Jenny Jouin

Polycrystalline α-alumina / yttrium-aluminum garnet (YAG) fibers were prepared from aqueous solutions of aluminum formoacetate and yttrium acetate, with α-Al ₂ O ₃ nanoparticles as a seeding material. α-Al ₂ O ₃ /YAG fiber production was achieved via dry-spinning, using polyvinylpyrrolidone as a spinning aid, followed by calcination and sintering of as-spun fibers at various temperature, dwell time and heating ramp. X-ray diffraction analysis evidenced the formation of transitional Al ₂ O ₃ and yttrium-aluminum perovskite (YAP) phases (1000-1300 °C) before a full conversion to α-Al ₂ O ₃ / YAG (76 / 24 wt%) at 1500 °C. Full densification required temperatures of at least 1400-1500 °C with a sufficient dwell time (30 min), while increasing sintering temperature induced grain growth. Depending on the thermal treatment, tensile strength and creep factor m of the related fibers could be tailored, either to higher strength at 1400 °C (up to 1149 MPa, m = 0.57) or higher creep at 1500 °C (up to 906 MPa, m = 0.69).

In this study, the local‐scale structure of geopolymers shaped by extrusion or 3D printing was investigated and correlated to the reactivity of the raw materials. The reactivity of the different metakaolin mixtures was evaluated using zeta potential measurements with different alkali silicate solutions, followed by shaping via 3D printing; additionally, the different networks formed were identified via NMR spectroscopy. The results showed that in the presence of weakly reactive basic solutions, the Al(OH)₄⁻ species were released in low amounts due to an increase in the polymerized silicate species in the solution, resulting in a low zeta potential in absolute value. Conversely, for more reactive solutions, the silicate species were more depolymerized, and the siliceous and aluminous metakaolin species were more easily released in solution, resulting in increasingly low zeta potential values. Some samples were 3D printed with metakaolin mixtures using different printers and silicate solutions (K, KNa) with alkaline cation concentrations of [M] > 2.8 M in the mixtures; here, the metakaolin zeta potential values were greater than −50 mV, and the local‐scale structure consisted of more than 50% geopolymer networks (Q⁴(3Al) + Q⁴(2Al)).

To optimize the use of hollow‐core photonic crystal fibers (HC‐PCF), their cores are filled with an atomic gas for an ultra‐enhanced interaction with an incident laser beam in applications such as atomic vapor microcells. One challenge in these gas‐filled HC‐PCFs is to control the physiochemical interactions between the gas medium and the silica inner surface of the fiber core surround. In this work, thus, the processing of ceramic coatings on glass substrates by chemical solution deposition is focused on. Also, the successful implementation of an original coating procedure for a deposition inside hollow‐core fibers with complex microstructures is described. It is indeed possible to form a thin, dense, inorganic, and amorphous layer with a low thickness, low roughness, and high transparency. To obtain such a result, several parameters must be controlled, including the concentration of the solution, the technique and the deposition time, as well as the heat treatment undergone by the fiber. In particular, the selected aluminosilicate coatings, which are nonporous and present a 20–30 nm thickness, demonstrate a considerable improvement of the lifetime properties of the fibers filled with rubidium vapor, without modifying its original guiding properties.

Caffeic acid (CA) exhibits a myriad of biological activities including cardioprotective action, antioxidant, antitumor, anti-inflammatory, and antimicrobial properties. On the other hand, CA presents low water solubility and poor bioavailability, which have limited its use for therapeutic applications. The objective of this study was to develop a nanohybrid of zinc basic salts (ZBS) and chitosan (Ch) containing CA (ZBS-CA/Ch) and evaluate its anti-edematogenic and antioxidant activity in dextran and carrageenan-induced paw edema model. The samples were obtained by coprecipitation method and characterized by X-ray diffraction, Fourier transform infrared (FT-IR), scanning electron microscope (SEM) and UV-visible spectroscopy. The release of caffeate anions from ZBS-CA and ZBS-CA/Ch is pH-dependent and is explained by a pseudo-second order kinetics model, with a linear correlation coefficient of R² ≥ 0.99 at pH 4.8 and 7.4. The in vivo pharmacological assays showed excellent anti-edematogenic and antioxidant action of the ZBS-CA/Ch nanoparticle with slowly releases of caffeate anions in the tissue, leading to a prolongation of CA-induced anti-edematogenic and anti-inflammatory activities, as well as improving its inhibition or sequestration antioxidant action toward reactive species. Overall, this study highlighted the importance of ZBS-CA/Ch as an optimal drug carrier.

Acid‐based geopolymers are known for their high temperature resistance and good mechanical performances. Some compositions also exhibit water resistance, which make them suitable for outdoor applications. This work aims to understand accurately the steps occurring during the geopolymerization process and focuses on the type of networks forming at early stages of the reaction. The sample, prepared from metakaolin and phosphoric acid, has been analyzed at different durations and temperatures during its solidification, in order to identify which compounds would crystallize. The structural characterizations have been performed using Fourier transform infrared spectroscopy and X‐ray diffraction. Several Al–O–P compounds and especially AlPO ₄ polymorphs crystallize in these conditions. They belong to three families of aluminophosphates and are a reliable indication of the amorphous organization of the original sample. The first one is similar to the phases that appear in the phase transition sequences of silica, the second one is composed of AlPO ₄ ‐based zeolites, and the last one is characterized by the presence of aluminum in an octahedral network. The transitions between the different phases are also discussed. Finally, the water resistance of the calcined samples is improved, and the release of acidic species in the water is limited even after a calcination at low temperature.