Conformation des polyélectrolyes dans des films nanométriques assemblés couche par couche

The Layer-by-Layer assembly allows the build-up of multimaterial films with various properties showing a stratified structure. This work describes the structural strudies of multilayer films of polyelectrolytes with neutron scattering measurements.Ageing effect on films was determined by neutron reflectometry. We observed a slight shrink of the films after 5 years and a strong expansion after 15 years.We also showed that the proximity of the substrate and the air at the surface have an influence on the structure of the layers at the extremities of the films, leading to an inhomogeneous structure perpendicularly to the surface.Finally, we studied the conformation of polyelectrolyte chains in the multilayer films ; we determined that PSS chains in dipped films have a flattened coil conformation, whereas the polyelectrolyte chains in solution have a spherical conformation.L’assemblage couche-par-couche permet de fabriquer des films multimatériaux aux propriétés variées présentant une structure stratifiée. Ce travail décrit les études structurelles des films multicouches de polyélectrolytes à l’aide de mesures de diffusion de neutrons.L’effet du vieillissement des films a été déterminé par réflectométrie des neutrons. Nous avons observé un léger tassement des films après 5 ans et une forte expansion après 15 ans.Nous avons aussi montré que le substrat et l’air en surface ont une influence sur la structure des couches proches des extrémités des films, conduisant à une structure inhomogène perpendiculairement à la surface.Nous avons finalement étudié la conformation des chaînes de polyélectrolytes dans les films multicouches ; nous avons déterminé que les chaînes de PSS dans des films préparés par trempage ont une conformation en pelotes aplaties, contrairement aux chaînes de polyélectrolytes en solution qui présentent une conformation sphérique

Conformation des polyélectrolyes dans des films nanométriques assemblés couche par couche

L’assemblage couche-par-couche permet de fabriquer des films multimatériaux aux propriétés variées présentant une structure stratifiée. Ce travail décrit les études structurelles des films multicouches de polyélectrolytes à l’aide de mesures de diffusion de neutrons.L’effet du vieillissement des films a été déterminé par réflectométrie des neutrons. Nous avons observé un léger tassement des films après 5 ans et une forte expansion après 15 ans.Nous avons aussi montré que le substrat et l’air en surface ont une influence sur la structure des couches proches des extrémités des films, conduisant à une structure inhomogène perpendiculairement à la surface.Nous avons finalement étudié la conformation des chaînes de polyélectrolytes dans les films multicouches ; nous avons déterminé que les chaînes de PSS dans des films préparés par trempage ont une conformation en pelotes aplaties, contrairement aux chaînes de polyélectrolytes en solution qui présentent une conformation sphérique.The Layer-by-Layer assembly allows the build-up of multimaterial films with various properties showing a stratified structure. This work describes the structural strudies of multilayer films of polyelectrolytes with neutron scattering measurements.Ageing effect on films was determined by neutron reflectometry. We observed a slight shrink of the films after 5 years and a strong expansion after 15 years.We also showed that the proximity of the substrate and the air at the surface have an influence on the structure of the layers at the extremities of the films, leading to an inhomogeneous structure perpendicularly to the surface.Finally, we studied the conformation of polyelectrolyte chains in the multilayer films ; we determined that PSS chains in dipped films have a flattened coil conformation, whereas the polyelectrolyte chains in solution have a spherical conformation

Hydrology A Science of Nature

Looking beyond a purely scientific discussion of hydrology, the authors of this volume emphasize that mankind needs to recognize the urgency of the situation in which our water is threatened. Providing a comprehensive overview of the broad and complex field of hydrology, the book explores the water cycle, its various components, and its interactions with the environment in which it develops and interacts. Through this work, the authors endeavor to contribute to the sustainable development of our society and our environment

Hydrologie

Cet ouvrage traite des méthodes et techniques des sciences de l’ingénieur dont les objectifs sont la maîtrise des eaux et leur gestion, dans un cadre global de préservation des ressources naturelles. Les notions abordées couvrent les nombreux aspects de la gestion des eaux en relation avec la production alimentaire (irrigation et drainage) et la conservation des milieux naturels. Le concept de maîtrise des eaux renvoie en effet à la fonction de protection qu’exercent les ouvrages et aménagements, en particu- lier à l’égard de la ressource que constitue le sol. Les divers domaines de l’agrohydrologie sont associés et intégrés dans une perspective d’ingénierie environnementale qui met en évidence les liens étroits unissant ces ressources naturelles vitales que sont l’eau et le sol. Articulé en deux parties consacrées d’une part à la description des processus fondamentaux et d’autre part à celle des techniques d’aménagement, cet ouvrage original et pédagogique propose une vision complète, équilibrée et détaillée de plusieurs disciplines, en un ensemble cohérent et rigoureux. Il répond ainsi aussi bien aux besoins de formation des étudiants, qu’à celui de référence pour le praticien

L'unicité de lieu, d'action et de temps

Tribune Libre: The uniqueness of place, action and time We recently had the pleasure of re-reading the Tribunes Libres of Ghislain de MARSILY (1994) and Jacques GANOULIS (1996), especially their discussions of a new typology for hydrological models and the analysis of uncertainty. It appears, however, that some confusion and alternative interpretations of hydrological modelling still persist. It is therefore important, notwithstanding our agreement with many of the authors' points, to re-examine some aspects of hydrological modelling in order to clarify certain ambiguities. A distinction made by de MARSILY, between models conditioned by observable phenomena and the physically-based models employed when no phenomena have been observed, invites criticism in terms of the practices to which it leads. GANOULIS' argument, that physically-based models can provide a viable description of processes if differing spatial and temporal empirical coefficients are used, does not stand up to a detailed analysis of the effects of scale. In other words, the issues addressed by these authors arise from the impossibility of using purely physically-based modelling in practical applications due to the difficulty of taking into account and transcribing the characteristics and unique behaviour of each unit of landscape or sub-catchment. To this we can now respond that there are now other lines of thought concerning what are known as physically-based models. Where distributed modelling is concerned, that all places have unique characteristics is a geographical aphorism. The fact remains that the limitations of modelling, expressed by de MARSILY (1994) as the three principles of uniqueness of place, action and time, can be better defined by performing more detailed analysis in the context of uniqueness. Uniqueness limitations partly explain the wide-ranging developments in modelling in respect of both the theory and tools specific to particular applications. One cannot help but notice that expectations of quantitative prediction in hydrology have increased in parallel with the availability and power of computers. This evolution, however, is essentially due to technological advances rather than real scientific progress. Why? Principally, because of the unique characteristics of catchments: in our view, catchments transcend all available theories concerned with hydrological modelling. Moreover, this does not change if better physical hypotheses are proposed, nor if predictions are made for the variables or "non-observable phenomena" discussed by de MARSILY. In this paper, we address these questions and suggest a relevant approach to hydrological modelling for taking into account the unique character of catchments

Electrocatalytic Properties of Metal Phthalocyanine Tetrasulfonate Intercalated in Metal Layered Simple Hydroxides (Metal: Co, Cu, and Zn).

International audienceA series of hybrid metal (Zn, Cu, and Co) layered simple hydroxides (LSH) functionalized by surfactants, namely, dodecylsulfonate (DS0) or dodecylsulfate (DS–) and by tetrasulfonato metal (Cu, Co)-phthalocyanines, was synthesized by anionic exchange reactions and characterized by ancillary techniques. The electrochemical properties of these compounds were investigated by cyclic voltammetry in phosphate buffer solutions over a wide potential range including that suitable for oxygen reduction. The electroactivity of intralayer metal cations (Cu and Co) was evidenced as a function of the phosphate buffer pH. The redox properties of Co- and Cu-PcTS0 grafted in LSH (Zn, Co, and Cu) were also investigated in neutral pH solution, under argon, air, or O2 atmospheres. Interestingly, these hybrid compounds display an electrocatalytic behavior toward the reduction of oxygen. In particular with CoPcTS0-LSH, a sharp electrocatalytic reduction wave is observed at −0.40 V/Ag-AgCl with an intensity that depends on the oxygen concentration. The formation of a CoPc-O2 grafted species in the presence of oxygen was confirmed by electron paramagnetic resonance spectroscopy

Electrocatalytic Properties of Metal Phthalocyanine Tetrasulfonate Intercalated in Metal Layered Simple Hydroxides (Metal: Co, Cu, and Zn)

A series of hybrid metal (Zn, Cu, and Co) layered simple hydroxides (LSH) functionalized by surfactants, namely, dodecylsulfonate (DS₀) or dodecylsulfate (DS^–) and by tetrasulfonato metal (Cu, Co)-phthalocyanines, was synthesized by anionic exchange reactions and characterized by ancillary techniques. The electrochemical properties of these compounds were investigated by cyclic voltammetry in phosphate buffer solutions over a wide potential range including that suitable for oxygen reduction. The electroactivity of intralayer metal cations (Cu and Co) was evidenced as a function of the phosphate buffer pH. The redox properties of Co- and Cu-PcTS₀ grafted in LSH (Zn, Co, and Cu) were also investigated in neutral pH solution, under argon, air, or O₂ atmospheres. Interestingly, these hybrid compounds display an electrocatalytic behavior toward the reduction of oxygen. In particular with CoPcTS₀-LSH, a sharp electrocatalytic reduction wave is observed at −0.40 V/Ag-AgCl with an intensity that depends on the oxygen concentration. The formation of a CoPc-O₂ grafted species in the presence of oxygen was confirmed by electron paramagnetic resonance spectroscopy