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

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

Neutral and Charged Polymers at Interfaces

Chain-like macromolecules (polymers) show characteristic adsorption properties due to their flexibility and internal degrees of freedom, when attracted to surfaces and interfaces. In this review we discuss concepts and features that are relevant to the adsorption of neutral and charged polymers at equilibrium, including the type of polymer/surface interaction, the solvent quality, the characteristics of the surface, and the polymer structure. We pay special attention to the case of charged polymers (polyelectrolytes) that have a special importance due to their water solubility. We present a summary of recent progress in this rapidly evolving field. Because many experimental studies are performed with rather stiff biopolymers, we discuss in detail the case of semi-flexible polymers in addition to flexible ones. We first review the behavior of neutral and charged chains in solution. Then, the adsorption of a single polymer chain is considered. Next, the adsorption and depletion processes in the many-chain case are reviewed. Profiles, changes in the surface tension and polymer surface excess are presented. Mean-field and corrections due to fluctuations and lateral correlations are discussed. The force of interaction between two adsorbed layers, which is important in understanding colloidal stability, is characterized. The behavior of grafted polymers is also reviewed, both for neutral and charged polymer brushes.Comment: a review: 130 pages, 30 ps figures; final form, added reference

Separation of Bulk, Surface, and Topological Contributions to the Conductivity of Suspensions of Porous Particles

International audienceElectromigration of ions through porous silica particles dispersed in an electrolyte is studied by conductivity measurements. By determining the suspension conductivity at infinite dilution of particles where the Maxwell equation is applicable, the conductivity of the particles is determined. At high ionic strength, this allows calculation of the tortuosity of the particles. The tortuosity is then used to extract the pore conductivity from the particle conductivity under low ionic strength conditions where the surface conductivity is not negligible. Evolution of pore conductivity, which appears to be related to pore size, is not monotonous when ionic strength increases, showing first a decrease at very low ionic strengths, i.e., in conditions of double layers overlap in the pores, followed by an increase to trend toward the bulk conductivity at high ionic strength. This unexpected behavior can be explained by the fact that the initial surface conductivity in pores is mainly due to the protons, provided by spontaneous dissociation of surface silanol sites in water, which are subsequently exchanged by sodium

Adsorption of Iodine from Aqueous Solutions on to Activated Carbons: Correlation with Nitrogen Adsorption at 77K

The adsorption of iodine has been examined on a set of four microporous charcoals subjected to increasing activation, and also on a Vulcan carbon black used as a non-porous reference. Analysis of the iodine adsorption isotherms and of the corresponding differential enthalpies of displacement is consistent with the nitrogen adsorption data, provided that the slightly larger size of the iodine molecule is kept in mind. The α s method, which is normally applied to adsorption from the gaseous phase, has been usefully extended to these liquid/solid systems and leads to a reasonable micropore volume. This approach provides a useful alternative, especially in those cases where the adsorbent cannot be subjected to drying

Mechanism of ion transport in PEO/LiTFSI complexes: Effect of temperature, molecular weight and end groups

International audienceThe conductivity and viscosity of PEO/LiTFSI complexes are determined as a function of temperature, molecular weight (Mn) and the end group nature in view of the design of future polymer electrolytes. The results show the crucial role of the end groups on the dynamics of polymers at low Mn. A new method is proposed to estimate the glass transition temperature variation as function of Mn and end groups using conductivity data. The conductivity and viscosity plotted at constant friction factor follow a master curve which suggests that the main impact of end groups is to modify the available free volume which governs in turn the segmental dynamics. The anion and cation conductivities are separated using the cationic transport number obtained by pfg-NMR. Finally, an empirical equation based on Rouse dynamics taking into account the effect of the end groups is proposed. It reproduces with a good degree of accuracy the conductivities over the whole temperature and Mn ranges. In agreement with molecular dynamic simulations, at high Mn the limiting step is the jump of the lithium ion from one coordination site to another and is not influenced by the dynamics of the PEO chain reptation, whereas at low Mn the transport is mainly ensured by a vehicular mechanism

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