Florentin Michaux

Ce travail concerne l'étude approfondie des propriétés physicochimiques de plusieurs systèmes à base de tensioactifs non ioniques fluorés et hydrogénés en relation avec la synthèse de matériaux mésoporeux silicatés. L'un des buts recherché est de prévoir les caractéristiques structurales et texturales du matériau en fonction de l'application visée. Nous avons ainsi démontré que la courbe de point de trouble, qui caractérise les systèmes à base de tensioactifs non ioniques, doit être localisée à haute température pour obtenir un matériau structuré. Toutefois, cette condition n'est pas suffisante et le rapport des volumes molaires des parties hydrophiles (VA) et hydrophobes (VB) du tensioactif doit être prise en compte. Ainsi, l'étude de nombreux systèmes mixtes a permis de préciser la gamme des rapports VA/VB compatible avec l’obtention de matériaux organisés. A la suite de ce travail, une étude structurale des micelles a été engagée par des méthodes de diffusion de rayonnements (neutrons, RX). A partir des systèmes fluorés étudiés, nous avons montré que la présence de micelles sphériques favorise la formation de matériaux structurés selon une symétrie hexagonale. De façon complémentaire, le suivi in-situ de la formation de la mésophase hybride a apporté des informations intéressantes sur le mécanisme d'auto-assemblage qui gouverne la génération des silices mésoporeuses structurées. L'effet de l'ensemble des paramètres de synthèse sur les propriétés des matériaux mésoporeux a également été étudié, notamment en faisant appel à la méthode des plans d'expériences. La stabilité hydrothermale marquée des silices mésoporeuses préparées à partir de composés fluorés a été démontrée. Finalement, les propriétés spécifiques des silices mésoporeuses, préparées à partir de micelles fluorées, ont été mises à profit pour la conception de bio-réacteurs. Nous avons ainsi montré qu'une lipase physisorbée à la surface de tels matériaux pouvait catalyser une réaction d'estérification. Ce résultat très prometteur offre des ouvertures pour des applications dans le cadre par exemple du développement d'agro-diesel.

Biochars (BCs) and activated carbons (ACs) are well-known carbon-rich materials that are being increasingly studied in environmental sciences for water treatment applications to remediate pollutant sequestration in soil. This study aimed to assess the impact of Sargasso BC particle size and amendment rate on the environmental availability of DDT and DDT metabolites in two distinct Kazakh soils. These two soils were collected in the vicinity of storehouse facilities in Kyzylkairat and Beskainar that store banned pesticides. They presented very distinct concentration levels of DDT and DDT metabolites. Three different types of carbonaceous matrices were tested: Sargasso BC and two commercial ACs (ORBO^TM and DARCO^©). For the granulometry effect, Sargasso BC was ground, and two particle sizes were tested (150 µm) and compared to an unground material. Four distinct application rates were tested (0.25, 0.5, 1, and 2% (w/w)). After a three-month maturation period, environmental availability was assessed using an ISO/DIS 16751, part B-modified methodology. Interestingly, the best reductions in DDT environmental availability were obtained with the finest particle size (both ACs and Sargasso BC < 150 µm). More specifically, the effectiveness of the strategy seemed to depend on many factors. Firstly, a clear soil effect was demonstrated, suggesting that the more contaminated the soil, the more efficient this strategy may be. Secondly, the results showed that an increase in the amendment rate improves the immobilization of DDT and DDT metabolites. The sequestration material demonstrated different efficiency values (up to 58 ± 4% for Sargasso BC < 150 µm and 85 ± 4% for DARCO at a 2% application rate). Finally, a clear molecule effect was displayed, demonstrating the following immobilization order: p,p’-DDE > p,p’-DDD > p,p’-DDT > o,p’-DDT.

High-quality graphene is an especially promising carbon nanomaterial for developing nanofluids for enhancing heat transfer in fluid circulation systems. We report a complete study on few layer graphene (FLG) based nanofluids, including FLG synthesis, FLG-based nanofluid preparation, and their thermal conductivity. The FLG sample is synthesized by an original mechanical exfoliation method. The morphological and structural characterization are investigated by both scanning and transmission electron microscopy and Raman spectroscopy. The chosen two-step method involves the use of thee nonionic surfactants (Triton X-100, Pluronic^® P123, and Gum Arabic), a commercial mixture of water and propylene glycol and a mass content in FLG from 0.05 to 0.5%. The thermal conductivity measurements of the three FLG-based nanofluid series are carried out in the temperature range 283.15–323.15 K by the transient hot-wire method. From a modeling analysis of the nanofluid thermal conductivity behavior, it is finally shown that synergetic effects of FLG nanosheet size and thermal resistance at the FLG interface both have significant impact on the evidenced thermal conductivity enhancement.

The encapsulation of curcumin in micellar caseins (MCs) and the production of powder were performed by spray-drying. Nearly 97% of the curcumin was retained and the yellow powder showed a typical high casein powder morphology. The hygroscopic properties were determined, slight differences reflected less available hydrophobic sites when curcumin was bound to casein, favoring interactions with water in curcumin-enriched MC powders. No difference was detected on the internal MC structure via SAXS. The antioxidant activity of doped-curcumin powder presented 88% of active curcumin. For 60 days at 40 °C storage, the antioxidant activity of curcumin measured by ABTS and FRAP assays was preserved with a percentage of 82 ± 2.0% and 84 ± 1.1%, respectively. Curcumin doped powders presented similar features to classical casein powders (rehydration and gelling abilities). It was demonstrated that curcumin encapsulation in MCs in its powder form helped in protecting its antioxidant activity without influencing the techno-functional properties of MCs. This study allowed the incorporation of curcumin via the MC matrix as an active food ingredient available in a powder state usable as classical milk powder in several food formulations.