Relation entre la structure et les propriétés mécaniques de films minces hybrides organiques-inorganiques préparés par voie sol-gel

The sol-gel process allows the easy deposition of hybrid organic-inorganic thin films. Mechanical properties of these hybrids do not depend only on the initial composition but also on the strength of the interactions at the interface between both organic and inorganiccomponents. The present work validates nanoindentation measurements to evaluate reproducibly Young modulus and universal hardness on SiO2-PMMA based hybrid thin films by using specific indentation procedures in order to limit the time dependence of the response. We also studied the influence of the morphology of these nanocomposites on the mechanical properties measured by nanoindentation. At first, we modified the strength of the interactions between organic and inorganic components (weak or strong interactions) ; then, we modified the size of the hybrid interface by changing the inorganic component (sol-gel silica or nanoparticles).Le procédé sol-gel permet l'élaboration aisée de films minces hybrides organiquesinorganiques. Les propriétés mécaniques des matériaux hybrides étudiés sont fixées d'une part par la composition du revêtement et d'autre part par la nature de l'interface entre les composantes organique et inorganique.Cette étude a permis de valider la reproductibilité des mesures de module d'élasticité et de dureté effectuées par nanoindentation sur des matériaux hybrides PMMA–SiO2 par un contrôle efficace des phénomènes viscoélastiques induits par la présence du polymère.Nous avons également étudié l'influence de la morphologie du matériau (c'est-à-dire le rôle de l'interface hybride) sur la réponse mécanique obtenue par nanoindentation ; pour cela, nous avons modifié la nature des interactions établies entre les composantes organique et inorganique. Puis, nous avons modifié la taille de l'interface en modifiant la nature de la composante inorganique

Relation entre la structure et les propriétés mécaniques de films minces hybrides organiques-inorganiques préparés par voie sol-gel

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Iron Oxide and Gold Based Magneto-Plasmonic Nanostructures for Medical Applications: A Review

Iron oxide and gold-based magneto-plasmonic nanostructures exhibit remarkable optical and superparamagnetic properties originating from their two different components. As a consequence, they have improved and broadened the application potential of nanomaterials in medicine. They can be used as multifunctional nanoprobes for magneto-plasmonic heating as well as for magnetic and optical imaging. They can also be used for magnetically assisted optical biosensing, to detect extreme traces of targeted bioanalytes. This review introduces the previous work on magneto-plasmonic hetero-nanostructures including: (i) their synthesis from simple “one-step” to complex “multi-step” routes, including seed-mediated and non-seed-mediated methods; and (ii) the characterization of their multifunctional features, with a special emphasis on the relationships between their synthesis conditions, their structures and their properties. It also focuses on the most important progress made with regard to their use in nanomedicine, keeping in mind the same aim, the correlation between their morphology—namely spherical and non-spherical, core-satellite and core-shell, and the desired applications

Methods for preparing polymer-decorated single exchange-biased magnetic nanoparticles for application in flexible polymer-based films

Background: Magnetic nanoparticles (NPs) must not only be well-defined in composition, shape and size to exhibit the desired properties (e.g., exchange-bias for thermal stability of the magnetization) but also judiciously functionalized to ensure their stability in air and their compatibility with a polymer matrix, in order to avoid aggregation which may seriously affect their physical properties. Dipolar interactions between NPs too close to each other favour a collective magnetic glass state with lower magnetization and coercivity because of inhomogeneous and frustrated macrospin cluster freezing. Consequently, tailoring chemically (through surface functionalization) and magnetically stable NPs for technological applications is of primary importance.Results: In this work, well-characterized exchange-biased perfectly epitaxial CoxFe3−xO4@CoO core@shell NPs, which were isotropic in shape and of about 10 nm in diameter, were decorated by two different polymers, poly(methyl methacrylate) (PMMA) or polystyrene (PS), using radical-controlled polymerization under various processing conditions. We compared the influence of the synthesis parameters on the structural and microstructural properties of the resulting hybrid systems, with special emphasis on significantly reducing their mutual magnetic attraction. For this, we followed two routes: the first one consists of the direct grafting of bromopropionyl ester groups at the surface of the NPs, which were previously recovered and redispersed in a suitable solvent. The second route deals with an “all in solution” process, based on the decoration of NPs by oleic acid followed by ligand exchange with the desired bromopropionyl ester groups. We then built various assemblies of NPs directly on a substrate or suspended in PMMA.Conclusion: The alternative two-step strategy leads to better dispersed polymer-decorated magnetic particles, and the resulting nanohybrids can be considered as valuable building blocks for flexible, magnetic polymer-based devices

Star-Shaped Fe3-xO4-Au Core-Shell Nanoparticles: From Synthesis to SERS Application

In this work, the preparation of magneto-plasmonic granular nanostructures and their evaluation as efficient substrates for magnetically assisted surface enhanced Raman spectroscopy (SERS) sensing are discussed. These nanostructures consist of star-shaped gold Au shell grown on iron oxide Fe3-xO4 multicores. They were prepared by seed-mediated growth of anisotropic, in shape gold nanosatellites attached to the surface of polyol-made iron oxide polycrystals. In practice, the 180 nm-sized spherical iron oxide particles were functionalized by (3-aminopropyl) triethoxysilane (APTES) to become positively charged and to interact, in solution, with negatively charged 2 nm-sized Au single crystals, leading to nanohybrids. These hybrids acted subsequently as nucleation platforms for the growth of a branched gold shell, when they were contacted to a fresh HAuCl4 gold salt aqueous solution, in the presence of hydroquinone, a reducing agent, for an optimized nominal weight ratio between both the starting hybrids and the gold salt. As expected, the resulting nanocomposites exhibit a high saturation magnetization at room temperature and a rough enough plasmonic surface, making them easily attracted by a lab. magnet, while exhibiting a great number of SERS hot spots. Preliminary SERS detection assays were successfully performed on diluted aqueous thiram solution (10−8 M), using these engineered substrates, highlighting their capability to be used as chemical trace sensors

Water Vapor Photoelectrolysis in a Solid-State Photoelectrochemical Cell with TiO2 Nanotubes Loaded with CdS and CdSe Nanoparticles

In this study, polyol-made CdS and CdSe crystalline nanoparticles (NPs) are loaded by impregnation on TiO2 nanotube arrays (TNTAs) for solar-simulated light-driven photoelectrochemical (PEC) water vapor splitting. For the first time, we introduce a safe way to utilize toxic, yet efficient photocatalysts by integration in solid-state PEC (SSPEC) cells. The enabling features of SSPEC cells are the surface protonic conduction mechanism on TiO2 and the use of polymeric electrolytes, such as Nafion instead of liquid ones, for operation with gaseous reactants, like water vapor from ambient humidity. Herein, we studied the effects of both the operating conditions in gaseous ambient atmospheres and the surface modifications of TNTAs-based photoanodes with well-crystallized CdS and CdSe NPs. We showed 3.6 and 2.5 times increase in the photocurrent density of defective TNTAs modified with CdS and CdSe, respectively, compared to the pristine TNTAs. Electrochemical impedance spectroscopy and structural characterizations attributed the improved performance to the higher conductivity induced by intrinsic defects as well as to the enhanced electron/hole separation at the TiO2/CdS heterojunction under gaseous operating conditions. The SSPEC cells were evaluated by cycling between high relative humidity (RH) (80%) and low RH levels (40%), providing direct evidence of the effect of RH and, in turn, adsorbed water, on the cell performance. Online mass spectrometry indicated the corresponding difference in the H2 production rate. In addition, a complete restoration of the SSPEC cell performance from low to high RH levels was also achieved. The presented system can be employed in off-grid, water depleted, and air-polluted areas for the production of hydrogen from renewable energy and provides a solution for the safe use of toxic, yet efficient photocatalysts

Tailoring the magnetic properties of cobalt ferrite nanoparticles using the polyol process

International audienceBackground: In extrinsically magnetoelectric materials made of two components, the direct magnetoelectric coupling arises from a mechanical strain transmission at the interface due to the shape change of the magnetostrictive component under an external magnetic field. Here, the size of the interface between the two components plays a crucial role. Therefore, the development of nanomaterials exhibiting large surface-to-volume ratios can help to respond to such a requirement. However, the magnetic nanoparticles (NPs) must be highly magnetostrictive and magnetically blocked at room temperature despite their nanometer-size. We describe here the use of the polyol process to synthesize cobalt ferrite (CoxFe3−xO4) nanoparticles with controlled size and composition and the study of the relationship between size and composition and the magnetic behavior.Methods: We used an improved synthesis of magnetostrictive CoxFe3−xO4 NPs based on the forced hydrolysis of metallic salts in a polyol solvent, varying the fraction x. Stoichiometric NPs (x = 1) are expected to be highly magnetostrictive while the sub-stoichiometric NPs (particularly for x ≈ 0.7) are expected to be less magnetostrictive but to present a higher magnetocrystalline anisotropy constant, as previously observed in bulk cobalt ferrites. To control the size of the NPs, in order to overcome the superparamagnetic limit, as well as their chemical composition, in order to get the desired magnetomechanic properties, we carried out the reactions for two nominal precursor contents (x = 1 and 0.67), using two different solvents, i.e., triethylene glycol (TriEG) and tetraethylene glycol (TetEG), and three different durations of refluxing (3, 6 and 15 h). The structure, microstructure and composition of the resulting NPs were then investigated by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray fluorescence spectroscopy (XRF), respectively. The magnetic properties were also evaluated using standard magnetometry. To measure the magnetostrictive response of the particles, the particles were sintered to dense pellets on which strain gauges were bonded, measuring the size variation radially, as a function of a dc magnetic field.Findings: We found two samples, the first one being stoichiometric and magnetostrictive, and the second one being sub-stoichiometric and presenting a higher magnetization, that are appropriate to be used as ferromagnetic building blocks in nanostructured magnetoelectric materials, particularly materials based on polymers. We show that the polyol solvent and the reaction time are two key parameters to control the size and the magnetic properties of the resulting nanoparticles. We believe that these results provide relevant insights to the design of efficient magnetic and magnetostrictive nanoparticles that can be further functionalized by coupling agents, to be contacted with piezoelectric polymers.e and composition and the magnetic behavior

Fate of ZnS:Mn quantum dots in Seine River water and seawater. Ecotoxicological effects on Chlorella Vulgaris microalgae

The release of engineered materials into the environment can have detrimental effects on living organisms in ground, rivers, and oceans. Despite the increasing use of nanomaterials, little research is conducted on their degradation. Understanding the biology and environmental consequences of manufactured materials is crucial for preserving the environment and developing more respectful chemistry protocols. Physicochemical studies are essential to understand material behavior and their uptake and distribution within microorganisms. II-VI semiconducting nanocrystals, like ZnS nanoparticles, have emerged due to their quantum confinement, allowing for customization of electronic and optical properties. To assess the toxicity of ZnS QDs doped with Mn2+ and perform ecotoxicological tests, a suitable natural environment and an aquatic model are needed. Microalgae, like Chlorella Vulgaris, offer advantages in ecotoxicology, including environmental relevance, sensitivity, experimental feasibility, ethical considerations, and comparative studies. This paper presents the synthesis of ZnS:Mn NPs with varying concentrations of Mn2+. These NPs induce an antioxidant defense system in algal cells, which may be toxic to Chlorella vulgaris via an oxidative stress mechanism. The toxicity of manganese-doped ZnS nanoparticles does exist but is lower than that induced by a Mn2+ ion concentration of 100 mg L-1

In situ monitored stretching induced α to β allotropic transformation of flexible poly(vinylidene fluoride)-CoFe2O4 hybrid films: The role of nanoparticles inclusion

The purpose of this work is to promote and optimize the formation of the β poly(vinylidene fluoride) (PVDF) phase, known to exhibit the maximum piezoelectric and ferroelectric properties, in free PVDF film as well as in hybrid one containing ferrimagnetic cobalt ferrite nanoparticles inclusions (CoFe2O4 NPs). In practice, uniaxial stretching was applied on both α-neat PVDF and α/β PVDF hybrid films, and the α to β transformation was followed by in situ near-field AFM observations and ex situ XRD, FTIR and DSC experiments. A strong influence of the nano-inclusions was observed on the mechanically induced allotropic transformation. They clearly promote the growth of the electroactive β phase in the PVDF matrix and favour the improvement of the whole film crystallinity. The proposed flexible material processing is easy-to-achieve and low cost. It is very promising for architecting original and smart magnetoelectric devices, in which the piezoelectric phases (β-PVDF) could be well interfaced with the magnetostrictive ones (CoFe2O4)