Surfactant transfer across a water/oil interface: A diffusion/kinetics model for the interfacial tension evolution

International audienceThe transfer of amphiphilic solutes through an interface between water and an organic solvent has been studied numerically by simulations based on a general diffusion/reaction model. This description predicts the evolution of the solute concentrations and the transfer across the liquid/liquid interface. It especially focuses on the dynamic interfacial tension evolution that can be measured by a pendant drop tensiometer. Both the bulk diffusion and the adsorption/desorption rate on both sides of the liquid interface are assumed to contribute to the global transfer kinetic. The calculations provide an understanding on how kinetic exchange at the interface and diffusion transport through the bulk determine the dynamic interfacial tension evolution. In particular, complex interfacial tension evolutions with a non-trivial behavior are predicted in some special cases when diffusion and kinetic exchange are of the same order of magnitude. Finally, this model is used to re-interpret experimental data about Triton X-100 transfer at a water–oil interface

Kinetics of Triton-X100 transfer across the water/dodecane interface: analysis of the interfacial tension variation

International audienceThe interfacial tension of water/dodecane interface is investigated by the pendant drop technique during the transfer of a surfactant molecule, the Triton X-100. This molecule is initially present in one of the liquid phases, and the measurement of the interfacial tension as a function of time permits us to probe the dynamic incoming and outgoing surfactant at the interface and to deduce a rate of transfer. As a rule, after the contact of both solutions, the interfacial tension exhibits a steep initial decrease, passes through a minimum, and then levels off at a value that depends on the initial surfactant concentration in the drop. The time delay before reaching the equilibrium state is due to the limitant step of the surfactant crossing over the liquid/liquid interface. Moreover, the interfacial tension evolution depends strongly on the phase where the Triton-X100 is initially dispersed. Indeed, the global kinetics is found to be faster when Triton X-100 transfers from dodecane toward water as compared to the reverse pathway. To quantify the limiting factors of the interfacial transfer mechanism, two theoretical models describing the time evolution of the system are presented and discussed. The first one is based on a diffusion-controlled adsorption/desorption at the liquid/liquid interface, whereas the second one also takes into account an interfacial chemical adsorption/desorption reaction. This latter permits us to give an estimation of importance of the chemical processes, which occurs at the interface in the overall kinetics

Kinetics of Triton-X100 Transfer Across the Water/Dodecane Interface: Analysis of the Interfacial Tension Variation

The interfacial tension of water/dodecane interface is investigated by the pendant drop technique during the transfer of a surfactant molecule, the Triton X-100. This molecule is initially present in one of the liquid phases, and the measurement of the interfacial tension as a function of time permits us to probe the dynamic incoming and outgoing surfactant at the interface and to deduce a rate of transfer. As a rule, after the contact of both solutions, the interfacial tension exhibits a steep initial decrease, passes through a minimum, and then levels off at a value that depends on the initial surfactant concentration in the drop. The time delay before reaching the equilibrium state is due to the limitant step of the surfactant crossing over the liquid/liquid interface. Moreover, the interfacial tension evolution depends strongly on the phase where the Triton-X100 is initially dispersed. Indeed, the global kinetics is found to be faster when Triton X-100 transfers from dodecane toward water as compared to the reverse pathway. To quantify the limiting factors of the interfacial transfer mechanism, two theoretical models describing the time evolution of the system are presented and discussed. The first one is based on a diffusion-controlled adsorption/desorption at the liquid/liquid interface, whereas the second one also takes into account an interfacial chemical adsorption/desorption reaction. This latter permits us to give an estimation of importance of the chemical processes, which occurs at the interface in the overall kinetics

Premiers résultats concernant le statut du site de Laverune et son organisation spatiale

International audiencePremiers résultats concernant le statut du site de Laverune et son organisation spatial

] Investigation of retention mechanisms of dyes by lamellar materials through vibrational spectroscopy

International audienceSome countries with rich textile industries are nowadays facing water quality issues as a consequence of impacting dye pollution. In addition to their inherent toxicity, dyes induce modification in water acidity or salinity which has harmful consequences on the photosynthesis of aquatic plants. As dye are hardly biodegradable, water treatment is necessary to get ride of them [1], and adsorption treatment appears as a good candidate with efficient low-cost adsorbents, such as clays [2]. As a matter of fact, lamellar materials are widely used for sorbtion of ions and molecules harmful for health and environment. In order to gain in efficiency in the use of such materials, it is essential to get a deeper understanding of the retention mechanisms at the interface solid/liquid. In this work, anionic clays, namely layered double hydroxides (LDH) have been chosen as model compounds in order to study sorption mechanism. The presence of charged layer induce strong anionic exchange capacity in these materials, moreover their composition and structual parameters are easily controled through mastered synthesis process [3]. This study work has been focused on the the mechanisms that can lead to the capture of polluting molecules. Several model dyes have been chosen (MethylOrange - MO, Carmen Indigo - CI et Orange G - OG) for their charge, symmetry and hydrophobicity. Parameters such as the solution concentration and the activity of the solvant, playing with the nature of ions, have also been explored.The work presented here rely on vibrational spectroscopies (Infrared and Raman spectroscopies) sensitive to the intermolecular interaction of the dye with its environment particularly at the interface solid/dye. In parallel, X-Ray Diffraction probes the structural modification in the clay during sorption.The experimental results interpreted though the help of simulations (Monte-Carlo, DFT), lead a fine description of ions sorption at the interfaces with these models lamellar materials

Multiscale Mechanistic Study of the Adsorption of Methyl Orange on the External Surface of Layered Double Hydroxide

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Les meurtriers sexuels

Qu'est-ce qui pousse un individu à commettre un meurtre sexuel ? Quelles étaient les intentions du meurtrier au moment des faits ? Pourquoi une agression sexuelle dévie-t-elle vers l'homicide ? Cette étude, qui repose sur une analyse comparative des violeurs et des meurtriers sexuels, démontre que le meurtre sexuel dépend de la combinaison de facteurs développementaux, intentionnels et situationnels. La colère, la consommation d'alcool, la motivation sexuelle dans l'agression, le sadisme sont autant d'indices qui permettent de comprendre le meurtre sexuel. Cet ouvrage remet en question nombre d'idées reçues sur les meurtriers sexuels. Contrairement à ce que l'on aurait tendance à croire, les sadiques ne représentent qu'une minorité de meurtriers sexuels et les violeurs ont souvent la même histoire criminelle et les mêmes troubles de la personnalité que les meurtriers sexuels. En fait, le parcours criminel des meurtriers sexuels ressemble étrangement à celui des délinquants récidivistes et il apparaît difficile de tracer un profil précis qui les identifierait hors de tout doute possible. Théorique mais aussi pratique, cet ouvrage propose des stratégies d'enquêtes et d'interrogatoires en matière de meurtre sexuel