Anomalous permeation of the [P5W30O110 ]15- polyoxoanion in polyelectrolyte multilayer films

International audienceThe integration of polyoxoanions into functional thin films is of major interest to increase their use as catalysts or to provide new properties to the films. The incorporation of polyoxoanions in polyelectrolyte multilayer (PEM) films has been widely used for such aims. In most investigations, the polyoxoanions were used as a component of the layering process and there is only limited work investigating the interactions of polyoxoanions with preformed PEM films. Herein, we investigated the incorporation of the 30-tungsto-5-phosphate [P 5 W 30 O 110 ] 152 polyoxoanion into PEM films made from hyaluronic acid (HA) and poly(allylamine hydrochloride) (PAH) as a function of the polyoxoanion's concentration. Surprisingly, we found an increased amount of incorporated [P 5 W 30 O 110 ] 152 upon a decrease in its bulk concentration. Confocal Raman microscopy allowed us to investigate the concentration profile of the polyoxoanion across films of about 3 mm in thickness. Homogeneous distribution was only found for films fed with polyoxoanions at the lowest bulk concentration, namely 1.2 6 10 26 M, whereas the films fed with solutions at higher concentrations (1.2 6 10 24 M) showed local enrichment in POM at the film-solution interface. We explain the lower amount of incorporated polyoxoanion at high bulk concentration by the formation of a polyoxoanion-rich barrier reducing further diffusion of the anions in the deeper part of the films

Deposition Mechanism and Properties of Thin Polydopamine Films for High Added Value Applications in Surface Science at the Nanoscale

Polydopamine films have been introduced by Messersmith et al. as a possible “versatile” surface functionalization method allowing to coat the surface of almost all known materials even superhydrophobic surfaces. These new kinds of coatings also confer a plethora of functionalities to the coated materials owing to the complex chemistry of the catechol quinone moieties present on the surface of polydopamine. These coatings may hence become an interesting alternative to established surface coatings like self-assembled monolayers and polyelectrolyte multilayered films. In this review, we describe the knowledge acquired in the last 3 years about the deposition mechanisms of polydopamine films, their properties, and various applications in surface science at the nanoscale.Fonds Europeen de Developpement Economique et Regional (Chaptochem Project 2009-02-039-35

Approche des mécanismes d'oxydation de la pyrite par thiobacillus ferrooxidans grâce à la modélisation morpho-chimique de la surface minérale: Rôle fondamental des phases superficielles oxydées

Non disponible / Not availableA l'échelle de la bactérie, les processus microscopiques qui conduisent à l'oxydation corrosive de la pyrite par Thiobacillus ferrooxidans sont encore mal décrits, tant d'un point de vue microbiologique que d'un point de vue physico-chimique. Pour mieux cerner et comprendre les réactions à l'interface bactérie-minéral, une étude locale à l'échelle micrométrique, de l'interface pyrite-solution, a été réalisée dans ce travail. Les techniques employées (spectroscopies XPS, RAMAN, électrochimie et GC-MS) pour la description physico-chimique de la surface des pyrites oxydées, décapées ou biolixiviées ont permis de caractériser qualitativement ou quantitativement les phases superficielles oxydées (soufre élémentaire, oxyhydroxydes de fer, sulfates ferreux ou ferriques, polysulfures). A cette diversité chimique s'ajoute une hétérogénéité de distribution spatiale des produits d'oxydation, caractérisée et évaluée grâce à la microscopie à force atomique (AFM). Une approche mathématique et statistique de la topographie de la surface minérale a été développée pour établir une modélisation morpho-chimique de l'interface. D'autre part, l'emploi conjoint de techniques microbiologiques, physico-chimiques et spectroscopiques, a établi les liens existant entre les cinétiques de solubilisation, le développement de la corrosion et l'organisation des phases superficielles au cours de la biolixiviation. Résultant exclusivement de l'action du fer(III) à la surface du minéral, ces composés de surface apparaissent comme les seuls substrats solides utilisables par Thiobacillus ferrooxidans, incapable d'oxyder directement la pyrite. Produits indirectement par l'oxydation bactérienne du fer(II) en solution, ils contrôlent aussi la corrosion de la pyrite par leur organisation chimique et leur distribution spatiale. Tous ces résultats fondamentaux permettent de proposer un modèle morpho-chimique dynamique de l'interface pyrite-solution au cours de son oxydation par Thiobacillus ferrooxidans

Deformation of Lactococcus lactis surface in atomic force microscopy study

The surface of the bacterium Lactococcus lactis was investigated under water by contact mode atomic force microscopy (AFM) while varying the imaging parameters (imaging force, scanning velocity, scanning direction). Height images were three-dimensionally (3-D) reconstructed using GOCAD(C) software; this revealed grooves oriented along the scanning direction. Although the grooves were created by the scanning probe, they were not due to a single passage of the probe; the periodicity of the grooves was indeed always three to four times larger than the scanning line periodicity (ratio between the image size and the number of scanning lines). Upon repeated imaging at low force, the grooves were re-created each time with the same morphology; groove depth was increased at higher imaging force. The groove formation is tentatively explained by a deformation of the surface, due to compression or to adhesion, and its slow relaxation. While the grooves reveal a perturbation of the cell surface by the AFM probe, they provide pertinent information about the nanomechanical properties of the cell surface. (C) 2002 Elsevier Science B.V. All rights reserved

Tentative links between thermal diffusivity and fire-retardant properties in poly(methyl methacrylate)–metal oxide nanocomposites

International audiencePossible relationships between fire-retardant properties and thermal diffusivity for poly(methyl methacrylate) (PMMA) filled by melt blending with titanium dioxide (TiO2), alumina (Al2O3) and boehmite (AlOOH) were investigated for a better understanding of the mode of action of metal oxides as fire-retardants (FR) in PMMA. Fire-retardancy was measured with a cone calorimeter and thermal diffusivity (α) by Laser Flash Analysis (LFA). LFA measurements have shown that heat dispersion is higher with titanium dioxide and boehmite than with alumina despite a larger surface area. For thermal diffusivity, discrepancies between the different nanofillers were only visible from 10 wt% onwards. Thermal degradation of PMMA-oxide nanocomposites and their thermal diffusivity could be linked. Moreover, a bi-linear relationship between the peak of heat release rate (pHRR) and the average of heat release rate (AHRR) showed the occurrence of a barrier effect

Influence de l'orientation moléculaire sur l'énergie dissipée lors des tests alternatifs de glissement sur le polyéthylène à ultra haut poids moléculaire

poster presentation + short abstractstatus: publishe

Anomalous permeation of the [P5W30O110 ]15- polyoxoanion in polyelectrolyte multilayer films

International audienceThe integration of polyoxoanions into functional thin films is of major interest to increase their use as catalysts or to provide new properties to the films. The incorporation of polyoxoanions in polyelectrolyte multilayer (PEM) films has been widely used for such aims. In most investigations, the polyoxoanions were used as a component of the layering process and there is only limited work investigating the interactions of polyoxoanions with preformed PEM films. Herein, we investigated the incorporation of the 30-tungsto-5-phosphate [P 5 W 30 O 110 ] 152 polyoxoanion into PEM films made from hyaluronic acid (HA) and poly(allylamine hydrochloride) (PAH) as a function of the polyoxoanion's concentration. Surprisingly, we found an increased amount of incorporated [P 5 W 30 O 110 ] 152 upon a decrease in its bulk concentration. Confocal Raman microscopy allowed us to investigate the concentration profile of the polyoxoanion across films of about 3 mm in thickness. Homogeneous distribution was only found for films fed with polyoxoanions at the lowest bulk concentration, namely 1.2 6 10 26 M, whereas the films fed with solutions at higher concentrations (1.2 6 10 24 M) showed local enrichment in POM at the film-solution interface. We explain the lower amount of incorporated polyoxoanion at high bulk concentration by the formation of a polyoxoanion-rich barrier reducing further diffusion of the anions in the deeper part of the films

Sliding wear behaviour of oriented ultrahigh molecular weight polyethylene

The impact of processing‐induced chain orientation on the sliding wear behaviour of ultrahigh molecular weight polyethylene (UHMWPE) was investigated. The orientation of the molecular network of UHMWPE was done by means of uniaxial tension up to different residual strains. We found that high residual strain levels (higher than 0.45) enabled the sliding dissipated energy of UHMWPE to be decreased in dry conditions. In particular, oriented UHMWPE with a residual strain of 0.85 exhibited, at 500 000 sliding cycles in dry conditions, a decrease in volumetric wear loss by a factor of 3.3 and 19.4 compared with the reference UHMWPE tested in directions parallel and perpendicular to the chain direction, respectively. It is argued that oriented UHMWPE exhibits less adhesion during interfacial wear than the reference material, and hence orientation of UHMWPE bulk may be an alternative treatment to crosslinking for dry sliding conditions. In the case of sliding testing conducted in Ringer's solution, the benefit of the initial chain orientation was quite weak due to a lubrication effect of the solution that markedly limited the effect of chain orientation on the sliding behaviour.status: publishe

Determination of dissipated energy during sliding tests on non-deformed and deformed polyethylene (UHMWPE)

flash presentation + posterstatus: publishe