Influence of the Hydrogen Reduction Time and Temperature on the Morphology Evolution and Hematite/Magnetite Conversion of Spindle-Type Hematite Nanoparticles: FH – HES

We report on the transformation via hydrogen reduction of spindle-type hematite nanoparticles into hematite/magnetite hybrid iron oxide particles. The transformation process consists of the reduction of nanoparticles powder in an autoclave using hydrogen gas at a fixed pressure of 11 bars. Both temperature and time of reduction are varied between 300 °C to 360 °C and 0 to 45 h. X-Ray powder diffraction data on the obtained powder and corresponding Rietveld refinement allow the amount of reduced hematite to be determined as a function of these two parameters. Kinetics parameters are measured and an estimation of the activation energy is obtained through linearization of the Arrhenius equation. While reduction is dramatically accelerated at higher temperature, the morphology of the nanoparticles only remain qualitatively unchanged at 300 °C as seen from transmission electron microscopy images. The mechanisms underlying morphology changes are still under study and seem to be closely related to reactor pressure

Hybrid magnetic iron oxide nanoparticles with tunable field-directed self-assembly

We describe the synthesis of hybrid magnetic ellipsoidal nanoparticles that consist of a mixture of two different iron oxide phases, hematite (α-Fe2O3) and maghemite (γ- Fe2O3), and characterize their magnetic field-driven self-assembly. We demonstrate that the relative amount of the two phases can be adjusted in a continuous way by varying the reaction time during the synthesis, leading to strongly varying magnetic properties of the particles. Not only does the saturation magnetization increase dramatically as the composition of the spindles changes from hematite to maghemite, but also the direction of the induced magnetic moment changes from being parallel to the short axis of the spindle to being perpendicular to it. The magnetic dipolar interaction between the particles can be further tuned by adding a screening silica shell. Small-angle X-ray scattering (SAXS) experiments reveal that at high magnetic field, magnetic dipole–dipole interaction forces the silica coated particles to self- assemble into a distorted hexagonal crystal structure at high maghemite content. However, in the case of uncoated maghemite particles, the crystal structure is not very prominent. We interpret this as a consequence of the strong dipolar interaction between uncoated spindles that then become arrested during field-induced self- assembly into a structure riddled with defects

Soft Nanotechnology – from Colloid Physics to Nanostructured Functional Materials

We demonstrate how we can tune the size, shape, surface functionality and properties of nanoparticles and use them as ideal model systems for fundamental investigations as well as for materials applications. In particular we describe ways to create functionalized core-shell particles with various degree of anisotropy and interesting magnetic properties. We show how we can use these particles in order to study the equilibrium and non-equilibrium phase behavior of colloidal suspensions with different interaction potentials and summarize our current understanding of the phenomenon of dynamical arrest, i.e. gel and glass formation. While different nanoparticles are vital for fundamental studies of various aspects of soft condensed matter, they also offer fascinating possibilities in materials science. We will demonstrate this with the example of nanocomposites made through an in situ polymerization reaction

Synthesis and characterization of novel functional electrosterically stabilized colloidal particles prepared by emulsion polymerization using a strongly ionized amphiphilic diblock copolymer

Amphiphilic diblock copolymers such as poly(styrene)-block-poly(styrene sulfonate) (PS-b-PSS) (Matsuoka, H.; Maeda, S.; Kaewsaiha, P.; Matsumoto, K. Langmuir 2004, 20, 7412), belong to a class of new polymeric surfactants that ionize strongly in aqueous media. We investigated their self-assembly behavior in aqueous solutions and used them as an emulsifier to prepare electrosterically stabilized colloidal particles of different diameters between 70 to 400 nm. We determined the size, size polydispersity, effective charge, total dissociable charge, structural ordering, and phase behavior using light scattering, transmission electron microscopy (TEM), small-angle neutron scattering (SANS), and potentiometric titration. These experiments clearly demonstrated that all of the synthesized particles were nearly monodisperse (polydispersity index ≤ 6%). The results of DLS and TEM clearly suggested the existence of hairy particles. The form factors obtained by SANS were well described by a polydisperse sphere model. The estimated total number of dissociable charges per particle was found to be larger than 10⁴e, whereas the effective charges per particle were found to be around 1000e. This significant difference suggested the confinement of charges inside the corona regions of the polyelectrolyte brush shell. Finally, these monodisperse particles were found to self-assemble into 3D ordered colloidal crystalline arrays at a low volume fraction (= 0.00074) that diffract light in the visible region

Preparation and characterization of functional silica hybrid magnetic nanoparticles

We report on the synthesis and characterization of functional silica hybrid magnetic nanoparticles (SHMNPs). The co-condensation of 3-aminopropyltriethoxysilane (APTES) and tetraethyl orthosilicate (TEOS) in presence of superparamagnetic iron oxide nanoparticles (SPIONs) leads to hybrid magnetic silica particles that are surface-functionalized with primary amino groups. In this work, a comprehensive synthetic study is carried out and completed by a detailed characterization of hybrid particles׳ size and morphology, surface properties, and magnetic responses using different techniques. Depending on the mass ratio of SPIONs and the two silanes (TEOS and APTES), we were able to adjust the number of surface amino groups and tune the magnetic properties of the superparamagnetic hybrid particles

Nanoparticle hybrid systems synthesis of a tailored composite model

Des colloïdes de silice sphériques et monodisperses sont préparés par voie sol-gel avec des diamètres compris entre 30 nm et 1 μm. Leur surface est fonctionnalisée par différents silanes permettant des liaisons covalentes ou non avec les chaînes d’un réseau élastomère (PMMA ou PAA), polymérisés in-situ sous lampe UV. Afin de suivre la trajectoire de particules sous cisaillement, il est nécessaire de les rendre fluorescentes. Les marqueurs fluorescents organiques (FITC, RITC) photoblanchissent, notre motivation pour obtenir des particules fluorescentes stables a mené à une nouvelle synthèse pour l’obtention de CdSe quantum dots, à basse température. Cette approche permet la synthèse à grande échelle et à faible coût de particules fluorescente émettant du jaune au rouge. L’incorporation de ces quantum dots évitant tout problème de baisse de l’émission et utilisant un autre agent silane, le 3-propyltrimethoxymercapto silane est également décrite. L’étude in-situ et la caractérisation du nanocomposite obtenu est effectuée utilisant les instruments de tribologie, rhéologie, 3-DLS et SANS. Après preuve faite que toute agglomération et/ou agrégation est évitée dans notre procédé (3-DLS, SANS), des études mécaniques (tribologie, rhéologie) et thermiques (DSC, TGA) ont montrés l’effet du ratio VNP/SS.Ø avec VNP, le volume d’une particule, SS, la surface spécifique d’une particule et Ø, la fraction volumique de particules incorporées, sur le coefficient de friction et la température de transition vitreuse.Spherische und uniform dispergierte SiO2 Silica-Partikel werden durch eine Sol-Gel Synthese mit Durchmesser zwischen 30 nm und 1 μm hergestellt. Die Oberfläche wurde durch verschiedenen Silane funktionalisiert. Die Silane ermöglichen sowohl eine kovalente Bindung an die Polymerketten (PMMA oder PAA), von welches polymerisiert unter einer UV Lampe, als auch eine nicht kovalente Bindung. Um die Partikel unter dem Einfluss von Scherkräften folgen zu können, braucht man fluoreszierende Partikel. Die fluoreszierenden organischen ”dyes” (FITC, RITC) ”photobleachen”, unsere Motivation um stabile fluoreszierende Partikel zu haben, hat zu einer neuen CdSe Quantum Dot Synthese mit niedrigen Temperaturen geführt. Diese erlaubt die Synthese von einer grösseren Menge mit geringen Kosten von fluoreszierenden Partikeln, die zwischen gelb und rot emittieren. Die Einbettung von diesen Quantum Dot ohne Rückgang der Fluoreszenz auf der Oberfläche von den Silica-Partikeln ist auch beschrieben. Dafür braucht man ein anderes Silan: das 3-Propyltrimethoxymercapto Silane. Die in-situ Studie und die Nanokomposite Charakterisierung ist mit Tribologie, Rheologie, 3-DLS und SANS durchgeführt. Nach dem Beweis, dass Agglomerierung und/oder Aggregierung in unserem Prozess vermieden ist, zeigen mechanische (Tribologie, Rheologie) und thermische (DSC, ATG) Untersuchungen den Einfluss von der Ratio VNP/SS.Ø mit VNP , Volumen einem Partikel, SS, die spezifische Oberfläche von einem einzelnen Partikel und Ø, den Volumenanteil von eingebetteten Partikeln auf den Reibungskoeffizient und die Glastemperatur.Spherical and monodisperse SiO2 silica colloidal particles in a range of 30 nm to 1 μm are prepared using sol-gel processes. Their surfaces are functionalized with silane agent allowing covalent bond formation or not with macromolecules chains of a crosslinked elastomer (PMMA or PAA), polymerized under UV light. In order to track particle under shear, there is a need to produce fluorescent particle. As commercial organic dyes (FITC, RITC) show photo bleaching, our motivation to get stable fluorescent particle under UV excitation leads to a new synthesis for CdSe quantum dots at low temperatures. This approach allows the synthesis at large scale and low costs of fluorescent particles emitting from yellow to red. Incorporation of these quantum dots, avoiding any loss in the fluorescence emission and using another silane agent, the 3-propyl trimethoxymercapto silane is also described. An in-situ study and characterization of the nanocomposite is performed using tribology, rheology, 3-DLS and SANS techniques. After proving that agglomeration and/or aggregation are avoided in our process (3-DLS, SANS), mechanical (tribology, rheology) and thermal (DSC, ATG) studies showed the effect of the ratio VNP/SS.Ø with VNP, volume of a single particle, SS, specific surface of a particle and Ø, the volume fraction of incorporated particles, on the friction coefficient, and the glass temperature

Orientational behavior of ellipsoidal silica-coated hematite nanoparticles integrated within an elastomeric matrix and its mechanical reinforcement

The mechanical and orientational properties of IOENs consisting of integrated ellipsoidal SCH spindle-type nanoparticles within an elastomeric matrix are reported. The influence of the SCH surface chemistry, leading either to dispersed nanoparticles or crosslinked nanoparticles within the surrounding elastomeric matrix, is studied by mechanical uniaxial deformation (stress-strain) and SAXS measurements under stress. Without surface modifications, the SCH nanoparticles act as defects, and the Young's modulus of the elastomeric matrix remains unmodified. Surface-modified SCH nanoparticles acting as crosslinkers increase Young's modulus by a factor 1.2. SAXS measurements demonstrate that the integrated ellipsoidal nanoparticles orient upon a deformation larger than 50% independently of the specific integration strategy