Vincent Salles

A Review on the Preparation of Borazine-Derived Boron Nitride Nanoparticles and Nanopolyhedrons by Spray-Pyrolysis and Annealing Process

Boron nitride (BN) nanostructures (= nanoBN) are structural analogues of carbon nanostructures but display different materials chemistry and physics, leading to a wide variety of structural, thermal, electronic, and optical applications. Proper synthesis routes and advanced structural design are among the great challenges for preparing nanoBN with such properties. This review provides an insight into the preparation and characterization of zero dimensional (OD) nanoBN including nanoparticles and nanopolyhedrons from borazine, an economically competitive and attractive (from a technical point of view) molecule, beginning with a concise introduction to hexagonal BN, followed by an overview on the past and current state of research on nanoparticles. Thus, a review of the spray-pyrolysis of borazine to form BN nanoparticles is firstly presented. The use of BN nanoparticles as precursors of BN nanopolyhedrons is then detailed. Applications and research perspectives for these OD nanoBN are discussed in the conclusion.

High-yield synthesis of hollow boron nitride nano-polyhedrons

Hollow boron nitride nano-polyhedrons have been successfully prepared by annealing of boron nitride nanoparticles in a nitrogen atmosphere at 1800 °C without a catalyst. In our two-step process, we demonstrated that these boron nitride nanoparticles prepared by spray-pyrolysis of borazine are key precursors to grow these architectures. The samples were carefully analyzed using electron microscopies and Energy-Dispersive X-ray spectroscopy analysis. Based on such characterization tools, the growth mechanism of these architectures has been discussed and detailed. It is noteworthy that these nanostructures are generated via a solid-state transformation in relatively high yields without a metal catalyst and might open new opportunities in exploring chemical and physical properties.

Iron-based 1D nanostructures by electrospinning process

Iron-based 1D nanostructures have been successfully prepared using an electrospinning technique and varying the pyrolysis atmospheres. Hematite (Fe(2)O(3)) nanotubes and polycrystalline Fe(3)C nanofibers were obtained by simple air or mixed gas (H(2), Ar) annealing treatments. Using the air annealing treatment, a high control of the morphology as well as of the wall thickness of the nanotubes was demonstrated with a direct influence of the starting polymer concentration. When mixed gases (H(2) and Ar) were used for the annealing treatments, for the first time polycrystalline Fe(3)C nanofibers composed of carbon graphitic planes were obtained, ensuring Fe(3)C nanoparticle stability and nanofiber cohesion. The morphology and structural properties of all these iron-based 1D nanostructures were fully characterized by SEM, TEM, XRD and Raman spectroscopy.

Surface Entrapment of Fibronectin on Electrospun PLGA Scaffolds for Periodontal Tissue Engineering

Abstract Nowadays, the challenge in the tissue engineering field consists in the development of biomaterials designed to regenerate ad integrum damaged tissues. Despite the current use of bioresorbable polyesters such as poly(l-lactide) (PLA), poly(d,l-lactide-co-glycolide) (PLGA), and poly-ɛ-caprolactone in soft tissue regeneration researches, their hydrophobic properties negatively influence the cell adhesion. Here, to overcome it, we have developed a fibronectin (FN)-functionalized electrospun PLGA scaffold for periodontal ligament regeneration. Functionalization of electrospun PLGA scaffolds was performed by alkaline hydrolysis (0.1 or 0.01 M NaOH). Then, hydrolyzed scaffolds were coated by simple deposition of an FN layer (10 μg/mL). FN coating was evidenced by X-ray photoelectron analysis. A decrease of contact angle and greater cell adhesion to hydrolyzed, FN-coated PLGA scaffolds were noticed. Suitable degradation behavior without pH variations was observed for all samples up to 28 days. All treated materials presented strong shrinkage, fiber orientation loss, and collapsed fibers. However, functionalization process using 0.01 M NaOH concentration resulted in unchanged scaffold porosity, preserved chemical composition, and similar mechanical properties compared with untreated scaffolds. The proposed simplified method to functionalize electrospun PLGA fibers is an efficient route to make polyester scaffolds more biocompatible and shows potential for tissue engineering.

AlN hollow-nanofilaments by electrospinning

We present for the first time an original method to elaborate AlN nanofilaments (NFs) by using a preceramic-based electrospinning process. Initially, an Al-containing precursor (poly(ethylimino)alane) is mixed with an organic spinnable polymer to be electrospun and generate polymeric filaments with a homogeneous diameter. A ceramization step at 1000 °C under ammonia and a crystallization step at 1400 °C under nitrogen are performed to get the final product made of AlN NFs with a diameter ranging from 150 to 200 nm. Studies carried out by high resolution electron microscopy and 3D tomography show their regular morphology, with high chemical purity and polycrystalline nature.

Synthesis of Continuous Conductive PEDOT:PSS Nanofibers by Electrospinning: A Conformal Coating for Optoelectronics

A process to synthesize continuous conducting nanofibers were developed using PEDOT:PSS as a conducting polymer and an electrospinning method. Experimental parameters were carefully explored to achieve reproducible conductive nanofibers synthesis in large quantities. In particular, relative humidity during the electrospinning process was proven to be of critical importance, as well as doping post-treatment involving glycols and alcohols. The synthesized fibers were assembled as a mat on glass substrates, forming a conductive and transparent electrode and their optoelectronic have been fully characterized. This method produces a conformable conductive and transparent coating that is well-adapted to nonplanar surfaces, having very large aspect ratio features. A demonstration of this property was made using surfaces having deep trenches and high steps, where conventional transparent conductive materials fail because of a lack of conformability.

FTIR microscopy contribution for comprehension of degradation mechanisms in PLA-based implantable medical devices

The integration and evolution of implantable medical devices made of bioresorbable polymers and used for temporary biomedical applications are crucial criteria in the success of a therapy and means of follow-up after implantation are needed. The objective of this work is to develop and evaluate a method based on microscopic Fourier Transform InfraRed spectroscopy (FTIR) mappings to monitor the degradation of such polymers on tissue explant sections, after implantation. This technique provided information on their location and on both their composition and crystallinity, which is directly linked to their state of degradation induced predominantly by chain scissions. An in vitro study was first performed on poly(L-lactic acid) (PLLA) meshes to validate the procedure and the assumption that changes observed on FTIR spectra are indeed a consequence of degradation. Then, mappings of in vivo degraded PLLA meshes were realized to follow up their degradation and to better visualize their degradation mechanisms. This work further warrants its translation to medical implants made of copolymers of lactic acid and to other polyesters.Graphical Abstract

Anisotropic ferromagnetic polymer: A first step for their implementation in microfluidic systems

Here we report on the influence of anisotropic microstructure on the performances of magnetically soft micro-patterns intended to integrate microfluidic systems. These micro-patterns are made of a composite obtained by mixing carbonyl iron particles with polydimethylsiloxane, which offers practical integration advantages. We investigated a wide range of magnetic particle loadings, from 10wt% to 83wt%, reaching magnetization as high as 630 kA/m. A homogeneous field was applied during the polymer’s cross-linking phase so that to obtain a 1D arrangement of the particles in the solidified polymer, along the field direction. Here we present the results obtained for square-based micro-pillars prepared under a magnetic field applied along one of its diagonal. We assessed the magnetic anisotropy owing to the particles’ spatial arrangement by comparing the magnetization processes along the two diagonals of the micro-pillar’s base. The magnetic susceptibilities along the two directions differ from a factor greater ...

Physical properties of individual anatase TiO2 nanowires investigated by field emission in a transmission electron microscope

The authors present studies on the field emission (FE) mechanism and the FE-induced transformation of individual anatase TiO2 nanowires (NWs). The NWs were synthesized by electrospinning followed by calcination at 500 °C which produces polycrystalline anatase nanofibers as determined by Raman spectroscopy and transmission electron microscopy (TEM) characterization. Nanowires of ∼100 nm in diameter were individually mounted at the apexes of tungsten tips for further physical characterization. The FE experiments were carried out in a TEM which allows the measurement of the FE current while simultaneously observing structural modifications leading to the NW’s destruction. For low currents (below 100 nA), we observe reproducible FE Fowler-Nordheim I/V characteristics. Higher currents (up to 1 μA) can be obtained but sudden destruction of the NW may take place. Our observations show that a thermally-activated transition occurs and leads to rapid re-crystallization phenomena and a variation of the FE characteri...

Synthesis and Characterization of Advanced Carbon-Based Nanowires – Study of Composites Actuation Capabilities Containing These Nanowires as Fillers

Electromechanical properties in polymers can be employed to create a large number of sen‐ sors and actuators [1-2]. For example they could replace the piezoelectric materials common‐ ly used in Micro Electromechanical Systems (MEMS). Even if the electromechanical coupling is relatively weak for polymers, they can generate high strains due to electrostric‐ tive and Maxwell effects which are a quadratic function of the applied electric field as op‐ posed to a linear function for piezoelectric materials. Other advantages of the polymers are their ease of processability, flexibility and cheapness.