental set-up which measure viscosity through thermal fluctuation at micrometric scale. The second part consists in finding and characterize binary mixtures which show a second order phase transition. Preliminary results have been done in these samples. One of the principal points of these experimental set-up are a well regulated temperature, a probe sensitive to thermal fluctuation and/or pN forces and a reproducible binary mixture which presents a critical point easy to reach experimentally.We mounted from an Atomic Force Microscope (AFM) already built in the laboratory, a hanging-fiber probe to measure viscosity of liquids. Despite its weak efficiency as a metrologic probe, we described and developed a mode coupling model which let us understand mechanics of hanging-fiber probes. I also developed in the lab the dynamic differential microscopy technique (DDM) which do measurements with several probes. I discussed about the measure precision with in mind the aim of studying critical fluctuations.For the choice of the sample, we studied several binary mixtures. We characterized them by classical methods as turbidity measurements and static light scattering. These characterizations let us learn about binary mixtures in order to use them in a third experimental set-up : beads trapped in an optical tweezers already built in the lab. We added to it a home-made thermal regulation which can be used with the constraints of optical tweezers. These tests showed an unexpected phenomenon of oscillating phase transition induce by laser. We developed a model to describe it. At last, preliminary experiments with optical tweezers in binary mixtures showed qualitative effects of an approach near a critical point on the viscosity and on interactions between beads as critical Casimir force., Les transitions de phase près d'un point critique - dites du second ordre - sont un sujet toujours d'actualité en raison des nombreux phénomènes critiques intéressants tels que la force de Casimir critique, les problèmes de confinements ou les phénomènes hors d'équilibre suivant une trempe au point critique. Cette thèse vise à étudier expérimentalement certains phénomènes engendrés près d'un point critique. La thèse est divisée en deux axes : le premier consiste à développer plusieurs systèmes expérimentaux qui permettront de mesurer essentiellement la viscosité, par l'intermédiaire des fluctuations thermiques à l'échelle micrométrique. Le deuxième axe consiste à trouver et caractériser des mélanges binaires présentant une transition de phase du second ordre dans lesquelles on souhaite faire des mesures. Les enjeux de ces systèmes expérimentaux sont d'avoir une régulation en température précise, une sonde de mesure sensible aux fluctuations thermiques et/ou à des forces de l'ordre du pN, et un échantillon fiable et reproductible présentant un point critique accessible expérimentalement. Nous avons ainsi monté à partir d'un microscope à force atomique (AFM) déjà présent au laboratoire, un système de mesure de viscosité à sonde AFM fibrée. Malgré sa faible efficacité en terme de sonde de mesure métrologique, nous avons pu décrire et développer un modèle de couplage de modes de vibration permettant de comprendre la mécanique de microleviers AFM fibrés. J'ai également développé au laboratoire la mesure de microscopie dynamique différentielle qui permet de faire des mesures à sondes multiples contrairement au premier montage. J'ai discuté de la précision de la mesure dans le cadre de notre objectif d'étude des fluctuations critiques.En ce qui concerne l'échantillon de mesure, nous avons étudié plusieurs mélanges binaires que nous avons caractérisés par des méthodes classiques de turbidité et diffusion statique de la lumière. Cette caractérisation nous a permis de connaître les mélanges binaires pour les utiliser dans un troisième système de mesure : billes micrométriques piégées dans des pinces optiques déjà monté au laboratoire. Nous y avons rajouté un système de régulation thermique fait maison pour être exploité avec les contraintes de la pince optique. Ces tests ont fait apparaître un phénomène inattendu d'oscillations de transition de phase induites par laser. Nous avons développé un modèle pour les décrire. Enfin, des expériences préliminaires - toujours avec les pinces optiques dans les mélanges binaires - nous ont permis d'observer qualitativement des effets de l'approche au point critique par des mesures de viscosité et d'interaction type force de Casimir critique.

Phase transitions near a critical point, or second order phase transitions, are still a recent object of studies because of the large amount of interesting critical phenomena as the critical Casimir force, confinements problems or out of equilibrium phenomena following a quench at the critical point. This thesis experimentally studies phenomena near a critical point.This manuscript is divided in two parts : the first one consists in building several experimental set-up which measure viscosity through thermal fluctuation at micrometric scale. The second part consists in finding and characterize binary mixtures which show a second order phase transition. Preliminary results have been done in these samples. One of the principal points of these experimental set-up are a well regulated temperature, a probe sensitive to thermal fluctuation and/or pN forces and a reproducible binary mixture which presents a critical point easy to reach experimentally.We mounted from an Atomic Force Microscope (AFM) already built in the laboratory, a hanging-fiber probe to measure viscosity of liquids. Despite its weak efficiency as a metrologic probe, we described and developed a mode coupling model which let us understand mechanics of hanging-fiber probes. I also developed in the lab the dynamic differential microscopy technique (DDM) which do measurements with several probes. I discussed about the measure precision with in mind the aim of studying critical fluctuations.For the choice of the sample, we studied several binary mixtures. We characterized them by classical methods as turbidity measurements and static light scattering. These characterizations let us learn about binary mixtures in order to use them in a third experimental set-up : beads trapped in an optical tweezers already built in the lab. We added to it a home-made thermal regulation which can be used with the constraints of optical tweezers. These tests showed an unexpected phenomenon of oscillating phase transition induce by laser. We developed a model to describe it. At last, preliminary experiments with optical tweezers in binary mixtures showed qualitative effects of an approach near a critical point on the viscosity and on interactions between beads as critical Casimir force.; Les transitions de phase près d'un point critique - dites du second ordre - sont un sujet toujours d'actualité en raison des nombreux phénomènes critiques intéressants tels que la force de Casimir critique, les problèmes de confinements ou les phénomènes hors d'équilibre suivant une trempe au point critique. Cette thèse vise à étudier expérimentalement certains phénomènes engendrés près d'un point critique. La thèse est divisée en deux axes : le premier consiste à développer plusieurs systèmes expérimentaux qui permettront de mesurer essentiellement la viscosité, par l'intermédiaire des fluctuations thermiques à l'échelle micrométrique. Le deuxième axe consiste à trouver et caractériser des mélanges binaires présentant une transition de phase du second ordre dans lesquelles on souhaite faire des mesures. Les enjeux de ces systèmes expérimentaux sont d'avoir une régulation en température précise, une sonde de mesure sensible aux fluctuations thermiques et/ou à des forces de l'ordre du pN, et un échantillon fiable et reproductible présentant un point critique accessible expérimentalement. Nous avons ainsi monté à partir d'un microscope à force atomique (AFM) déjà présent au laboratoire, un système de mesure de viscosité à sonde AFM fibrée. Malgré sa faible efficacité en terme de sonde de mesure métrologique, nous avons pu décrire et développer un modèle de couplage de modes de vibration permettant de comprendre la mécanique de microleviers AFM fibrés. J'ai également développé au laboratoire la mesure de microscopie dynamique différentielle qui permet de faire des mesures à sondes multiples contrairement au premier montage. J'ai discuté de la précision de la mesure dans le cadre de notre objectif d'étude des fluctuations critiques.En ce qui concerne l'échantillon de mesure, nous avons étudié plusieurs mélanges binaires que nous avons caractérisés par des méthodes classiques de turbidité et diffusion statique de la lumière. Cette caractérisation nous a permis de connaître les mélanges binaires pour les utiliser dans un troisième système de mesure : billes micrométriques piégées dans des pinces optiques déjà monté au laboratoire. Nous y avons rajouté un système de régulation thermique fait maison pour être exploité avec les contraintes de la pince optique. Ces tests ont fait apparaître un phénomène inattendu d'oscillations de transition de phase induites par laser. Nous avons développé un modèle pour les décrire. Enfin, des expériences préliminaires - toujours avec les pinces optiques dans les mélanges binaires - nous ont permis d'observer qualitativement des effets de l'approche au point critique par des mesures de viscosité et d'interaction type force de Casimir critique.

International audience; Underground coal bed reservoirs naturally contain methane which can be produced. In parallel of the production of this methane, carbon dioxide can be injected, either to enhance the production of methane, or to have this carbon dioxide stored over geological periods of time. As a prerequisite to any simulation of an Enhanced Coal Bed Methane recovery process (ECBM), we need state equations to model the behavior of the seam when cleats are saturated with a miscible mixture of CH4 and CO2. This paper presents a poromechanical model of coal seams exposed to such binary mixtures filling both the cleats in the seam and the porosity of the coal matrix. This model is an extension of a previous work which dealt with pure fluid. Special care is dedicated to keep the model consistent thermodynamically. The model is fully calibrated with a mix of experimental data and numerical data from molecular simulations. Predicting variations of porosity or permeability requires only calibration based on swelling data. With the calibrated state equations, we predict numerically how porosity, permeability, and adsorbed amounts of fluid vary in a representative volume element of coal seam in isochoric or oedometric conditions, as a function of the pressure and of the composition of the fluid in the cleats.

International audience; In this paper, we have reported the CO2 solubility in different pure alkyl carbonate solvents (EC, DMC, EMC, DEC) and their binary mixtures as EC/DMC, EC/EMC, and EC/DEC and for electrolytes [solvent + lithium salt] LiX (X = LiPF6, LiTFSI, or LiFAP) as a function of the temperature and salt concentration. To understand the parameters that influence the structure of the solvents and their ability to dissolve CO2, through the addition of a salt, we first analyzed the viscosities of EC/DMC + LiX mixtures by means of a modified Jones–Dole equation. The results were discussed considering the order or disorder introduced by the salt into the solvent organization and ion solvation sphere by calculating the effective solute ion radius, rs. On the basis of these results, the analysis of the CO2 solubility variations with the salt addition was then evaluated and discussed by determining specific ion parameters Hi by using the Setchenov coefficients in solution. This study showed that the CO2 solubility has been affected by the shape, charge density, and size of the ions, which influence the structuring of the solvents through the addition of a salt and the type of solvation of the ions.

The prediction of interfacial tension of fluids is critical for many industrial applications. Advances in molecular simulation, and the recent evolution of supercomputing calculations allow for some years to predict the values of interfacial tension for complex systems. A work involving liquid / vapor equilibrium of pure compounds SO2, O2, N2 and Ar show that the models used can impact the quality of the prediction. Simulations of acid gas / alkane equilibrium such CO2 / n-butane, CO2 / n-decane or H2S / n-pentane were then performed. They have demonstrated the performance of methods of Monte Carlo simulations for the reproduction of interfacial tensions for such system. The study of ternary systems H2O / N2+CH4 and H2O / CO2+H2S has also shown that using molecular dynamics could help the equilibration of the simulated systems. The study of liquid / vapor equilibrias of sodium chloride brines show that certain non-polarizable models perform very well to predict the changes in the interfacial tension with the molarity of salt. The core-shell polarizable models based on the Drude oscillator model chosen did not allow to predict brines densities and the interfacial tensions. Finally, the study of water / alkane equilibria in the presence of salt or methanol showed that the molecular dynamics methods allow to predict quantitatively interfacial tension values for this kinds of interfaces. The effect of alcohol lowering the interfacial tension has been observed : this small surfactant populate the interfacial region at weak concentration., La prédiction de valeurs de tension interfaciale des fluides est capitale dans de nombreuses applications industrielles. Les techniques de simulation moléculaire et l’évolution rapide des moyens de calcul intensif permettent depuis quelques années de prédire des valeurs de tension interfaciale pour des systèmes complexes. Des travaux concernant des équilibres liquide / vapeur des corps purs SO2, O2, N2 et Ar montrent que les modèles choisi pour chaque molécule peuvent influencer la qualité des prédictions de tension interfaciale. Des simulations d’équilibres gaz acide / alcane de type CO2 / n-butane, CO2 / n-décane et H2S / n-pentane ont ensuite été réalisées. Elles ont mis en évidence l’efficacité des méthodes de simulation de type Monte Carlo pour la prédiction des tensions interfaciales pour de tels systèmes. L’étude de systèmes ternaires H2O / N2+CH4 et H2O / CO2+H2S a par ailleurs montré que le recourt à la dynamique moléculaire pouvait faciliter l’équilibration des systèmes simulés, rendant plus efficace la prédiction des tensions interfaciales. L’étude d’équilibres liquide / vapeur de saumures de chlorure de sodium a permis de mettre en évidence l’efficacité de certains potentiels non-polarisables pour la prédiction de l’évolution de la tension interfaciale avec la molarité de sel. Les modèles polarisables de type core-shell choisis ne permettent de prédire ni les masses volumiques, ni les tensions interfaciales. Enfin, l’étude d’équilibres eau / alcane en présence de sel ou de méthanol a montré que les méthodes de dynamique moléculaire permettaient de prédire quantitativement des valeurs de tension interfaciale pour ce type d’interface. L’effet de l’alcool abaissant la tension interfaciale a bien été observé, tout comme son placement préférentiel à l’interface.

International audience; In this paper, new experimental vapour-liquid equilibrium data of the furan + n-hexane and furan + toluene binary systems are reported. The data are determined using the ebulliometric technique. The measured data are used to assess the predictions obtained with molecular simulation, a group contribution polar PC-SAFT model and the COSMO-RS and COSMO-SAC approaches. For this purpose, new force field parameters (needed in MC-simulation) are determined for furans by fitting a limited amount of saturation data. In GC-PPC-SAFT, most of the parameters were adopted from previous studies with exception of the polar moments (dipoles are taken from experimental data). The mixtures phase diagrams are predicted (without binary parameters) at atmospheric pressure using these newly determined parameters as well as those of hexane and toluene determined in earlier studies.The predicted results are consistent with the new experimental data. Nevertheless, for the furan + n-hexane binary system, it appears that a binary interaction parameter is necessary to correctly correlate the data and to satisfactory describe the literature excess enthalpy data.

International audience; It was designed and constructed a new thermogravitational column able to operate at high pressures (up to 50 MPa). This new thermogravitational column is of the cylindrical type with closed ends. It is made of stainless steel. The length of the column is 0.5 m and the gap between its two walls is variable. First, the column was validated at atmospheric pressure by means of measurements of the thermodiffusion coefficient of well-known binary mixtures. Then, this new thermogravitational column was used to measure the thermodiffusion coefficient of the binary mixtures 1,2,3,4-tetrahydronaphtaleneisobutylbenzene, 1,2,3,4-tetrahydronaphtalenen-dodecane, and isobutylbenzenen-dodecane at high pressures and within the pressure range between 0.1 and 20 MPa at a mean temperature of 25 °C. We have found a linear dependence between the thermodiffusion coefficient and the pressure.

International audience; In this work, we study phase equilibria of systems containing acid gases and glycols. The acid gases include carbonyl sulfide (COS), hydrogen sulfide (H 2S), and carbon dioxide (CO 2) while glycols include monoethylene glycol (MEG), diethylene glycol (DEG), and triethylene glycol (TEG). A brief literature survey on the solubility of the acid gases and hydrocarbons in glycols is presented. New experimental solubility data mainly for COS and some limited data for H 2S in glycols from 276 to 333K and at elevated pressures are reported. Experimental measurements have been carried out using the " static-synthetic" method. The reliability and repeatability of the experimental work are demonstrated. The experimental solubility data for COS and glycols, from this work, and those for H 2S and CO 2 from the literature are modeled using the cubic-plus-association (CPA) equation of state (EoS). CPA parameters for pure components and binary systems are reported. Satisfactory correlations have been achieved using temperature-independent interaction parameters. Various modeling strategies and alternatives using CPA are tested and the results are critically evaluated. The variations and trends in the values of binary interaction parameters are discussed for the different systems studied.

International audience; By exploiting the coupling between convection and thermodiffusion, we examine in this study the possibility to perform separation of species in viscoelastic solutions saturating a porous cavity heated from below. We analyze the thermal convection thresholds and linear characteristics of the primary and secondary instabilities for binary mixtures with viscoelastic properties taking into account the Soret effect and the lateral confinement of the medium. We focus on viscoelastic mixtures with positive separation ratio ψ, a dimensionless parameter which represents the mass contribution divided by the temperature contribution to buoyancy forces and is proportional to the strength of the Soret effect. In that case, the lighter component of the viscoelastic solution is driven into the direction of the bottom of the cavity, thus further enhancing the density gradient. We find that for sufficiently elastic mixtures, oscillatory instability may be sustained for small positive ψ contrary to the case of Newtonian mixtures, where oscillatory convection occurs only for ψψmono>0 a stationary bifurcation leads to a monocellular flow at the onset of convection, with a horizontal stratification of the concentration, allowing separation of species between the two ends of the cell. The optimum of separation is obtained for a particular value Raopt of the Rayleigh number. The linear stability analysis of the monocellular flow is performed, and the critical conditions above which the flow becomes unstable are determined. The combined influence of the viscoelastic parameters and the lateral confinement on the characteristics of the secondary instability is quantified as a function of ψ. It is found that, depending on the lateral confinement, the monocellular flow may lose its stability via a Hopf bifurcation giving rise to transversal travelling rolls or via a stationary bifurcation to fixed longitudinal rolls. When the secondary bifurcation is a Hopf one, two regimes of convection are identified. While the viscoelastic mechanism plays a key role in one regime, the other regime is dominated by the Soret effect. Independently of the nature of the secondary instability pattern, it is shown that the monocellular flow remains stable beyond Raopt indicating that optimal separation of species is possible for viscoelastic solutions.

The present study aimed to investigate olfactory anhedonia and olfactory negative alliesthesia in depressed patients. Two odorants, one with pleasant (vanillin), and one with unpleasant (butyric acid) hedonic valence were evaluated by 30 depressed inpatients and 30 controls (healthy subjects, matched by age and gender). Participants explored the hedonic valence, intensity (discrimination) and perceived quality (identification) of 16 different stimuli (3 concentrations of odorants, their 9 combinations, and 1 control containing distilled water). The hedonic perception showed that patients perceived the unpleasant odorant as significantly more unpleasant than controls (olfactory negative alliesthesia). Concerning the intensity ratings, controls were able to discriminate between all concentrations of odorants, while patients discriminated between the different concentrations only for the unpleasant component and not for the vanillin (olfactory anhedonia). Regarding the identification task in an iso-intense unmixed odorants mixture, patients perceived significantly less the pleasant odorant than the unpleasant one (olfactory anhedonia), whereas controls perceived both odorants equally well. These results support the notion of an olfactory perception impairment in depression. Further studies are needed to replicate these findings and to confirm that such olfactory anhedonia or/and olfactory negative alliesthesia could be a state or a trait of depression.

The sewage sludge ash can potentially be used for the removal of metal ions from wastewater due to its similar chemical composition to that of fly ash. The aim of this work was to investigate the adsorptive characteristics of this material including specific surface area and pH of zero point of charge (pHZPC) and to assess the possibility of removing nickel and cadmium from aqueous solutions by this sorbent. The effects of agitation time, pH, initial metal ion concentration and temperature on the removal of these metals were studied. In order to study the sorption isotherm, two equilibrium models, the Langmuir and Freundlich isotherms, were analyzed. The effect of solution pH on the adsorption onto sewage sludge ash was studied in the pH range from 2 to 8. The adsorption was endothermic and the computation of the parameters, ΔH°, ΔS° and ΔG°, indicated that the interactions were thermodynamically favourable. Experiments with Ni and Cd adsorption measured together showed that Cd severely interfered with Ni adsorption to sewage sludge ash and vice versa under the conditions of the two coexisted ions adsorption.

Symposium on Powder Science and Technology - Powders and Sintered Material, Albi, FRANCE, MAY 23-25, 2007; International audience; The compaction behavior of binary mixtures of lactose and a functional excipient containing 98% of microcrystalline cellulose and 2% of silica was investigated by experiment. The densification process and the role of each component in the compaction behavior were examined by analyzing the effect of the composition on the stress transmission to the powder bed in axial (stress transmission) and in radial (stress transfer) directions. Unlike the behavior of a single component where the applied pressure is predominantly transmitted in the axial direction to the powder bed for densification, the increase of the composition of lactose up to 50% in mixtures increases the stress transfer that becomes greater than the stress transmission. However, for the compaction behavior of mixtures with 50% of lactose, two opposite behaviors were found, below and above a pressure around 70 MPa. Die-wall friction showed also a change at this pressure due to a smoothed contact surface with wall. By increasing the composition of lactose (>50%), the behavior of mixtures becomes dominated by the behavior of lactose where the transmission is better than the transfer. This study demonstrates that the analysis of the compaction behavior of mixtures by recording stress transmission, stress transfer and wall friction give pertinent information about the role of each component in the densification and Could be, to a certain extent, help to the selection of excipient for powder formulation.

International audience; Accurate knowledge of phase diagrams is an essential step for optimized chemical engineering design and effective solution of engineering-related problem. As an example of the use of phase diagrams we have selected a topic at global concern which arose upon the discovery of the ozone depletion. In 1987, the Montreal protocol prohibited world-wide use and production of ChloroFluoroCarbons (CFCs) and of HydroChloroFluoroCarbons (HCFCs), while HydroFluoroCarbons (HFCs) were proposed as alternative refrigerants. Thus, the need arose for information required in the optimization of refrigerant production processes, particularly in the field of phase equilibria. These data can provide better evaluation of refrigerant production processes, especially with the aim of reducing global warning effects. In this communication, we present VLE equipments and the obtained phase diagrams concerning several binary systems involving R32, R290, R116, R744, R116, R134a, R227ea and other refrigerants. Cubic equations of state combining with modern mixing rules based on Gibbs excess models are used for the determination of phase diagrams.

International audience; Isothermal vapor - liquid equilibrium data are presented for the system hexafluoroethane (R116) + propane. Measurements were performed for six isotherms (three isotherms below and three above the critical temperature of R1 16) ranging from (263.3 to 323.19) K, with pressure ranging from (0.344 to 3.851) MPa. The measurements were undertaken using a "static-analytic" type apparatus, with sampling of the equilibrium phases via pneumatic capillary samplers (Rolsi, Armine's patent). The apparatus as well as the samplers were developed in the CEP/TEP laboratory. The uncertainties in the measurements were within ± 0.01 K, ± 0.0003 MPa, and < 2.0 % for temperatures, pressures, and mole fractions, respectively. The full set of isothermal vapor - liquid equilibrium data was correlated with the Peng - Robinson equation of state, incorporating the Mathias - Copeman alpha function, with the Wong - Sandler mixing rule utilizing the NRTL activity coefficient model.

International audience; Compressed liquid densities for the 2-propanol (1) + water (2) mixture have been determined at (300, 325, and 350) K and x 1, close to 0.25, 0.49, and 0.73 using a vibrating tube densimeter. Liquid densities have been measured from about atmospheric pressure up to 10 MPa and correlated with a multilayer feedforward neural network. The composition dependence of the excess molar volume has been evaluated in the temperature and pressure range of the experimental data. A model based on a multilayer feedforward neural network function combined with the saturated pressure equation of the pure fluids has been regressed on the available literature data for the bubble pressure. The correlations for liquid density and bubble pressure have been used to generate the saturated liquid density surface in the whole temperature range of the measured compressed liquid densities and for compositions ranging from the pure 2-propanol to the pure water.

International audience; The aim of the paper is to investigate the structure of solutions of microcrystalline cellulose in NaOH/water mixtures and to determine the limit of cellulose solubility. The binary NaOH/water and the ternary cellulose/NaOH/water phase diagrams in the area of cellulose dissolution (7-10% NaOH below 0 °C) are studied by DSC. The NaOH/water binary phase diagram has a simple eutectic behavior. Because of the existence of this eutectic structure, it is possible to measure the influence of the addition of pure low molar mass microcrystalline cellulose. This shows that a minimum of four NaOH molecules should be linked to one anhydroglucose unit to allow for the dissolution of microcrystalline cellulose. The proportions between bound Avicel, NaOH, and water molecules as a function of cellulose concentrations are calculated. A tentative explanation about the origin of the dissolving power of NaOH/water is given.

International audience; There has recently been an increased interest in predicting the tensile strength of binary tablets from the properties of the individual components. In this paper, measurements are reported for tensile strength of tablets compressed from single-component and binary powder mixtures of lactose with microcrystal line cellulose (MCC), and lactose with two types of silicified microcrystalline cellulose (SMCC and SMCC-HD), which are different in compressibility. Measurements show the tensile strength increases with. the relative density for single powders, and both with the relative density and the mass fraction of cellulose in the mixtures. It was also observed, for binary mixtures compacted at 50 and 150MPa, that there was a slight variation in porosity with the mass fraction of celluloses. The predictions of the tensile strength of binary tablets from the characteristics of the single-components was analysed with the extended Ryshkewitch-Duckworth model by assuming both linear and power law mixing rules for the determination of the parameters ``tensile strength at zero porosity and bonding capacity constant''. As consequence, four models were analysed and compared with measurements using criteria based on the standard deviation from the mean values. Results showed a good prediction using a linear mixing rule combined with the power law. However, as the predictions of these models depend on the powders and the porosity range for the characterization of single-components, none of them can be systematically considered as being the best to predict binary behaviour from data for individual powders.

Three pharmaceutical excipients (microcrystalline cellulose, lactose, anhydrous calcium phosphate) and their binary mixtures were compacted to form compacts of various mean porosities. Some mechanical properties (Young's modulus, tensile strength and Brinell hardness) were studied on these compacts. The mechanical properties of the binary mixtures were not proportional to the mixture composition expressed in mass. More, for all the properties, a negative deviation was always observed from this linear relationship. In reference to a composition percolation phenomenon, critical mass fractions were detected from the graph mechanical property vs. mass composition of a mixture. The results obtained with Brinell hardness differed from the results of the Young's modulus and the tensile strength, i.e. the most plastic material in the binary mixture controlled the mixture behaviour. Secondly, a predictive model based on a statistical approach was proposed for the Young's modulus and the tensile strength. The validity of this model was verified on experimental data, and an interaction parameter used to characterize the affinity of the two compounds was calculated. Finally, the X-ray tomography technique was applied to the compacts of cellulose/phosphate mixtures to obtain cross-sections images of the compacts. The analysis of the cross-sections images allowed explaining the no linear relationship of the different mechanical properties results observed on these binary mixtures.

The compressibility of three pharmaceutical excipients (microcrystalline cellulose, lactose and anhydrous calcium phosphate) and their binary mixtures was studied. The aim of this work was to observe the impact of the mass composition of the mixture on the compressibility. The single-compound materials and their mixtures were compacted using instrumented presses. It allowed obtaining compression cycles (i.e., force–displacement curves) which were associated with energy measurements (specific compaction energy, Esp cp and specific expansion energy, Esp exp). It was observed that for the mixtures studied, the change of Esp cp with the mass composition could be fitted using a linear relationship (it was not the case with Esp exp). A linear relationship between the porosity of mixture’s compacts and the mass composition was also obtained. Heckel’s plots were then obtained for the three excipients and the mixtures. The mean yield pressure was calculated with the “in-die-method” and the “out-of-die method”. A proportional relationship was not valid for the mean yield pressures. But, a predictive approach was proposed in order to obtain indirectly the mean yield pressure of a binary mixture if the data of the single materials were known. It used the linear mixing rule observed with the porosity. The validity was verified and compared with the experimental values. This comparison showed that it was possible to predict the mean yield pressure of binary mixtures from the accessible data of the single excipients.

The tablet remains the dosage form the most present on the market. These tablets are obtained by the compaction of complex mixtures of an active substance and some excipients.The aim of this work was to evaluate the behaviour of various binary mixtures of three pharmaceutical excipients.The first part of this work is about the study of the compressibility and the compactibility of the excipients alone. Tests of characterization of the solid fraction by microtomography X supplemented this study.The second part deals with the study of the variation of compressibility and mechanical properties when the binary mixture composition changes. Microtomography X were also carried out on one of the mixture.This work was supplemented by the proposal for a model to describe the evolution of the Young's modulus and the tensile strength according to the mixture composition., Les matériaux granulaires sont utilisés dans de nombreux domaines tels que la pharmacie, la chimie, la métallurgie, l'agroalimentaire. Ils font l'objet de nombreuses recherches théoriques et expérimentales. La compression en matrice fermée est un procédé économique et facile à automatiser, ce qui explique qu'elle soit très répandue dans les industries qui utilisent des milieux granulaires. Dans le domaine pharmaceutique, le comprimé reste la forme la plus présente sur le marché. Bien que simple en apparence, la compression est un processus dynamique irréversible d'une grande complexité. Dans le cas d'un comprimé pharmaceutique, il faut garder à l'esprit que celui ci doit répondre à la fois à des contraintes technologiques, à des contraintes thérapeutiques et à des contraintes réglementaires très strictes. Pour répondre à ces différentes contraintes, les comprimés pharmaceutiques sont obtenus par la compression de mélanges souvent complexes d'excipients et d'une substance active. Bien que des progrès aient été fait dans la quantification des propriétés mécaniques des systèmes simples, le comportement mécanique des systèmes de poudres plus complexes a été moins étudié. L'idéal pour le formulateur serait de disposer des propriétés de chaque constituant du mélange et de sa contribution au comportement de l'ensemble du système pour pouvoir prédire le comportement des constituants en mélange. L'expérience semble montrer que ce n'est pas aussi simple. Or, comprendre le comportement d'un mélange en fonction des propriétés de ces constituants de base, c'est non seulement pouvoir prédire le comportement du mélange, mais également pouvoir développer de nouvelles formules. L'objectif de ce travail de recherche est d'évaluer les propriétés de mélanges granulaires compactés. Etant donnée la complexité du problème et la difficulté d'interprétation lorsque l'on s'intéresse à des mélanges d'excipients, les études doivent être réalisées sur des systèmes simples (mélanges binaires faisant intervenir des systèmes monodisperses). Il a donc été nécessaire d'étudier de la façon la plus complète possible les systèmes simples choisis avant de pouvoir passer à l'étude de leurs mélanges binaires.Les excipients étudiés (A TAB®, Fast Flo®, Vivapur 12®) sont représentatifs des excipients utilisés dans le domaine pharmaceutique. Les données de la littérature ont également mis en évidence des comportements en compression très différenciés. Le premier objectif de ce travail a donc été de caractériser de la manière la plus exhaustive possible le comportement sous pression des trois excipients ainsi que les propriétés mécaniques de ces systèmes compactés.Les résultats obtenus sur la compressibilité des trois excipients (énergies mises en jeu au cours de la compression, consommation de la porosité, modélisation de Heckel et seuil moyen d'écoulement plastique) ont confirmé des aptitudes à la compression très différentes.En complément, la technique de microtomographie X a été utilisée pour caractériser la fraction solide des comprimés de Vivapur 12®. Cette technique est une technique émergente dans l'étude des comprimés pharmaceutiques. Il a donc été nécessaire au préalable de la valider dans le domaine d'application dans lequel nous voulions la mettre en oeuvre (vérification de la loi de Beer-Lambert). Après une étape de calibration, une hétérogénéité au niveau de la répartition de la masse volumique a été mise en évidence au sein des comprimés, avec une différence importante entre la surface (surdensifiée) et le centre du comprimé. A la vue de ces observations, il apparaît donc que la différence entre les propriétés du volume (résistance à la rupture, module de Young, ...) et les propriétés de surface (dureté en indentation, ...) doit être faite.Concernant les propriétés mécaniques des systèmes simples compactés (résistance à la rupture, module de Young, ténacité, dureté Brinell), des différences ont été observées entre les trois excipients pour une même propriété. De plus, pour un même excipient, des variations marquées entre les propriétés mécaniques caractéristiques du volume du compact et les propriétés mécaniques caractéristiques de la surface ont été mises en évidence.Le modèle de la percolation qui est de plus en plus rencontré dans le domaine de la compression de composés pharmaceutiques a été appliqué aux trois systèmes étudiés. Les résultats de nos essais de modélisation semble montrer que ce modèle présente des limites. L'exposant critique ne semble pas universel pour une propriété donnée et les seuils de densité critique obtenus restent difficile à interpréter.La deuxième partie de ce travail est consacrée à l'étude des mélanges binaires formés à partir des trois excipients étudiés dans la première partie.Le suivi de l'évolution de la porosité des mélanges (à une contrainte de compression donnée) en fonction de la composition massique du mélange a permis de mettre en évidence une relation linéaire Porosité/Composition. Cette relation permet de déterminer la porosité d'un mélange compacté sous une pression donnée à partir des données recueillies au cours de l'étude des systèmes simples. Par contre, le seuil moyen d'écoulement plastique des mélanges n'évolue pas linéairement avec la composition massique du mélange. Mais en raison de la relation précédemment obtenue, une méthode de calcul indirect du seuil moyen d'écoulement plastique est possible. Cette méthode prédictive permet une bonne approximation des propriétés de densification et de déformation d'un mélange binaire quelle que soit sa composition.Pour toutes les propriétés mécaniques étudiées, les lois de proportionnalités simples classiquement utilisées en mécanique ne sont pas applicables. Dans la majorité des cas, une déviation négative est même observée par rapport à ces lois simples.Dans le cas particulier des propriétés mécaniques qui caractérisent la surface des compacts, il est apparu qu'elles étaient régies par le composé le plus plastique du mélange dès que sa proportion massique est égale à environ 30 à 20 %.Pour s'inscrire dans une optique d'aide à la formulation, un modèle a été proposé pour décrire l'évolution du module de Young et de la résistance à la rupture en fonction de la composition du mélange. Après ajustement, une approche basée sur des interactions triangulaires et sur la probabilité de présence de ces interactions semble la plus adaptée.Pour compléter l'étude des systèmes binaires, des essais de microtomographie X ont également été menés sur des mélanges Vivapur 12®/A TAB® compactés. Les représentations obtenues ont permis de mettre en évidence le Vivapur 12® au niveau des surfaces des compacts qui ont été en contact avec les pièces mécaniques. Ces observations confirment les résultats obtenus en microindentation sur ce mélange. Les seuils de percolation des deux excipients ont également été mis en évidence.

For binary mixtures with fixed concentrations of the species, various relationships between the surface tensions and the concentrations are briefly reviewed.

Within a lattice model describing a binary mixture with fixed concentrations of the species we discuss the relation-ship between the surface tension of the mixture and the concentrations.

This paper presents a study of the pore characteristics of the packing of disks by using three computer simulation algorithms: deposition under gravity (DG), random sequential adsorption, and Mason's algorithm. A pore is regarded as corresponding to a triangular subunit obtained from the Voronoi tessellation for monosized packing or radical tessellation for multisized packing, and its size and shape are respectively quantified in terms of equivalent circular diameter and circularity. The results indicate that both pore size and shape distributions are significantly affected by the simulation method, which are considered to be related to the packing constraints imposed in the simulation algorithms. Studies of the DG packing of binary mixtures suggest that the disk size distribution significantly affects packing density, a typical macroscopic property, and microscopic properties such as pore size and shape distributions. Attempts have been made to explain the results in terms of packing mechanisms for packing density and geometrical properties for pore characteristics. Copyright 1997 Academic Press. Copyright 1997Academic Press

Not available, La caractérisation thermodynamique de notre système krypton-méthane sur graphite exfolie a été effectuée par volumétrie d'adsorption entre 72 et 86 k. Cette étude nous a permis de mettre en évidence les phénomènes d'entrainement et de déplacement qui s'effectuent selon une transformation du second ordre. D'autre part, une comparaison de nos résultats expérimentaux avec les prévisions théoriques établies dans le cadre du modèle champ-moyen a montré un bon accord entre les deux. De plus, elle nous a permis de confirmer le caractère quasi-idéal de la solution bidimensionnelle observé expérimentalement. L'étude structurale du même système a été effectuée par diffraction de neutrons. Elle nous a permis de mettre en évidence l'existence d'une limite de solubilité du krypton dans la couche mixte et qui varie en fonction de la température. Enfin, l'étude de la fusion de deux compositions du film mixte nous a permis de confirmer l'existence de la solution bidimensionnelle, ce qui rejoint les conclusions des études théoriques et thermodynamiques

Not available, La caractérisation thermodynamique de notre système krypton-méthane sur graphite exfolie a été effectuée par volumétrie d'adsorption entre 72 et 86 k. Cette étude nous a permis de mettre en évidence les phénomènes d'entrainement et de déplacement qui s'effectuent selon une transformation du second ordre. D'autre part, une comparaison de nos résultats expérimentaux avec les prévisions théoriques établies dans le cadre du modèle champ-moyen a montré un bon accord entre les deux. De plus, elle nous a permis de confirmer le caractère quasi-idéal de la solution bidimensionnelle observé expérimentalement. L'étude structurale du même système a été effectuée par diffraction de neutrons. Elle nous a permis de mettre en évidence l'existence d'une limite de solubilité du krypton dans la couche mixte et qui varie en fonction de la température. Enfin, l'étude de la fusion de deux compositions du film mixte nous a permis de confirmer l'existence de la solution bidimensionnelle, ce qui rejoint les conclusions des études théoriques et thermodynamiques

We consider a porous solid, or a gel, saturated by a two fluid system A + B, in the limit where the thickness ξ of the AB interface is smaller than the pore size D. The solid prefers to be in contact with one of the fluids (A). But, if we decrease the chemical potential of B, the B fluid enters the structure. We discuss the reversible penetration process, and find two distinct modes : a) « Capillary invasion » with clusters of B regions growing progressively. b) « Flip process » where all pores are abruptly invaded by B (except possibly for a thin sheath of thickness ξ near the walls). The « fields » H (= chemical potential changes) required to perform capillary invasion (Hc ) or flip (Hf) are in ratio : Hf/ Hc ≅ (ξ/D)2-df where df is the fractal dimension of the pore surface. Gels made with rod-like molecules have df = 1, while flexible chains in good solvents have df = 5/3. For all gels the flip process should dominate, and we expect a sharp transition. On the other hand, porous solids (d f = 2) require a special discussion. Modeling the pores as interconnected capillaries of random diameter D, we find that capillary invasion dominates in this case, and we expect no sharp transition.