Fluorination of PVC medical devices to prevent plasticizers migration.

Medical devices (MD) are often made of plasticized polyvinylchloride (PVC). However, plasticizers may leach out into infused solutions and expose the patients to a toxic risk. The aim of the present work is to fluorinate plasticized PVC tubular MDs to create a barrier layer on their internal surface, and to study the impact of such a chemical treatment on the migration of the plasticizers. Following fluorination by pure molecular fluorine, the physico-chemical characterization of these modified MDs was carried out using various spectroscopic and microscopic techniques or tensile tests, evidencing the formation of covalent C-F bonds on the surface of the treated samples without modification of their mechanical and optical properties. The migration of plasticizers from fluorinated MDs was assessed using gas chromatography coupled with mass spectrometry and was found considerably decreased in comparison with the pristine MDs. After 24 h, the amount of tri-octyltrimellitate plasticizer (TOTM) detected in migrates from fluorinated MDs was even lower than the limit of quantification. Complementary cytotoxicity assays were performed according to the ISO EN 10993-5 standard, showing that the new fluorinated material does not cause a cytotoxic effect on L929 cells.

Synthesis of NiF2 and NiF2·4H2O Nanoparticles by Microemulsion and Their Self-Assembly.

Superstructures or self-assembled nanoparticles open the development of new materials with improved and/or novel properties. Here, we present nickel fluoride (NiF2) self-assemblies by successive preparatory methods. Originally, the self-assemblies were obtained by exploiting the water-in-oil microemulsion technique as a result of auto-organization of hydrated NiF2 (NiF2·4H2O) nanoparticles. The nanostructuration of NiF2·4H2O nanoparticles was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) data. The size and shape of NiF2·4H2O nanoparticles and their subsequent self-assemblies varied slightly as a function of water-to-surfactant and water-to-oil ratios. Scanning electron microscopy (SEM) and TEM characterizations revealed that the nanoparticles are organized into a succession of self-assemblies: from individual nanoparticles assembled into layers to truncated bipyramids, which further auto-organized themselves into almond-shaped superstructures. Anhydrous NiF2 was achieved by heating NiF2·4H2O self-assemblies under the dynamic flow of molecular fluorine (F2) at a moderate temperature (350 °C). Preservation of self-assemblies during the transformation from NiF2·4H2O to NiF2 is successfully achieved. The obtained materials have a specific surface area (SSA) of about 30 m2/g, more than 60% of that of bulk NiF2. The lithium-ion (Li+) storage capacities and the mechanism of the nanostructured samples were tested and compared with the bulk material by galvanostatic cycling and X-ray absorption spectroscopy (XAS). The nanostructured samples show higher capacities (∼650 mAh/g) than the theoretical (554 mAh/g) first discharge capacity due to the concomitant redox conversion mechanism of NiF2 and solid-electrolyte interphase (SEI) formation. The nanostructuration by self-assembly appears to positively influence the lithium diffusion in comparison to the bulk material. Finally, the magnetic properties of nanostructured NiF2·xH2O (x = 0 or 4) have been measured and appear to be very similar to those of the corresponding bulk materials, without any visible size reduction effect. The hydrated samples NiF2·4H2O show an antiferromagnetic ordering at TN = 3.8 K, whereas the dehydrated ones (NiF2) present a canted antiferromagnetic ordering at TN = 74 K.

A universal fluorous technology toward superhydrophobic coatings.

HYPOTHESIS: Development of a process yielding large-sized non-wettable coatings of immediate applicative interest seems feasible by associating a membrane spining technique with the artificial mimic of a bio-inspired strategy toward water repellency. Accordingly, the question that arises is how to design a multiscale textured and chemically-activated continuous film. EXPERIMENTS: A novel synergic combination of a processing technique and chemical treatment was developed in this purpose. Fluorinated nanocarbons were included in polyvinylpyrrolidone (PVP) microfibers via their addition in a precursor solution for electrospinning. The nanocomposites thus obtained were subsequently treated under gaseous molecular fluorine in mild conditions. FINDINGS: Owing to the reactivity of PVP with F2, both etching and functionalization occurred during such a post-treatment. The chemical modification undergone by PVP upon fluorination has been analyzed and a mechanistic approach proposed. An impressive dual texturing developed at the micro- and nanoscale thanks to the combined action of electrospinning, polymer etching and emergence of the nanofillers. This allowed a stable with time superhydrophobic coating-like film to be achieved.

Exfoliated fluorinated carbons with a low and stable friction coefficient.

Exfoliation appears as a promising way to decrease the friction coefficient of carbon materials. Although there is massive defluorination during exfoliation, the friction coefficient is not increased and an exfoliated structure facilitates the formation of a homogeneous and stable tribofilm. The weakening of the interparticle interactions due to the exfoliation process is the main explanation for the excellent tribological properties. Three representative examples are studied to evidence the efficiency of the thermal shock to prepare solid lubricants or additives for lubricating oils, high temperature graphite fluorides, fluorinated carbon nanofibers and fluorinated nanodiscs. An opened (graphite fluoride) or defect structure (nanofibers) allows the gases formed during the exfoliation to be evolved; the exfoliation is then successful regardless of the C-F bonding. Exfoliation and defluorination occur simultaneously resulting in samples with a low F/C atomic ratio. On the contrary for the case of fluorinated nanodiscs, the exfoliation fails because of cracks and edges as well as the low diameter of the discs.

Large-scale synthesis of fluorinated graphene by rapid thermal exfoliation of highly fluorinated graphite.

Weakly fluorinated graphene nanosheets were efficiently prepared via fast thermal exfoliation of highly fluorinated graphite. This scalable method consists of a fast temperature increase (around 10 °C s-1) of fluorinated HOPG performed under an argon atmosphere, without any post-treatment. The mechanism of exfoliation induced by the defluorination step, evolving volatile fluorocarbons, has been highlighted thanks to thermogravimetric analysis (TGA), high temperature X-ray diffraction (HTK-XRD), X-ray Photoelectron Spectrometry (XPS) studies on temperature, and Raman and infrared spectroscopy. The advantages of the described process are its high-yield for the preparation of fluorinated graphene nanosheets, its ease of implementation and scalability. Moreover, the fluorine content drastically decreases during such a process and graphene layers are slightly functionalized, i.e. conductive contrary to the precursor.

Pulsed Electrochemical Mass Spectrometry for Operando Tracking of Interfacial Processes in Small-Time-Constant Electrochemical Devices such as Supercapacitors.

A more detailed understanding of the electrode/electrolyte interface degradation during the charging cycle in supercapacitors is of great interest for exploring the voltage stability range and therefore the extractable energy. The evaluation of the gas evolution during the charging, discharging, and aging processes is a powerful tool toward determining the stability and energy capacity of supercapacitors. Here, we attempt to fit the gas analysis resolution to the time response of a low-gas-generation power device by adopting a modified pulsed electrochemical mass spectrometry (PEMS) method. The pertinence of the method is shown using a symmetric carbon/carbon supercapacitor operating in different aqueous electrolytes. The differences observed in the gas levels and compositions as a function of the cell voltage correlate to the evolution of the physicochemical characteristics of the carbon electrodes and to the electrochemical performance, giving a complete picture of the processes taking place at the electrode/electrolyte interface.

Solid state NMR study of nanodiamond surface chemistry.

Solid state NMR measurements using 13C, 1H and 19F nuclei (MAS, CP-MAS) underline the surface chemistry of nanodiamonds from different synthesis (detonation, high pressure high temperature and shock compression). The comparison of the spin-lattice relaxation times T1 and physicochemical characterization (spin densities of dangling bonds, specific surface area and Raman and infrared spectroscopies) for the various samples, as synthesized, chemically purified and fluorinated allows the nature and the location of the various groups, mainly C-OH, C-H and C-F to be investigated. C-OH groups are located only on the surface whereas C-H and dangling bonds seem to be distributed in the whole volume. Fluorination was studied as a chemical treatment for purification and change of the hydrophobicity through the conversion of the C-OH groups into covalent C-F bonds.