Porous silica beads produced by nanofluid emulsion freezing

It is shown that porous spherical particles can be obtained via the freezing of silica nanoparticle aqueous suspensions emulsified in a continuous oil phase. After two freeze-thaw cycles, nanoparticles turn aggregated into flocculated objects with microstructure that depends upon emulsion volume fraction and droplet size. For low volume fractions, regular microspheres are produced while for large ones, irregular beads with several tens of micrometer radius are formed. Electronic microscopy, mercury porosimetry and nitrogen adsorption are used to get insights into these porous particles typical radius, pore size distribution, surface area and pore network structure. All exhibit mesopores that result from inter-nanoparticle spacing after flocculation. An unexpected macroporous domain appears which is not observed when drying non-emulsified suspensions. This macroporosity is interpreted as the signature of dendrite formation during the undercooled period, right before freezing occurs. Beside this additional macroporosity, the protocols presented in this article constitute also promising emulsion-based routes for porous material synthesis with original geometry, chemical composition and porosity.Comment: 20 pages, 8 figure

Hot pressing of nanocrystalline TiO2 (anatase) ceramics with controlled microstructure

The preparation conditions of nanocrystalline phase-pure TiO2 anatase ceramics by hot pressing are described. Density, surface area, pore size distribution and grain size are determined by various techniques, including gas adsorption, mercury porosimetry, transmission electron microscopy (TEM) and X-ray diffraction (XRD). The evolution of the structural parameters is followed as function of temperature and pressure programme. It is shown that the porosity, grain and pore size of the ceramics can be controlled by a suitable choice of experimental conditions. Ceramics with densities higher than 90% of the theoretical limit with a mean grain size of 30 nm can be obtained at temperatures as low as 490 ◦C under 0.45 GPa for 2 h. The experimental results are discussed in view of the sintering theory

Microstructure Formation in Freezing Nanosuspension Droplets

The structural evolution of suspensions upon freezing is studied with optical microscopy in a suspended droplet configuration. Droplets have millimeter size and consist in an aqueous mixture of silica particles while the surroundings phase is hexane. Freeze-thaw cycles are applied to this system and a two-step freezing mechanism evidenced. A fast adiabatic growth of dendrites that invade the full droplets is first observed, and occurs within a few milliseconds. Then a slow process lasts for several seconds and corresponds to the release of solidification latent heat into the hexane phase. The striking feature of this work is to evidence that after the first freeze-thaw cycle flocculated microstructures are generated. When a second cycle is performed, microstructures further flocculate and generate, for dense silica suspensions, stable porous spheres of the size of the droplets. A phenomenological description based on repulsion or engulfment of particles by solidifying ice fronts is proposed

Des pratiques et espaces médicaux en transformation : effet générationnel ou conséquence de la féminisation de la profession ?

La féminisation de la profession médicale est un phénomène croissant, de plus en plus étudié par les historiens, sociologues ou médecins qui analysent son impact sur les évolutions du métier dans un contexte d’augmentation des inégalités en matière de santé. Mais alors que les inégalités de répartition des médecins vont croissantes, les géographes se sont peu penchés sur le lien entre féminisation et organisation territoriale de l’offre de soins. De nombreux rapports officiels et travaux scientifiques montrent que les écarts de répartition de médecins augmentent sur le territoire français et à différentes échelles (Maurey, 2013). La tendance actuelle est à la concentration des médecins en zone urbaine et par conséquent un délaissement des zones rurales désignées généralement par l’expression de « déserts médicaux ». L’objectif de cet article est d’explorer les facteurs couramment évoqués et perçus pour expliquer ce phénomène. Parmi ces derniers, nous verrons comment la féminisation de la profession médicale est souvent désignée comme un déterminant central des évolutions actuelles de la médecine et de la distribution inégale des médecins sur le territoire français. Outre la féminisation de la profession de médecins, il convient d’avoir à l’esprit que le secteur médical traverse également de nombreux changements liés au contexte actuel de départ massif à la retraite, à l’application du numerus clausus pendant de longues années et aux attentes de la nouvelle génération de médecins. Face à la diversité des facteurs démographiques, économiques, sociaux et territoriaux qui sont au cœur des changements de la profession, nous déterminerons la manière dont les représentations et les discours associés à la féminisation du métier perdurent et tendent à simplifier les évolutions complexes du métier.The feminization of the physician workforce is a growing phenomenon, increasingly studied by historians, sociologists and physicians who examine the consequences of this shift on the medical profession in a context of increasing health inequalities. While inequality in health worker distribution is also increasing in France, geographers have little studied the relation between feminization and the territorial organization of healthcare provision. Many official reports and scientific studies show that disparities in the distribution of physicians increase over France and at different spatial levels (Maurey, 2013). Considering the workforces of physicians in relation to the French population, the situation of France is quite good but their distribution reveals clear spatial inequalities. Major disparities can be observed between administrative areas, for example “les régions”. As shown in the map below, medical coverage is significantly higher in the French southern regions (particularly Provence-Alpes-Côte-d’Azur with one doctor for 244.77 inhabitants) and also the capital region called Ile-de-France (which one doctor for 252.22 inhabitants). On the contrary, the region called Picardie displays the lowest medical service (one doctor for 388.13 inhabitants) followed by the region Centre (one doctor for 375.43 inhabitants). Inequalities are even stronger within regions at a local level. Medical doctors concentrate mainly in urban areas and therefore neglect rural areas which appear and are described as “medical deserts”. In 2012, 20% of general physicians work in rural areas whereas 27% of French people live there. The objective of this article is to explore the factors commonly discussed and perceived to explain this phenomenon. Among these, the feminization of the medical profession is often designated as a central determinant of the ongoing developments of the medical sector and the increasing spatial disparities among the French territory. We wanted to test the idea that medical deserts exist because of the feminization of the medical profession with local data, collected across the Burgundy region. In Burgundy, the under-representation of female doctors in rural areas is real but the differences observed between the physical locations of male and female doctors are relatively moderate and not significantly different. However, some discourses from the medical sector, political sphere and media tend to associate closely the current increase of the spatial inequalities of medical care and the feminization of medical profession. The tweet from Senator Mayet “medical deserts, the fault of the women?” of 27 July 2015 can certainly appear anecdotal but it still shows an overview of current thinking that can circulate on the effects of the feminization of the medical workforce. To understand the rationales behind medical deserts, it appeared that we should go beyond gendered explanations in order to address the broader social and economic determinants which contribute to this phenomenon. Some recent studies show that young medical practitioners, both women and men, wish to preserve time for family or for social activities leading them to reconsider their relationships to work (Deriaz et al. 2010). In 2003, Robert Herin already stated about the liberal healthcare provision in Normandy that the new generations of physicians (regardless of gender) were seriously concerned by living environment, educating children, the range of jobs for spouses, the qualities of cultural and social environment, etc. All these determinants tend therefore to lead young doctors towards urban environments more than rural areas. As a consequence, we must consider the spatial disparities observed among the medical physicians in France more as a generational issue than a simple gendered issue

Thermodynamics of hydration of MX80-Na: an experimental study of the hydration energies

Hydration properties of swelling clay minerals may be very variable depending on the chemical composition of the clay, on the nature of the interlayer cations and on the interlayer charge (Berend et al., 1995; Vieillard et al., 2011). The Wyoming smectite has been largely studied, notably for assessing its hydration behavior as a function of the interlayer cations, in connection with its structural characteristics (Ferrage et al., 2005; Salles et al., 2007). In the present work, carried out as part of a collaborative Andra/BRGM/HydrASA research program for ThermoChimie project, we propose an original experimental study, based on adsorption and desorption isotherms performed on MX80 clay samples. The goal is to determine energetic contributions to the reactions of hydration, which have been revealed to be non-negligible with respect to the stability of the clay minerals (Gailhanou et al., submitted). In particular, the present work addresses the problems of the hysteresis loop between adsorption and desorption isotherms and of the irreversibility of hydration reactions. This is directly related to the application of classical thermodynamics to the hydration reactions of clay minerals. In a first stage, an experimental study is dedicated to better understand the origin of the hysteresis loop which is systematically observed for the adsorption-desorption isotherms at 25°C. The development of the hysteresis loop has been studied by considering several kinetically related parameters: stabilization periods, temperatures (from 25°C to 60°C) and hydration steps (Figure 1). No sensible change was observed in the hysteresis loop. Therefore, the amount of adsorbed water depends on the followed reaction pathway (adsorption or desorption). The variations in microstructures and in the distribution of hydration layers (0/1/2 water layers; Ferrage et al., 2005) as a function of relative humidity (RH) could provide a possible explanation for this phenomenon

Monte Carlo simulations of krypton adsorption in nanopores: Influence of pore wall heterogeneity on the adsorption mechanism

We present molecular simulation results of the adsorption of krypton in a model of MCM-41 mesoporous material. The adsorption isotherm and adsorption enthalpies have been studied at 77 K. The comparison of experimental and simulation data allows us to analyze how the available interaction models (Kr–Kr and Kr–walls) are able to reproduce the experimental situation. The role of the heterogeneous interactions versus homogenous model is studied and compared with the previous simulation results of nitrogen adsorption in MCM-41. The results show that a model of ideal cylindrical pores gives qualitatively and quantitatively different results. A distribution of the adsorption sites must exist to explain the loading at low pressure (below capillary condensation). Such distribution in MCM-41 is a consequence of non-homogenous walls that contain a wide variety of attractive sites ranging from weakly attractive silica-type to highly attractive regions. In our simulations, the MCM-41 structure is modeled as an amorphous array of oxygen and silicon atoms, each one interacting with an adsorptive atom via the atom-atom potential. The distribution of the adsorption sites is merely a consequence of local atomic structure. Such a model of the wall reproduces the smooth increase in loading seen experimentally

Effect of porogen solvent on the synthesis of nickel ion imprinted polymer materials prepared by inverse suspension polymerization

Ion-imprinted polymers (IIPs) for nickel were synthesized by inverse suspension copoly-merization of vinylbenzyl iminodiacetic acid (VbIDA) with ethyleneglycol dimethacrylate (EDMA) in the presence of nickel(II) ions with various porogen solvents to study their impact on the IIPs properties. They were prepared with mixtures of acetonitrile and dimethylsulfoxide (DMSO), 50/50%v/v, for IIP-A/D and 2-methoxyethanol and DMSO, 50/50%v/v, for IIP-M/D. The structure and properties of these polymers were compared with those of IIP-D previously prepared with pure DMSO as porogen solvent. Although IIP-A/D and IIP-M/D were less porous than IIP-D, they presented better nickel adsorption properties and selectivity towards Zn2+, Co2+ and Pb2+. This is assumed to be the result of the stabilization of the ligand-metal complex during the polymerization process. Moreover, the nickel binding capacities of the prepared IIPs in competitive conditions are remarkably high (184 mu mol/g for IIP-D, 170 mu mol/g for IIP-A/D and 174 mu mol/g for IIP-M/D). The impact of the VbIDA chelating monomer was highlighted by comparing the adsorption properties of a copolymer of methyl methacrylate (MMA) and EDMA with NIP-D. It was proved that the methacrylic polymer matrix has low binding properties. (C) 2016 Elsevier Ltd. All rights reserved.Peer reviewe

Production et caractérisation d'anticorps monoclonaux contre l'histamine

Afin de produire un anticorps monoclonal anti-histamine, des souris sont immunisées par 7 conjugués histamineprotéine en utilisant plusieurs protéines et agents de couplage. Après un premier criblage employant les protéines natives et les conjugués histamine-caséine et histamine-BSA comme antigènes pour identifier les clones qui sécrètent des anticorps monoclonaux, les hybridomes sont clonés par dilution limite et cultivés en ascites. Quatre anticorps monoclonaux ont été seléctionnés (4C9, 4D9, 7E10 .et 9D9 ) et leur spécificité a été étudiée. Les anticorps réagissent avec tous les conjugués histamine-protéine préparés. Mais, ils ne réagissent pas avec les protéines natives, les protéines dérivées ou le conjugué témoin glycine-caséine. De plus, aucune réaction croisée n'a été observée avec les 6 amines biogènes et 2 acides aminés succeptibles d'interférer dans le dosage de l'histamine. L'histamine libre non conjuguée inhibe de façon significative la liaison entre les anticorps etle conjugué histaminecaséine. L'histamine libre inhibe moins efficacement les anticorps que le dérivé histamine-benzoquinone et le conjugué histamine-caséine. L'épitope reconnu par ces anticorps semble être constitué essentiellement par la molécule d'histamine dérivée.Preparation and characterisation of Monoclonal anti-histamine antibodiesIn order to produce monoclonal antibody to histamine, mice are immunized with seven conjugates histamineprotein using several protein and coupling agents. After an initial screening using native protein and histaminecase in, histamine-BSA conjugates as antigens to identify monoclonal antibody secreting clones, the hybridomes are isolated by limiting dilution cloning and grown in ascites. Four antibodies have been selected (4C9, 409, 7E10, 909) and their specificity has been studied. The antibodies react with ail our prepared conjugates histamineprotein. But they are unreactive with native proteins, the derivative proteins, or glycine-casein conjugate. Moreover, no cross-reaction is observed with six biogenic amines and two smino acids that would interfere in the quantitation of histamine. Free unconjugated histamine significantly inhibits antibodies binding to histaminecasein. A much more lower inhibitory potency of free histamine is recorded , as compared to histaminebenzoquinone derivative and to histamine-casein. The main epitope seems encompass the molecule of histamine derived by the coupling agents

Correlation effects during liquid infiltration into hydrophobic nanoporous mediums

Correlation effects arising during liquid infiltration into hydrophobic porous medium are considered. On the basis of these effects a mechanism of energy absorption at filling porous medium by nonwetting liquid is suggested. In accordance with this mechanism, the absorption of mechanical energy is a result expenditure of energy for the formation of menisci in the pores on the shell of the infinite cluster and expenditure of energy for the formation of liquid-porous medium interface in the pores belonging to the infinite cluster of filled pores. It was found that in dependences on the porosity and, consequently, in dependences on the number of filled pores neighbors, the thermal effect of filling can be either positive or negative and the cycle of infiltration-defiltration can be closed with full outflow of liquid. It can occur under certain relation between percolation properties of porous medium and the energy characteristics of the liquid-porous medium interface and the liquid-gas interface. It is shown that a consecutive account of these correlation effects and percolation properties of the pores space during infiltration allow to describe all experimental data under discussion