Hybrid Nanocomposites with Tunable Alignment of the Magnetic Nanorod Filler

For many important applications, the performance of polymer-anisotropic particle nanocomposite materials strongly depends on the orientation of the nanoparticles. Using the very peculiar magnetic properties of goethite ({\alpha}-FeOOH) nanorods, we produced goethite-poly(hydroxyethyl methacrylate) nanocomposites in which the alignment direction and the level of orientation of the nanorods could easily be tuned by simply adjusting the intensity of a magnetic field applied during polymerization. Because the particle volume fraction was kept low (1-5.5 vol \%), we used the orientational order induced by the field in the isotropic phase rather than the spontaneous orientational order of the nematic phase. At the strongest field values (up to 1.5 T), the particles exhibit almost perfect antinematic alignment, as measured by optical birefringence and small-angle X-ray scattering. The results of these two techniques are in remarkably good agreement, validating the use of birefringence measurements for quantifying the degree of orientational order. We also demonstrate that the ordering induced by the field in the isotropic suspension is preserved in the final material after field removal. This work illustrates the interest, for such problems, of considering the field-induced alignment of anisotropic nanoparticles in the isotropic phase, an approach that is effective at low filler content, that avoids the need of controlling the nematic texture, and that allows tuning of the orientation level of the particles at will simply by adjusting the field intensity

Elaboration de nanoparticules à luminescence persistante dans le rouge-proche infrarouge pour l'imagerie in vivo (synthèse et caractérisations optiques)

Ce travail de thèse concerne l étude de nanoparticules à luminescence persistante dans le rouge-proche infrarouge pour la réalisation de sondes utilisables en imagerie optique in vivo. La luminescence persistante est la propriété que possèdent certains matériaux de continuer à émettre de la lumière après la fin de l excitation durant plusieurs dizaines de minutes. Ces particules présentent l avantage de pouvoir être excitées préalablement à l injection dans le milieu biologique, et éviter ainsi les phénomènes d autofluorescence et d absorption rencontrés en imagerie optique in vivo. Le premier objectif était d optimiser la luminescence persistante de silicates de type CaMgSi2O6 dopés Eu2+, Mn2+, Ln3+ (Ln = Dy, Pr) et la taille des nanoparticules. Nous avons développé une synthèse inspirée du procédé Stöber qui a permis d obtenir des nanoparticules sphériques monodisperses entourées d une couche de silice amorphe. Afin de suivre l influence de la composition chimique sur la luminescence persistante, nous avons fait varier le ratio molaire Ca/Mg/Si, la quantité initiale de TEOS, le ratio et la nature des dopants. Une composition optimale, CaMgSi2O6 : Eu2+ (1%), Mn2+ (5%), Pr3+ (2%), avec une luminescence persistante dans le rouge-proche infragouge beaucoup plus intense et plus longue que les matériaux réalisés jusqu alors constitue le résultat majeur de cette première partie. Le second objectif était de développer de nouveaux matériaux avec des propriétés bimodales, alliant luminescence persistante et propriétés magnétiques. Pour ce faire, nous avons étudié les oxysulfures de gadolinium dopés Eu3+, Ti4+ et Mg2+. Une synthèse par voie hydrothermale a permis d obtenir des nanoparticules hexagonales/sphériques de 50 à 80 nm de diamètre et peu agrégées. En luminescence persistante, seules les bandes d émission caractéristiques de l ion Eu3+ (5Dj 7Fj) sont observées. En Imagerie par Résonance Magnétique, ces composés ont un effet T1 prononcé et un effet T2 observable. Compte tenu des résultats en luminescence persistante et en IRM, Gd2O2S : Eu3+ (5%), Ti4+ (1%), Mg2+ (8%) est un excellent candidat comme agent de contraste bimodal. Le dernier objectif de la thèse était de développer des matériaux à luminescence persistante dans le rouge-proche infrarouge qui soient biocompatibles et biodégradables. Nous avons réalisé des nanoparticules de phosphates de calcium, phase mixte HAp / -TCP, par voie hydrothermale. Pour un dopage Eu2+ (0,5%), Mn2+ (2,5%), Pr3+ (1%), ce matériau présente de bonnes propriétés de luminescence persistante qui ont été testées in vivo en imagerie du petit animal. Nous avons montré qu il est possible de suivre la biodistribution des nanoparticules en temps réel pendant plus de dix minutes sans recourir à une quelconque excitation externeThis work concerns the study of red-near infrared persistent luminescence nanoparticles for the production of probes for in vivo optical imaging. Persistent luminescence is the phenomenon encountered in materials which make them glow in the dark during some time after the end of the excitation. These particles have a major advantage: they can be excited before the injection in the biological medium, so it avoids autofluorescence and absorption phenomena that regularly happen with in vivo optical imaging. The first objective was to optimize the persistent luminescence properties of silicates as CaMgSi2O6 doped Eu2+, Mn2+, Ln3+ (Ln = Dy, Pr) and the size of the nanoparticles. We developed a synthesis based on the Stöber process and spherical nanoparticles coated by amorphous silica were obtained. To follow the influence of chemical composition on persistent luminescence properties, we modified the molar ratio Ca/Mg/Si, TEOS initial concentration, ratio and nature of dopants. One optimal composition, CaMgSi2O6 : Eu2+ (1%), Mn2+ (5%), Pr3+ (2%), with a red-near infrared persistent luminescence more intense and longer than ever before is the main result for this part of study. The second objective was to develop new materials with bimodal properties: persistent luminescence and magnetism. Therefore, we studied gadolinium oxysulfides doped Eu3+, Ti4+, Mg2+.We obtained hexagonal and spherical nanoparticles with a diameter between 50-80 nm. Only the characteristic emission bands of Eu3+ (5Dj 7Fj) were observed on the persistent luminescence spectra. With regard to Magnetic Resonance Imaging experiments, these materials exhibit a strong T1 effect and an observable T2 effect. Looking at the persistent luminescence results and the MRI results, Gd2O2S : Eu3+ (5%), Ti4+ (1%), Mg2+ (8%) is an excellent choice for a bimodal contrast agent. The last goal of this work was to develop red-near infrared persistent luminescence materials which could be biocompatible and biodegradable. We produced calcium phosphate nanoparticles, of mixed phase HAp / -TCP, by hydrothermal synthesis. Doped with Eu2+ (0,5%), Mn2+ (2,5%), Pr3+ (1%), this material exhibit good persistent luminescence properties that were tested in vivo. Using these probes in small animal imaging, we demonstrate that it s possible to follow their in vivo distribution in real time for more than ten minutes without any external illuminationPARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Selective encapsulation and enhancement of the emission properties of a luminescent Cu(I) complex in mesoporous silica

We describe a synthetic approach to prepare new luminescent silica‐based materials through the encapsulation of a neutral copper(I) complex inside the pores of mesoporous silica nanoparticles (MSN). The copper(I) complex is present, in the solid state, as two polymorphs, blue and yellow emissive, and in solution it shows a pale yellow color that is also mirrored by an emission in the yellow‐orange region of the electromagnetic spectrum. The X‐ray structures of single crystals have been obtained for both polymorphs. The complex encapsulation in MSN is achieved by its entrapment inside micelles followed by condensation of the silica source. Interestingly, the entrapment leads to the isolation of only one species. Indeed, the compound inside the MSN exhibits remarkable photophysical properties, showing an intense blue emission in solution and in the solid state. Powder X‐ray diffraction of the hybrid materials proves that the complex entrapped in MSN is indeed the blue polymorph. The confinement provides not only a method to isolate only one form of the complex, but also a certain rigidity, more stability of the system by protection of the complex from undesirable oxidation, leading to a highly emissive material possessing a photoluminescence quantum yield of 65%.peerReviewe