Synthesis and Rheological Properties of Magnetic Chitosan Hydrogel

The aim of the present work is first to synthesis a magnetic chitosan hydrogel (chitosan ferrogel) using the blending method and second to study it rheological behavior. Magnetic components ( maghemite particles γ-Fe2O3 ) were synthesized via a simple chemical co-precipitation route also called Massart's procedure. Before being dispersed in chitosan network, γ-Fe2O3 particles were covered with a cationic polyelectrolyte (Polydiallyldimethylammonium chloride; PDADMAC) and the exact quantity required to cover the entire surface of maghemite particles was determined by Electrophoretic mobility. The successful functionalization of maghemite particles was confirmed by zeta potential measurement. The prepared ferrogel was gelified using glyoxal as crosslinking agent. The effect of continuous magnetic field on rheological properties of the elaborated ferrogel was studied, under controlled temperature before and after the gelation process, using a rotating rheometer fitted with a new magneto-rheological cell. Moreover the influence of iron oxide content on the gelation time of magnetic hydrogel was studied by comparing two ferrogels with different maghemite particles content. Flow and viscoelastic measurements showed that applying magnetic field facilitates the formation of a new structure (column-like arrangements), which was confirmed by in situ optical microscopic observation. Kinetic study was investigated by mechanical spectroscopy and demonstrates that the gelation time depends on both iron oxides content and magnetic field

A structural study of a polymer-surfactant system in dilute and entangled regime: Effect of high concentrations of surfactant and polymer molecular weight

International audienceIn the polymer-surfactant system, increasing the concentration of surfactant leads to structural changes in surfactant micelles. This is expected to influence the polymer conformation in the dilute regime where polymer chains are singles and in the entangled regime where the polymer system is described by the blob concept. In this report, the effect of large Sodium bis(2-ethylhexyl) sulfosuccinate (AOT), surfactant concentrations on the conformation of two polyvinylpyrrolidone (PVP) molecular weight (M w ¼ 55000 g/ mol and M w ¼ 360000 g/mol) was discussed. In the first part, in the dilute regime, C PVP 3C*where polymer chains are considered isolated, the determination of PVP (M w ¼ 55000 g/mol and M w ¼ 360000 g/mol) intrinsic viscosity ½h showed a coil to globule transition with the increase of temperature. Electrical conductivity measurements have shown the morphological transition (sphere-cylinder) of surfactant micelles with the increase of surfactant concentrations. The addition of AOT wormlike micelles revealed the expansion of PVP chains for the two molecular weight. In the second part, in PVP entangled regime,C PVP x16C* where overlapped polymer chains form molecular blobs, the addition of AOT wormlike micelles to PVP solutions doesn't affect the Newtonian behavior of PVP (M w ¼ 55000) and the pseudo-plastic behavior of PVP (M w ¼ 360000 g/mol). However, AOT surfactant reinforces significantly the dynamic viscosity of PVP,h for the two molecular weight. By fitting the PVP viscosity-temperature dependence with Fulcher-Tammann-Vogel law, the results showed that the more the surfactant is added, the stronger the PVP solution becomes, which proves that AOT cylindrical (wormlike) micelles presence enhances the solid character of PVP solutions

Mobilization and transformation of mercury across a dammed boreal river are linked to carbon processing and hydrology

Reservoirs are known to accelerate the mobilization and cycling of mercury and carbon as aresult of flooding of terrestrial organic matter, which can lead to environmental concerns at local andbroader spatial scales. We explored the covariation of mercury (Hg) and carbon (C) functional pools innatural and recently dammed portions of the aquatic network of the Romaine River watershed in NorthernQuebec, Canada, to understand how the fate of these elements varies across systems with contrastinghydrology and environmental conditions. We found that total Hg (THg) concentrations in surface waterswere relatively constant along the network, whereas both the concentrations and proportions of MeHgtended to increase in reservoirs compared to surrounding nonooded systems, and along the cascade ofreservoirs. Whereas THg was related to total and terrestrial pools of dissolved organic carbon (DOC), MeHgwas weakly related to DOC but strongly linked to surface concentrations of CO2, as well as toconcentrations of iron and manganese. The latter are proxies of cumulative organic matter processing withinthe network, presumably in anoxic portions of shallow bays, deep reservoir waters, and river sediments,as well as in prior seasons (e.g., under ice). Our results suggest that these deep boreal reservoirs acted more astransformation sites for Hg that was already present than as mobilizers of new Hg, and that under icemetabolism plays a role in MeHg production in these systems as we found strong dichotomies in MeHgpatterns between spring and summer

Auditory event-related potentials

Auditory event related potentials are electric potentials (AERP, AEP) and magnetic fields (AEF) generated by the synchronous activity of large neural populations in the brain, which are time-locked to some actual or expected sound event

Transition phase micellaire-phase eponge induite par laser dans une microemulsion

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Etude cinetique et modelisation des propriétés rhéologiques pendant la transition sol-gel (application aux alcoxydes de silicium)

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Viscoélasticité et structure de gels à base de chitosane (relations avec les propriétés diffusionnelles de macromolécules dans ces biogels)

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Chapitre 6 : Systèmes évolutifs

International audienceExiste-t-il un lien entre les bétons auto-plaçants, les fluides de forages pétroliers,les gels utilisés en agro-alimentaire, en cosmétique ou en médecine ? Bien que cela paraisse contre-intuitif, la réponse est oui : tous ces matériaux ont des propriétés qui évoluent dans le temps et seront qualifiés par la suite de matériaux évolutifs.De nombreux milieux fluides, appelés fluides thixotropes, voient par exemple leur résistance à l’écoulement diminuer au cours du temps lorsqu’on les cisaille après un long temps de repos. On parle de déstructuration ou de rajeunissement. Cette déstructuration est réversible : le matériau laissé au repos va tendre à revenir progressivement vers son état de départ, caractérisé par une résistance à l’écoulement de plus en plus élevée au cours du temps ; on parle alors de structuration ou de vieillissement