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International audience; Plastic debris in the marine environment are the subject of an extensive literature. According to studies dedicated to the determination of plastic litter abundance and to the characterisation of degradation and fragmentation processes, models were used to estimate the global plastic debris abundance and to simulate their transfer and distribution. Despite these efforts, there is still missing plastic in the models used as areas exist where plastic abundance is less than that estimated. In parallel, microplastics presence in the atmosphere and in remote areas was confirmed suggesting long range atmospheric transport. Potentially addressing both these issues, recent literature suggests that microplastics (MPs) and nanoplastics (NPs) can be transferred from the marine environment to the atmosphere via the bursting of air bubbles at the sea surface. Nevertheless, to date there is no direct evidence of this transfer. In this study, we evaluate plastic particles transfer as a function of MPs/NPs characteristics and water composition by simulating the bubble bursting phenomenon in a laboratory reactor. Size distribution of transferred particles were recorded, and their plastic nature was confirmed using electron microscopy. Results show that under tested conditions, the transfer is possible but limited to particles smaller than 1 μm. The influence of the presence of proxies of components of the sea surface microlayer in the water was evaluated showing a higher particle transfer rate in the presence of a surfactant (sodium dodecyl sulfate) and no significant effect of polysaccharides (xanthan gum and dextran). The surface state of the particles can alter their behaviour in the aqueous phase and thus their transfer to the atmosphere. The effect of bubble size was also evaluated showing a higher transfer rate with the smaller bubble size. In addition, experiments performed with grounded polyethylene (PE) samples showed higher transfer for UV-aged PE than for pristine PE.

International audience; This paper is devoted to the investigation of the photooxidation of poly(N-vinylcarbazole (PVK) and polyethylene (LDPE) by exposure to λ ≥ 300 nm polychromatic light (SEPAP 12.24) or UV light produced by a new setup equipped with LEDs emitting at 365 nm (LED 365), both at a temperature of 60 °C. Photooxidation was studied by infrared and UV-visible spectroscopies and emission spectroscopy in the case of PVK. The mechanisms by which the oxidation products were formed in both polymers were recalled. Depending on the conditions of ageing, i.e., polychromatic light or exposure to LED 365, the same oxidation products were obtained but with different rates and different relative amounts. This result reflected the influence of the wavelengths on the mechanisms. In the case of PVK, the formation of oxidation photoproducts and yellowing were not impacted, but the kinetics of the decrease in excimer fluorescence, which is linked to the crosslinking of the polymer, were dramatically modified. In the case of LDPE, wavelength effects on the photolysis of ketones by Norrish reactions were observed. As a consequence, irradiations with the LED 365 setup could not be claimed to be representative of polychromatic irradiations because the shortest wavelengths ((300 nm < < 350 nm)) were missing and could not reproduce natural outdoor conditions of weathering.

International audience; We report a combined experimental and theoretical lattice dynamics study of the Ruddlesden–Popper layered compound Sr2TiO4. From inelastic neutron scattering experiments, we derive the generalized phonon density of states of Sr2TiO4. We also report its heat capacity, thermal expansion, and thermodynamic Grüneisen parameters using the calculated bulk modulus and find a large value of about 2. Using Raman scattering experiments under pressure, we discuss a potential structural distortion of the tetragonal structure above 11 GPa, which could be due to nonhydrostatic compression. The mode Grüneisen parameters of the four Raman-active modes are determined and shown to be in reasonable agreement with those obtained by density functional perturbation theory (DFPT) calculations. The temperature behavior of the Raman-active modes was studied, allowing us to determine the implicit volume and explicit anharmonic contributions. Above 400 K, the implicit volume contribution dominates the temperature-induced variation of the four Raman-active modes, whereas, below this temperature, the explicit anharmonic contribution is the dominant contributor to the highest energy mode. Our results underline the importance of anharmonicity in vibration-related properties of Sr2TiO4.

The liquid-phase exfoliation of graphite is one of the most promising methods to increase production and commercial availability of graphene. Because ionic liquids can be easily obtained with chosen molecular structures and tuneable physicochemical properties, they can be use as media to optimise the exfoliation of graphite. The under- standing of the interactions involved between graphite and various chemical functions in the solvent ions will be helpful to find liquids capable of dissociating and stabilising im- portant quantities of large graphene layers. After a step of sonication, as a mechanical precursor, samples of suspended exfoliated graphene in different ionic liquids have been characterised experimentally in terms of flake size, number of layers, total concentration and purity of the exfoliated material. Nine different ionic liquids based on imida- zolium, pyrrolidinium and ammonium cations and on bis(trifluoromethylsulfonyl)imide, triflate, dicyanamide, tricyanomethanide, and methyl sulfate anions have been tested. UV-vis, Raman, X-ray photoelectron and electrochemical impedance spectroscopy in addition to high resolution transmission electron and atomic force microscopy have been selected to characterise suspended exfoliated graphene in ionic liquids. The num- ber of layers in the flakes exfoliated, the size and concentration depend of the structure of the ionic liquid selected. In order to obtain large flake sizes, ionic liquids with bis(trifluoromethylsulfonyl)imide anions and a cation with an alkyl chain of medium length should be selected. Smaller cation and anion favours the exfoliation of graphene. The exfoliation caused the formation of C-H bonds and the oxidation of the graphitic surface.

Microporous AlPO4-54·xH2O, which exhibits the largest pores among zeolites and aluminophosphates with a diameter of 12.7 A, was investigated at high pressure by X-ray powder diffraction and Raman spectroscopy in diamond anvil cells. The material was found to begin to amorphize near 2 GPa using either a nonpenetrating pressure transmitting medium (PTM) silicone oil or no PTM. When H2O is used as a PTM, amorphization begins at a lower pressure of 0.9 GPa. In this case, superhydration effects are observed and higher relative unit cell volumes are observed prior to the beginning of pressure-induced amorphization (PIA) as compared to the experiment in silicone oil due to insertion of the H2O molecules in the pores. In all cases, in these experiments at room temperature, amorphization was irreversible. Ex situ experiments were used to investigate the local structure of pressure-amorphized AlPO4-54·xH2O by nuclear magnetic resonance and by X-ray absorption spectroscopy, which show that, upon increasing pressure,...

Direct fluorination of poly(ethylene-alt-tetrafluoro- ethylene) copolymer (ETFE) was carried out on commercially available ETFE films with pure fluorine gas at ambient atmos- phere. Reaction temperature was either 95 � C or 150 � C and ex- posure time was 20 hours. Analysis of the fluorinated samples was performed by attenuated total reflection Fourier transform Infrared, confocal micro-Raman and 1 H and 19 F magic angle spinning nuclear magnetic resonance spectroscopies, scanning electron microscopy, electron diffraction and X-Ray photoelec- tron spectroscopies, contact angle determination, atomic force microscopy and nanoindentation measurements, and com- pared to those of the virgin ETFE copolymer. Integrity of the bulk materials was verified by investigating the thermal behav- ior of the polymers by thermogravimetric analysis and differen- tial scanning calorimetry. Evidence for the formation of a homogeneous layer of polytetrafluoroethylene with a thickness of several microns at the surface of the copolymers with no degradation of the materials was observed. V C 2011 Wiley Peri- odicals, Inc. J Polym Sci Part A: Polym Chem 49: 1517-1527, 2011

International audience; We report a complete study of the lattice dynamics, dielectric, elastic and piezolectric properties of the hexagonal semiconducting chromium disilicide (CrSi2). From a combined experimental and theoretical study, we have revisited the phonon mode assignments at the zone-center, so that the contradictions met in previous experimental studies between 250 and 300 cm-1 are now explained and understood. We found that the temperature dependence of the Raman frequencies is mainly due to an implicit volume contribution and related to the large Gruneisen parameter. This explains why CrSi2 has a moderate thermal conductivity although its Debye temperature is quite large. Optic and static dielectric constants have also been analyzed and discussed. The elastic constants of CrSi2 are large, but this compound is quite brittle. In addition, the relatively low Poisson coefficient associated to the large negative Cauchy pressure of CrSi2 indicate the angular nature of its bonding. The calculation of its piezoelectric coefficient shows a sizable value with a magnitude similar to that reported for α-quartz. This prediction requires, however, experimental confirmations.

We report an experimental and theoretical vibrational study of the high-performance piezoelectric GeO2 material. Polarized and variable-temperature Raman spectroscopic measurements on high-quality, water-free, flux-grown α-quartz GeO2 single crystals combined with state-of-the-art first-principles calculations allow the controversies on the mode symmetry assignment to be solved, the nature of the vibrations to be described in detail, and the origin of the high thermal stability of this material to be explained. The low-degree of dynamic disorder at high-temperature, which makes α-GeO2 one of the most promising piezoelectric materials for extreme temperature applications, is found to originate from the absence of a libration mode of the GeO4 tetrahedra.

Freezing of water in hydrophilic nanopores ($D=1.2\text{ }\text{ }\mathrm{nm}$) is probed at the microscopic scale using x-ray diffraction, Raman spectroscopy, and molecular simulation. A freezing scenario, which has not been observed previously, is reported; while the pore surface induces orientational order of water in contact with it, water does not crystallize at temperatures as low as 173 K. Crystallization at the surface is suppressed as the number of hydrogen bonds formed is insufficient (even when including hydrogen bonds with the surface), while crystallization in the pore center is hindered as the curvature prevents the formation of a network of tetrahedrally coordinated molecules. This sheds light on the concept of an ubiquitous unfreezable water layer by showing that the latter has a rigid (i.e., glassy) liquidlike structure, but can exhibit orientational order.

Structure and dynamic disorder of the title compound are studied by total neutron scattering coupled with reverse Monte Carlo modeling.

alpha-quartz-type Si1−xGexO2 solid solutions (x=0.06, 0.11, and 0.24) and pure SiO2 were investigated by Raman spectroscopy. Coupled and decoupled vibrational modes were identified at room temperature as a function of composition. Tetrahedral tilting librational modes involved in the displacive alpha beta-quartz phase transition are decoupled. The wave number of the coupled A1 mode located at 464 cm−1 for pure alpha-quartz was found to vary quite linearly with germanium content. Raman spectra were recorded up to 1473 K. Substitution of germanium in the quartz lattice clearly improves the thermal stability of the alpha phase. The alpha beta-quartz phase transition temperature increases from 846±1 K for x=0 to about 1300±50 K for x=0.24. At the same time, the dynamic disorder observed in quartz well below the transition is reduced in the solid solutions.