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International audience; Relying on preliminary experiments, in this work we design a tunable 850 nm laser based on a hybrid combination of a liquid crystal micro-cell with nanoimprinted grating and an electrically-pumped GaAs half-VCSEL. The optical design is challenging due to the inherent tolerances of this hybrid technology, the presence of metals in the cavity and the need for single fundamental extraordinary mode emission over the whole tuning range. To ensure proper operation, we introduce for the first time the new concept of anisotropic transverse confinement design. The overall performance is verified by our multiphysics VCSEL suite. Beyond tuning features, we predict side mode suppression ratio and optical power under all working conditions, comparing the performance of liquid crystals with different clearing temperatures. The results qualifies these lasers as viable tunable sources with interesting performance and complementary features compared to other technologies.

Chapter 43; International audience; Gas chemical sensors are strongly affected by drift, i.e., changes in sensors’ response with time, that may turn statistical models commonly used for classification completely useless after a period of time. This paper presents a new classifier that embeds an adaptive stage able to reduce drift effects. The proposed system exploits a state-of-the-art evolutionary strategy to iteratively tweak the coefficients of a linear transformation able to transparently transform raw measures in order to mitigate the negative effects of the drift. The system operates continuously. The optimal correction strategy is learnt without a-priori models or other hypothesis on the behavior of physical-chemical sensors. Experimental results demonstrate the efficacy of the approach on a real problem.

Inspired by biological proteins, artificial water channels (AWCs) can be used to overcome the performances of traditional desalination membranes. Their rational incorporation in composite polyamide provides an example of biomimetic membranes applied under representative reverse osmosis desalination conditions with an intrinsically high water-to-salt permeability ratio. The hybrid polyamide presents larger voids and seamlessly incorporates I–quartet AWCs for highly selective transport of water. These biomimetic membranes can be easily scaled for industrial standards (>m2), provide 99.5% rejection of NaCl or 91.4% rejection of boron, with a water flux of 75 l m−2 h−1 at 65 bar and 35,000 ppm NaCl feed solution, representative of seawater desalination. This flux is more than 75% higher than that observed with current state-of-the-art membranes with equivalent solute rejection, translating into an equivalent reduction of the membrane area for the same water output and a roughly 12% reduction of the required energy for desalination. Inspired by biological models, I–quartet artificial water channels can be incorporated in composite polyamide membranes synthesized via interfacial polymerization, providing biomimetic membranes for desalination.

The metamaterial paradigm has allowed an unprecedented space-time control of various physical fields, including elastic and acoustic waves. Despite the wide variety of metamaterial configurations proposed so far, most of the existing solutions display a frequency response that cannot be tuned, once the structures are fabricated. Few exceptions include systems controlled by electric or magnetic fields, temperature, radio waves and mechanical stimuli, which may often be unpractical for real-world implementations. To overcome this limitation, we introduce here a polymeric 3D-printed elastic metamaterial whose transmission spectrum can be deterministically tuned by a light field. We demonstrate the reversible doubling of the width of an existing frequency band gap upon selective laser illumination. This feature is exploited to provide an elastic-switch functionality with a one-minute lag time, over one hundred cycles. In perspective, light-responsive components can bring substantial improvements to active devices for elastic wave control, such as beam-splitters, switches and filters., Here, the authors present a light-responsive elastic metamaterial whose transmission spectrum can be tuned by light stimuli. More specifically, we demonstrate that an appropriate laser illumination is effective in reversibly widening an existing frequency band gap, doubling its initial value.

A generalized model for breakage and coalescence kernels valid for the entire spectrum of turbulence is proposed and validated. Most of the available kernels in the literature indeed assume that in a turbulent liquid-liquid dispersion, the dispersed droplets have dimension in the inertial subrange, and are affected by eddies with size in the same subrange. These kernels are based on the Kolmogorov second-order structure function, which is valid only in the inertial subrange. However, in most industrially encountered situations, many droplets may have a size in the dissipation range, where the Kolmogorov second-order structure function does not apply. Therefore, a more general description of the energy transferred between these droplets and the turbulent eddies is needed to properly model breakage and coalescence events. In this work, the Coulaloglou and Tavlarides (1977) breakage and coalescence kernels have been modified through the implementation of the second-order structure function proposed by Davidson (2004), along with the Pope (2000) energy spectrum. Turbulent liquid-liquid dispersion experiments at high continuous phase viscosity are performed to test and validate the model. The generalized model is able to predict the experimental Sauter mean diameters at different viscosities, turbulent conditions and dispersed-phase volume fraction without any adjustment of the kernel parameters.

International audience; Two natural zeolite-bearing rocks (one containing clinoptilolite and the other chabazite, phillipsite, and analcime) were Fe-exchanged and thermally treated in a reducing atmosphere at 750 °C for 2 h. Two nanocomposites, formed by the dispersion of Fe nanoparticles in a ceramic matrix, were obtained. The prepared lunar dust simulants also contain Na+, K+, Ca2+, and Mg2+ and other mineral phases originally present in the starting materials. The samples were fully characterized by different techniques such as atomic absorption spectrometry, X-ray powder diffraction, followed by Rietveld analysis, transmission electron microscopy, N2 adsorption/desorption analysis at 77 K, measurements of grain size distribution, magnetic property measurements, broad-band dielectric spectroscopy, and DC conductivity measurements. The results of this characterization showed that the obtained metal–ceramic nanocomposites exhibit a chemical and mineralogical composition and electrical and magnetic properties similar to real moon dust and, thus, appear valid moon dust simulants.

Static (DC) and dynamic (AC, at 14 MHz and 8 GHz) magnetic susceptibilities of single crystals of a ferromagnetic superconductor, EuFe2(As1−xPx)2 (x = 0.23), were measured in pristine state and after different doses of 2.5 MeV electron or 3.5 MeV proton irradiation. The superconducting transition temperature, Tc(H), shows an extraordinarily large decrease. It starts at Tc(H=0)≈24K in the pristine sample for both AC and DC measurements, but moves to almost half of that value after moderate irradiation dose. Remarkably, after the irradiation not only Tc moves significantly below the FM transition, its values differ drastically for measurements at different frequencies, ≈16 K in AC measurements and ≈12 K in a DC regime. We attribute such a large difference in Tc to the appearance of the spontaneous internal magnetic field below the FM transition, so that the superconductivity develops directly into the mixed spontaneous vortex-antivortex state where the onset of diamagnetism is known to be frequency-dependent. We also examined the response to the applied DC magnetic fields and studied the annealing of irradiated samples, which almost completely restores the superconducting transition. Overall, our results suggest that in EuFe2(As1−xPx)2 superconductivity is affected by local-moment ferromagnetism mostly via the spontaneous internal magnetic fields induced by the FM subsystem. Another mechanism is revealed upon irradiation where magnetic defects created in ordered Eu2+ lattice act as efficient pairbreakers leading to a significant Tc reduction upon irradiation compared to other 122 compounds. On the other hand, the exchange interactions seem to be weakly screened by the superconducting phase leading to a modest increase of Tm (less than 1 K) after the irradiation drives Tc to below Tm. Our results suggest that FM and SC phases coexist microscopically in the same volume.

The NEREID project (“NanoElectronics Roadmap for Europe: Identification and Dissemination”) is dedicated to mapping the future of European Nanoelectronics. NEREID’s objective is to develop a medium and long term roadmap for the European nanoelectronics industry, starting from the needs of applications to address societal challenges and leveraging the strengths of the European eco-system. The roadmap will also identify promising novel nanoelectronic technologies, based on the advanced concepts developed by Research Centres and Universities, as well as identification of potential bottlenecks along the innovation (value) chain. Industry applications include Energy, Automotive, Medical/Life Science, Security, loT, Mobile Convergence and Digital Manufacturing. The NEREID roadmap covers Advanced Logic and Connectivity, Functional Diversification (Smart Sensors, Smart Energy and Energy for Autonomous Systems), Beyond-CMOS, Heterogeneous Integration and System Design as well as Equipment, Materials and Manufacturing Science. This article gives an overview of the roadmap’s structure and content., Thanks are extended to the support of the EU, which has been funded the NEREID project as a Cooperation and Support action for three years from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 685559.

International audience

Perfluoropolyalkylethers (PFPAEs) are a class of fluorinated polymers having −OCF2–, −OCF2CF2–, and −OCF2CF(CF3)– as common chain units. The ether linkages distinguish them from other famous fluori...

Laser ablation is an effective method to clean Cu-based alloys. A novel procedure of characterisation was developed involving O isotopes evaluated by ToF-SIMS spectroscopy to assess the driving mechanisms of laser-surface interactions. The presence of re-oxidised compounds was detected, discerning between the oxygen from the corrosion layer and the one introduced by the interaction with the laser (that was generated in a controlled atmosphere of O diluted in N). A set of samples treated with different laser conditions were characterised by FESEM and μRaman. The results have shown that re-oxidation phenomenon can occur and its selectivity depends on the laser conditions., Dr. R. Lahoz wishes to acknowledge professional support of the CSIC Interdisciplinary Thematic Platform “Open Heritage: Research and Society (PTI-PAIS)”. Dr. E. Di Francia would like to acknowledge the European Federation of Corrosion (EFC) – EUROCORR Young Scientist Grant Selection Committee 2016 that stimulated the initial collaboration that subsequently produced this research. Dr. V. Rico thanks the FEDER program through AEI-MICINN (PID2019-110430GB-C21) and Junta de Andalucía (PAIDI-2020 through project P18-RT-3480) for financial support.

International audience; The quest for novel designs for lightweight phononic crystals and elastic metamaterials with wide low-frequency band gaps has proven to be a significant challenge in recent years. In this context, lattice-type materials represent a promising solution, providing both lightweight properties and significant possibilities of tailoring mechanical and dynamic properties. Additionally, lattice structures also enable the generation of hierarchical architectures, in which basic constitutive elements with different characteristic length scales can be combined. In this work, we propose 1D- and 2D-periodic phononic crystals made of spatial frames inspired by a spider web-based architecture. Specifically, hierarchical plane structures based on a combination of frames with a variable cross-section are proposed and exploited to open and enhance band gaps with respect to their non-hierarchical counterparts. Our results show that hierarchy is effective in broadening existing band gaps as well as opening new full band gaps in non-hierarchical periodic structures.

International audience; Large scale elastic metamaterials have recently attracted increasing interest in the scientific community for their potential as passive isolation structures for seismic waves. In particular, so-called “seismic shields” have been proposed for the protection of large areas where other isolation strategies (e.g. dampers) are not workable solutions. In this work, we investigate the feasibility of an innovative design based on hierarchical design of the unit cell, i.e. a structure with a self-similar geometry repeated at different scales. Results show how the introduction of hierarchy allows the conception of unit cells exhibiting reduced size with respect to the wavelength while maintaining the same or improved isolation efficiency at frequencies of interest for earthquake engineering. This allows to move closer to the practical realization of such seismic shields, where low-frequency operation and acceptable size are both essential characteristics for feasibility.

International audience; The ability to program the behavior of magneto-reactive polymers requires the fine control of their magnetic microstructure during each step of the printing process. Here, a systematic study of magnetically driven self-assembly of Fe3O4 nanoparticles into chain-like structures is presented and used in a 3D printable formulation. The kinetics of chains formation, as well as their rotation, are studied by varying several experimental parameters: i.e. the viscosity of the formulation, the content of nanoparticles, the intensity of the applied magnetic field, and its application time. Experimental results are coupled to numerical simulations based on the dipolar approximation model, and the collected data are used to produce a dataset to precisely program the microstructure during the printing step. Thus, a desired microstructure in a 3D printed piece can be obtained by controlling the orientation and the length of the magnetic chains in each printed layer. This is achieved by modifying a commercial Digital Light Processing (DLP) 3D printer to apply magnetic fields of tunable intensity and direction. Finally, as a proof of concept, a pyramid-like structure was 3D printed, where each layer contains a specific and spatially oriented microstructure.

International audience; Additive Manufacturing offers an innovative route for producing high-quality parts in various fields. A bi-material system, consisting in a NiCrAlY bond coat deposited onto a Ni-based Alloy 625 substrate, was manufactured by laser powder bed fusion (LPBF). Test samples were prepared and included SolGel ceramic ZrO2(Y2O3) top coats as well as a specific grain boundary serration (GBS) heat treatment for promoting high temperature resistance. These specimens were subjected to very severe thermal shock cycles between 950 °C and 300 °C, characterized by steep heating and air quenching rates in a state-of-the-art burner rig designed to render gas turbine conditions, and their integrity was compared. While LPBFed NiCrAlY coatings were relatively spared from degradations due to thermal shocks, ceramic top coats exhibited clear spallation. Poor bonding was particularly experienced by specimens subjected to the GBS heat treatment due to the unavoidable formation therein of surface oxides. Numerous cracks were detected within NiCrAlY bond coats, both in tested specimens as well as in pre-cycled as-built ones, which suggested a dominant role of the LPBF process known for generating residual stress. Heat treated specimens exhibited nearly no cracking. Hardness was found to significantly increase within as-built NiCrAlY bond coats as a result of heat exposure during thermal shock cycling and was attributed to precipitations. The fully recrystallized microstructure of heat treated specimens, on the other hand, was found more stable. The present study completes a series of investigations demonstrating the great potential for manufacturing excellent high temperature structural components by means of LPBF as opposed to more constraining conventional routes.

International audience; An important issue in the field of elastic metamaterials is that their dynamic properties, such as the band gap frequencies, are typically fixed once the structure has been designed and fabricated. To overcome this limitation, many efforts have been made to conceive materials with adaptive elastic properties based on piezoelectric materials, temperature and magneto-based techniques, actuated polymers via electromagnetic waves, as well as the application of an external mechanical load. In the present research we present an alternative approach based on light-responsive polymers. We show the possibility to reversibly change the material parameters in specific regions of the unit cells of these structures through external light stimuli, leading to the tunability of their transmission spectrum.

Understanding the transport of sodium ions in ionic liquids is key to designing novel electrolyte materials for sodium-ion batteries. In this work, we combine molecular dynamics simulation and experiments to study how molecular interactions and local ordering affect relevant physico-chemical properties. Ionic transport and local solvation environments are investigated in electrolytes composed of sodium bis(fluorosulfonyl)imide, (Na[FSI]), in N,N-methylpropylpyrrolidinium bis(fluorosulfonyl)imide, [C3C1pyr][FSI], at different salt concentrations. The electrolyte systems are modelled by means of molecular dynamic simulations using a polarizable force field. We show that including polarization effects explicitly in the molecular simulations is required in order to attain a reliable description of the transport properties of sodium in the [C3C1pyr][FSI] electrolyte. The validation of the computational results upon comparison with experimental data allows us to assess the suitability of polarizable force fields in describing and interpreting the structure and dynamics of the sodium salt-ionic liquid system, which is essential to enable the application of IL-based electrolytes in novel energy-storage technologies.

International audience; Applied electrochemistry plays a key role in many technologies, such as Li-ion batteries, fuelcells, supercapacitors, solar cells, etc. It is therefore at the core of many research programs allover the world. However, fundamental electrochemical investigations remain scarce. In par-ticular, electrochemistry is among the fields for which the gap between theory and experimentis the largest. From the computational point of view, there is no classical molecular dynamics(MD) software devoted to the simulation of electrochemical systems while other fields such asbiochemistry or material science have dedicated tools.MetalWalls, a MD code dedicated toelectrochemistry, fills this gap. Its main originality is the inclusion of a series of methods whichallow a constant electrical potential to be applied to the electrode materials. It also allowsthe simulation of bulk liquids or solids using the polarizable ion model and the aspherical ionmodel.MetalWallsis designed to be used on high-performance computers and it has alreadybeen employed in a number of scientific publications. It was for example used to study thecharging mechanism of supercapacitors (Merlet et al.,2012), nanoelectrowetting (Choudhuriet al.,2016) and water desalination devices (Simoncelli et al.,2018).

International audience; The use of low frequency waves is the most practical means to investigate nonlinear elastic properties of hysteretic media, such as the strain dependence of wave velocity. Indeed, the rapid increase in damping as a function of frequency makes high frequency waves unable to provide sufficient strain energy to successfully excite nonlinearity. The drawback is that low frequency waves are not suitable for imaging, due to their long wavelength and resulting intrinsic averaging of nonlinear effects over large spatial scales. To address this, we propose here an amplitude modulation of swept sources that allows us to correlate the frequency at which harmonics are detected with the position of the source of nonlinearity, taking advantage of the different strain distributions in the sample at different frequencies.

International audience; The very first step of almost any separation process design procedure is the thermodynamic feasibility analysis. In the case of distillation, residue curve maps (RCMs) represent an essential tool to assess whether the separation is feasible or not. However, the analysis is generally carried out by referring to nominal operating conditions and product purities as specification. This means that, when process parameters are likely to undergo fluctuations, the prediction of the system response is not that obvious. An ABE/W (acetone−butanol−ethanol/water) mixture was then selected as a case study since it allows us to discuss several non-ideal thermodynamic behaviors and because of the renewed interest in biorefinery and sustainable processes during recent years. Residue curve mapping was then exploited to determine the thermodynamic feasibility range for multicomponent distillation processes as well as for distillation trains and process-intensified solutions taking into account both product purity and product recovery specifications. The final product of this study is a thorough procedure to determine the flexibility boundaries of feed and product compositions as well as an immediate and intuitive graphical representation from a binary standard distillation column to a complex multicomponent dividing wall column application

Effective properties of non-aging linear viscoelastic and hierarchical composites are investigated via a three-scale asymptotic homogenization method. In this approach, we consider the assumption of a generalized periodicity in the different structural levels and their characterization through the so-called stratified functions. The expressions for the associated local and homogenized problems, and the effective coefficients are derived at each level of organization by using the correspondence principle and the Laplace-Carson transform. Considering isotropic components and a perfect contact at the interfaces between the constituents, analytical solutions, in the Laplace-Carson space, are found for the local problems and the effective coefficients are computed. An interconversion procedure between the effective relaxation modulus and the effective creep compliance is carried out for obtaining information about both viscoelastic properties. The numerical inversion to the original temporal space is also performed. Finally, we exploit the potential of the approach and study the overall properties of a hierarchical viscoelastic composite structure representing the dermis.

International audience; Biobased monomers derived from eugenol were copolymerized by emulsion polymerization to produce latexes for adhesive applications. Stable latexes containing ethoxy dihydroeugenyl methacrylate and ethoxy eugenyl methacrylate with high total solids content of 50 wt% were obtained and characterized. Latexes synthesis was carried out using a semi-batch process and latexes with particle diameters in the range of 159-178 nm were successfully obtained. Glass transition temperature values of the resulting polymers ranged between -32 and -28°C. Furthermore, tack and peel measurements confirmed the possibility to use these latexes in adhesive applications.

International audience; Maleimides are attractive systems for photopolymerize for two major reasons: (1) they follow a radical mechanism without requiring a photoinitiator and (2) their rate of polymerization corresponds similarly to acrylates, which are commonplace in the industry. In this work, bismaleimide polypropylene oxide was cured under UV light forming thin films. Their surface properties were modified by copolymerization them with fluorinated comonomers. To this goal, perfluoropolyalkylethers (PFPAEs) with maleimide groups were synthesized, varying their chain structure, their functionality degree and consequently their intrinsic viscosity. These PFPPAE comonomers were highlighted to segregate at the surface, assuring omniphobic properties and acting as a protective layer against oxygen inhibition. These phenomenon were observed even when added at a concentration ≤5% w/w with respect to the main polypropylene oxide monomer. XPS analyses confirmed the segregation of the fluorine atoms at the surface during the UV-curing process of the coatings.

International audience; The deactivation mechanism and methods to cope with the poisoning by SO2 of LaCoO3 perovskite-based NO oxidation catalyst were investigated. The LaCoO3 perovskite was synthesized by a sol-gel method and the fresh, sulphate-deactivated and regenerated catalysts were characterized by X-ray Diffraction, X-ray Photoelectron Spectroscopy, H2-and soot-Temperature Programmed Reduction, Temperature Programmed Desorption and Diffuse Reflectance Infrared Fourier Transform Spectroscopy. The SO2 poisoning strongly affected the NO oxidation activity. It was demonstrated that the deactivation mechanism proceeds in two stages: initially the active sites with basic character are blocked by SO3 and subsequently the lanthanum sulphate salts grow progressively on the surface and cobalt is unaffected. Above 500 °C, the surface bound sulphates become mobile and migrate into the bulk of the catalyst. Several prevention and regeneration methods were proposed and tested. By mixing the catalyst with Ca(OH)2 as an adsorbent nearly 50% of the original activity was retained. Regeneration by diesel soot was presented here for the first time, where the blocking oxygen can spill over to the soot oxidizing it and releasing the bound sulphur as SO2 and CO2. Furthermore, a facile regeneration method was explored by washing the deactivated catalyst to dissolve the small amounts of sulphates on the surface.

A green, efficient and stable solar cell based only on water and safe and cheap elements of the periodic table is proposed in this work, finally consolidating (also from a sustainability viewpoint) the concept of “artificial photosynthesis” studied for decades by the scientific community. The concept of dye-sensitized solar cells is re-proposed here with a metal-free organic dye, an iodine-based electrolyte in a 100% aqueous environment and a new cathode (cationic PEDOT) synthesized for the first time with the aim of inhibiting the repulsion between the anions of redox couples and the PEDOT:PSS matrix commonly used as the counter-electrode. This elegant setup leads to a record efficiency of 7.02%, the highest value ever obtained for a water-based solar cell and, in general, for a photovoltaic device free of both organic solvents and expensive/heavy metals., A new cationic PEDOT derivative inhibits repulsion phenomena within iodine-based electrolytes, boosting the efficiency of aqueous solar cells.

In this work, dense, porous, and, for the first time, functionally-graded bi-layer scaffolds with a cylindrical geometry were produced from a commercially available hydroxyapatite powder using the robocasting technique. The bi-layer scaffolds were made of a dense core part attached to a surrounding porous part. Subsequently, these bi-layer robocast scaffolds were joined with an outer shell of an antibacterial porous polymer layer fabricated by solvent casting/salt leaching techniques, leading to hybrid ceramic-polymer scaffolds. The antibacterial functionality was achieved through the addition of silver ions to the polymer layer. All the robocast samples, including the bi-layer ones, were first characterized through scanning electron microscopy observations, mechanical characterization in compression and preliminary bioactivity tests. Then, the hybrid bi-layer ceramic-polymer scaffolds were characterized through antimicrobial tests. After sintering at 1300 &deg, C for 3 h, the compressive strengths of the structures were found to be equal to 29 &plusmn, 4 MPa for dense samples and 7 &plusmn, 4 MPa for lattice structures with a porosity of 34.1%. Bioactivity tests performed at 37 &deg, C for 4 weeks showed that the precipitated layer on the robocast samples contained octacalcium phosphate. Finally, it was evidenced that the hybrid structure was effective in releasing antibacterial Ag+ ions to the surrounding medium showing its potential efficiency in limiting Staphylococcus aureus proliferation during surgery.

We present an overview of the main techniques for production and processing of graphene and related materials (GRMs), as well as the key characterization procedures. We adopt a 'hands-on' approach, providing practical details and procedures as derived from literature as well as from the authors' experience, in order to enable the reader to reproduce the results. Section I is devoted to 'bottom up' approaches, whereby individual constituents are pieced together into more complex structures. We consider graphene nanoribbons (GNRs) produced either by solution processing or by on-surface synthesis in ultra high vacuum (UHV), as well carbon nanomembranes (CNM). Production of a variety of GNRs with tailored band gaps and edge shapes is now possible. CNMs can be tuned in terms of porosity, crystallinity and electronic behaviour. Section II covers 'top down' techniques. These rely on breaking down of a layered precursor, in the graphene case usually natural crystals like graphite or artificially synthesized materials, such as highly oriented pyrolythic graphite, monolayers or few layers (FL) flakes. The main focus of this section is on various exfoliation techniques in a liquid media, either intercalation or liquid phase exfoliation (LPE). The choice of precursor, exfoliation method, medium as well as the control of parameters such as time or temperature are crucial. A definite choice of parameters and conditions yields a particular material with specific properties that makes it more suitable for a targeted application. We cover protocols for the graphitic precursors to graphene oxide (GO). This is an important material for a range of applications in biomedicine, energy storage, nanocomposites, etc. Hummers' and modified Hummers' methods are used to make GO that subsequently can be reduced to obtain reduced graphene oxide (RGO) with a variety of strategies. GO flakes are also employed to prepare three-dimensional (3d) low density structures, such as sponges, foams, hydro- or aerogels. The assembly of flakes into 3d structures can provide improved mechanical properties. Aerogels with a highly open structure, with interconnected hierarchical pores, can enhance the accessibility to the whole surface area, as relevant for a number of applications, such as energy storage. The main recipes to yield graphite intercalation compounds (GICs) are also discussed. GICs are suitable precursors for covalent functionalization of graphene, but can also be used for the synthesis of uncharged graphene in solution. Degradation of the molecules intercalated in GICs can be triggered by high temperature treatment or microwave irradiation, creating a gas pressure surge in graphite and exfoliation. Electrochemical exfoliation by applying a voltage in an electrolyte to a graphite electrode can be tuned by varying precursors, electrolytes and potential. Graphite electrodes can be either negatively or positively intercalated to obtain GICs that are subsequently exfoliated. We also discuss the materials that can be amenable to exfoliation, by employing a theoretical data-mining approach. The exfoliation of LMs usually results in a heterogeneous dispersion of flakes with different lateral size and thickness. This is a critical bottleneck for applications, and hinders the full exploitation of GRMs produced by solution processing. The establishment of procedures to control the morphological properties of exfoliated GRMs, which also need to be industrially scalable, is one of the key needs. Section III deals with the processing of flakes. (Ultra)centrifugation techniques have thus far been the most investigated to sort GRMs following ultrasonication, shear mixing, ball milling, microfluidization, and wet-jet milling. It allows sorting by size and thickness. Inks formulated from GRM dispersions can be printed using a number of processes, from inkjet to screen printing. Each technique has specific rheological requirements, as well as geometrical constraints. The solvent choice is critical, not only for the GRM stability, but also in terms of optimizing printing on different substrates, such as glass, Si, plastic, paper, etc, all with different surface energies. Chemical modifications of such substrates is also a key step. Sections IV–VII are devoted to the growth of GRMs on various substrates and their processing after growth to place them on the surface of choice for specific applications. The substrate for graphene growth is a key determinant of the nature and quality of the resultant film. The lattice mismatch between graphene and substrate influences the resulting crystallinity. Growth on insulators, such as SiO2, typically results in films with small crystallites, whereas growth on the close-packed surfaces of metals yields highly crystalline films. Section IV outlines the growth of graphene on SiC substrates. This satisfies the requirements for electronic applications, with well-defined graphene-substrate interface, low trapped impurities and no need for transfer. It also allows graphene structures and devices to be measured directly on the growth substrate. The flatness of the substrate results in graphene with minimal strain and ripples on large areas, allowing spectroscopies and surface science to be performed. We also discuss the surface engineering by intercalation of the resulting graphene, its integration with Si-wafers and the production of nanostructures with the desired shape, with no need for patterning. Section V deals with chemical vapour deposition (CVD) onto various transition metals and on insulators. Growth on Ni results in graphitized polycrystalline films. While the thickness of these films can be optimized by controlling the deposition parameters, such as the type of hydrocarbon precursor and temperature, it is difficult to attain single layer graphene (SLG) across large areas, owing to the simultaneous nucleation/growth and solution/precipitation mechanisms. The differing characteristics of polycrystalline Ni films facilitate the growth of graphitic layers at different rates, resulting in regions with differing numbers of graphitic layers. High-quality films can be grown on Cu. Cu is available in a variety of shapes and forms, such as foils, bulks, foams, thin films on other materials and powders, making it attractive for industrial production of large area graphene films. The push to use CVD graphene in applications has also triggered a research line for the direct growth on insulators. The quality of the resulting films is lower than possible to date on metals, but enough, in terms of transmittance and resistivity, for many applications as described in section V. Transfer technologies are the focus of section VI. CVD synthesis of graphene on metals and bottom up molecular approaches require SLG to be transferred to the final target substrates. To have technological impact, the advances in production of high-quality large-area CVD graphene must be commensurate with those on transfer and placement on the final substrates. This is a prerequisite for most applications, such as touch panels, anticorrosion coatings, transparent electrodes and gas sensors etc. New strategies have improved the transferred graphene quality, making CVD graphene a feasible option for CMOS foundries. Methods based on complete etching of the metal substrate in suitable etchants, typically iron chloride, ammonium persulfate, or hydrogen chloride although reliable, are time- and resource-consuming, with damage to graphene and production of metal and etchant residues. Electrochemical delamination in a low-concentration aqueous solution is an alternative. In this case metallic substrates can be reused. Dry transfer is less detrimental for the SLG quality, enabling a deterministic transfer. There is a large range of layered materials (LMs) beyond graphite. Only few of them have been already exfoliated and fully characterized. Section VII deals with the growth of some of these materials. Amongst them, h-BN, transition metal tri- and di-chalcogenides are of paramount importance. The growth of h-BN is at present considered essential for the development of graphene in (opto) electronic applications, as h-BN is ideal as capping layer or substrate. The interesting optical and electronic properties of TMDs also require the development of scalable methods for their production. Large scale growth using chemical/physical vapour deposition or thermal assisted conversion has been thus far limited to a small set, such as h-BN or some TMDs. Heterostructures could also be directly grown. Section VIII discusses advances in GRM functionalization. A broad range of organic molecules can be anchored to the sp 2 basal plane by reductive functionalization. Negatively charged graphene can be prepared in liquid phase (e.g. via intercalation chemistry or electrochemically) and can react with electrophiles. This can be achieved both in dispersion or on substrate. The functional groups of GO can be further derivatized. Graphene can also be noncovalently functionalized, in particular with polycyclic aromatic hydrocarbons that assemble on the sp 2 carbon network by π–π stacking. In the liquid phase, this can enhance the colloidal stability of SLG/FLG. Approaches to achieve noncovalent on-substrate functionalization are also discussed, which can chemically dope graphene. Research efforts to derivatize CNMs are also summarized, as well as novel routes to selectively address defect sites. In dispersion, edges are the most dominant defects and can be covalently modified. This enhances colloidal stability without modifying the graphene basal plane. Basal plane point defects can also be modified, passivated and healed in ultra-high vacuum. The decoration of graphene with metal nanoparticles (NPs) has also received considerable attention, as it allows to exploit synergistic effects between NPs and graphene. Decoration can be either achieved chemically or in the gas phase. All LMs, can be functionalized and we summarize emerging approaches to covalently and noncovalently functionalize MoS2 both in the liquid and on substrate. Section IX describes some of the most popular characterization techniques, ranging from optical detection to the measurement of the electronic structure. Microscopies play an important role, although macroscopic techniques are also used for the measurement of the properties of these materials and their devices. Raman spectroscopy is paramount for GRMs, while PL is more adequate for non-graphene LMs (see section IX.2). Liquid based methods result in flakes with different thicknesses and dimensions. The qualification of size and thickness can be achieved using imaging techniques, like scanning probe microscopy (SPM) or transmission electron microscopy (TEM) or spectroscopic techniques. Optical microscopy enables the detection of flakes on suitable surfaces as well as the measurement of optical properties. Characterization of exfoliated materials is essential to improve the GRM metrology for applications and quality control. For grown GRMs, SPM can be used to probe morphological properties, as well as to study growth mechanisms and quality of transfer. More generally, SPM combined with smart measurement protocols in various modes allows one to get obtain information on mechanical properties, surface potential, work functions, electrical properties, or effectiveness of functionalization. Some of the techniques described are suitable for 'in situ' characterization, and can be hosted within the growth chambers. If the diagnosis is made 'ex situ', consideration should be given to the preparation of the samples to avoid contamination. Occasionally cleaning methods have to be used prior to measurement., We acknowledge funding from the European Commission Graphene Flagship Core1 (grant agreement 696656) and Core2 (grant agreement 785219).

International audience; A new photoactivable material based on polyethylene imine with allyl functions (A-PEI monomer) was synthesized to develop new hydrogel. The water-based photoinitiating system consisting of anthraquinone-2-sulfonic acid (AQS) and N-methyldiethanol amine (MDEA) was studied by laser flash photolysis and electron paramagnetic resonance. LED@385 nm exposure of this combination of AQS with MDEA in aqueous medium has led to the formation of -aminoalkyl radicals which were able to cross-link the acrylamide and A-PEI to generate new antibacterial materials in reduced time and under air. Interestingly, the addition of the multifunctional A-PEI monomer to acrylamide derived monomers has led to faster gel formation and an increase of the instantaneous G' modulus value. The resulting hydrogel containing quaternary ammonium groups on its surface has demonstrated excellent anti-adherence and biocide properties against Escherichia coli and Staphylococcus aureus.

International audience; We formalize the coupled criterion (CC) in the framework of Finite Fracture Mechanics (FFM) to take into account the material nonlinear behavior. Once the true stress–strain curve is recorded, we estimate the Ramberg–Osgood (RO) parameters. We then exploit these values in the FFM numerical implementation, considering both an average stress requirement and the energy balance. As a case study, we consider experimental data on Brazilian disks containing a circular hole and involving two materials — PMMA and GPPS. The computational effort of the analysis increases with respect to the linear elastic case, but keeps reasonable. On the other hand, the nonlinear FFM investigation allows a significant improvement of the failure stress predictions, especially those related to smaller holes corresponding to a more pronounced nonlinear behavior detected during tests.

International audience; Carbon Nitride and its polymorphs have recently gained large interests for their huge properties and applications in different fields, from lighting to photocatalysis. Further, several attempts were recently devoted to tune and control its optical and electrical properties. In this report we analyze phenyl modified Carbon Nitride structures obtained by simple thermal polymerization at different temperatures (250-400°C) of the starting precursor: 2,4-diamino-6-phenyl-1,3,5-triazine. A multi-technique experimental data (XRD patterns, Raman, TGA and DTG, steady-time and time resolved Luminescence, Photoluminescence Excitation spectra, Reflectivity spectra) was applied to analyze the relationship between structural and optical properties and to give more insight on the effect of synthesis procedure on the final polymer. The optical properties evidenced an interesting shift towards the visible region of the absorption spectrum of the phenyl modified g-C 3 N 4 polymer that, associated with the high optical quantum yield (about 60%) and to a broad emission in the green-red spectral region, makes the samples very suitable for lighting applications. Indeed, we report a first prototype of white LED emission by assembly of a commercial blue LED and the Phenyl modified g-C 3 N 4 powders as phosphor, verifying the structural and optical stability over about 10,000 working hours.

International audience; Biobased monomers have been used to replace their petroleum counterparts in the synthesis of polymers that are aimed at different applications. However, environmentally friendly polymerization processes are also essential to guarantee greener materials. Thus, photoinduced polymerization, which is low-energy consuming and solvent-free, rises as a suitable option. In this work, eugenol-, isoeugenol-, and dihydroeugenol-derived methacrylates are employed in radical photopolymerization to produce biobased polymers. The polymerization is monitored in the absence and presence of a photoinitiator and under air or protected from air, using Real-Time Fourier Transform Infrared Spectroscopy. The polymerization rate of the methacrylate double bonds was affected by the presence and reactivity of the allyl and propenyl groups in the eugenol-and isoeugenol-derived methacrylates, respectively. These groups are involved in radical addition, degradative chain transfer, and termination reactions, yielding crosslinked polymers. The materials, in the form of films, are characterized by differential scanning calorimetry, thermogravimetric, and contact angle analyses.

Perfluoropolyalkylether (PFPAE) reactive macromers can be used in very low concentration (≤2 wt%) as efficient surface modifying agents of epoxy resins to obtain hydrophobic photocured copolymers. However, the hydrophobicity achieved thanks to the spontaneous migration of the PFPAE chains to the free surface could be dramatically lost due to environmentally induced rearrangements of the fluorinated segments, even though they are chemically bonded to the polymer matrix. To preserve the coating performances of the photocured copolymers when exposed to various environments, different approaches have been investigated. In particular, to hinder the mobility of the fluorinated chains, the length of the fluorinated comonomer chain, the epoxy matrix stiffness, and the functional PFPAE end-groups have been tuned. Such strategies are demonstrated to inhibit or completely suppress the surface reconstruction of the copolymers when exposed to different surrounding environments (e.g., immersion in water or oil), allowing to obtain photocured films with a long-term and constant reduced surface energy of ≈20 mN/m.

International audience; The simulation of bubble columns operating under the heterogeneous regime is an ambitious challenge, due to the difficulty of predicting accurately hy-drodynamics and bubble size distributions, that requires experimental data for model validation. Gas fraction distributions, liquid and gas velocity profiles and bubble size distributions across bubble columns are deeply interconnected in these systems and only a comprehensive study allows the links between them to be understood. This work reports experimental data obtained by measuring bubble sizes with an innovative technique based on the cross correlation between two optical probes. Particular attention is given to the role of additives and impurities with a view to suppressing bubble coalescence. Initially experiments are carried out with demineralized water; subsequently they are repeated with tap water and adding small quantities of ethanol. Results show that contaminants and alcohol addition suppress bub-* (A. Cloupet), daniele.marchisio@polito.it (D.L. Marchisio) ble coalescence and induces a decrease of mean bubble sizes. Furthermore, alcohol addition delays the transition from homogeneous to heterogeneous regimes and increases the gas holdup under the heterogeneous regime. Gas distribution is studied through two different perforated spargers. Changing the sparger it is possible to modify the bubble size in the lowest part of the column significantly. A perforated sparger with big holes causes the formation of big bubbles close to the holes of the sparger and promotes bubble breakage in the lower part of the column. By combining ethanol addition and sparger modification, bubble coalescence and bubble breakage can be decoupled in a controlled manner and interesting conclusions concerning these processes can be drawn. Beyond the novelty of bubble size measurements at high gas fraction , the experimental data collected are very useful to validate and develop computational fluid dynamics simulations coupled with population balance models suitable for heterogeneous bubbly flows.

International audience; Consolidated granular materials and materials with damage at the microstructural level exhibit anomalous elastic behavior even when excited by low-amplitude elastic waves. Their response is given by a combination of slow- and fast-dynamics effects which, as their definition implies, act on very different time scales. In particular, conditioning (a transition to an elastic state dependent on the strain amplitude) and relaxation (full recovery of the elastic properties when the strain is removed) have been observed in different materials and under different dynamic excitations. An experimental parametric analysis of the phenomenon, aiming to establish correlations between the effects on different elastic physical properties (wave velocity and attenuation coefficient) and between the evolution of conditioning and relaxation is proposed here, with the goal of better characterizing slow dynamics and allowing one to go beyond the phenomenological description of elastic hysteresis currently available. At the same time, by studying different materials, we wish to highlight the possibility of using slow dynamics as an additional tool for materials characterization.

Nanocellulose was extracted from short bast fibers, from hemp (Cannabis Sativa L.) plants harvested at seed maturity, non-retted, mechanically decorticated in a defibering apparatus giving non-aligned fibers. A chemical pretreatment with NaOH and HCl allowed the removal of most of the non-cellulosic components of the fibers. No bleaching was performed. The chemically pretreated fibers were then refined in a beater and treated with a cellulase enzyme, before the mechanical defibrillation in an ultrafine friction grinder. The fibers were characterized by microscopy, infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction after each step of the process, to understand the evolution of their morphology and composition. The obtained nanocellulose suspension was composed of rod-like fibrils with widths of 5-12 nm, stacks of nanofibrils with widths of 20-200 nm, and some larger fibers. The crystallinity index was found to increase from 74% for the raw fibers to 80% for the nanocellulose. The nanocellulose retained a yellowish color indicating the presence of some residual lignin. Properties of nanopaper prepared with the hemp nanocellulose were similar to those of nanopapers prepared with wood pulp derived rod-like nanofibrils., 37 pages, 19 figures, including supplementary information (SI)

International audience; Photochromic materials are attractive for the development of holograms for different reasons: they show a modulation of the complex refractive index, meaning they are suitable for both amplitude and phase holograms; they are self-developing materials, which do not require any chemical process after the light exposure to obtain the final hologram; the holograms are rewritable, making the system a convenient reconfigurable platform for these types of diffractive elements. In this paper, we will show the features of photochromic materials, in particular diarylethenes in terms of the modulation of a transparency and refractive index, which are mandatory for their use in holography. Moreover, we report on the strategies used to write binary and grayscale holograms and their achieved results. The outcomes are general, and they can be further applied to other classes of photochromic materials in order to optimize the system for achieving high efficiency and high fidelity holograms.

Bio-based coatings were obtained by the layer-by-layer (LbL) technique from a native chitosan (Mw ≈ 30,000 g mol−1) or from two synthesized phosphorylated chitosan of different molecular weights (Mw ≈ 30,000 g mol−1 and Mw ≈ 250,000 g mol−1) combined with alginate and used for corrosion protection of an aluminum alloy (AA) 3003. First, the LbL growth was monitored by Fourier transform infrared spectroscopy on silicon wafers. Cross-sections of Si wafers were examined by scanning electron microscopy allowing the films thickness to be measured. With the native chitosan and in the presence of 10 bilayers, the LbL thickness was about 200 nm, whereas it was about 300 nm with the phosphorylated chitosan of low molecular weight and about 500 nm with the phosphorylated chitosan of high molecular weight. Then, the bio-based coatings were deposited on the AA3003 by the LbL technique and their protective properties were evaluated by electrochemical impedance spectroscopy (EIS) during immersion in a 0.1 M Na2SO4 solution. It was shown that the three LbL coatings improved the corrosion resistance of the AA3003. The resistance values, extracted at low frequency on the impedance diagrams were attributed to the resistance of the aluminum oxide layer (Rox). The Rox values were at least two orders of magnitude higher for the coated samples (108 Ω cm2) compared to the uncoated one (5 105 Ω cm2). There was no significant difference between the different LbL coatings, which mainly acted by decreasing the active surface area and have a limited barrier effect.

International audience; We report the radiation grafting of bis[2-(methacryloyloxy)ethyl] phosphate (B2MP) through electron-beam onto PVDF films and through swift heavy ions (SHI) irradiations into the pores of track-etched PVDF membranes. Radiolytically produced radicals were studied using EPR. To adapt the radiation grafting protocol inside the nanopores of track-etched membranes, the electron-beam irradiated films at varying monomer concentrations, doses and solvent mixtures were first studied. It was found that track-etched membranes, even after 1 h of chemical treatment, do not require a post-etching irradiation to initiate free-radical polymerization of B2MP from remaining radiationinduced radicals. The presence of functional groups inside the nanopores of the membrane were examined using FTIR and XPS. After exposure of B2MP-g-PVDF membranes to a uranyl solution, XPS was also exploited to evidence of O2UO22+ trapping inside the membrane nanoporosity by tracking the presence of U 4f peak. The B2MP-g-PVDF membranes were converted into electrodes by depositing 35 nm of gold on each side through a mask. Detection of ppb concentrations (from 20 to 100 ppb) of uranyl by B2MP-g-PVDF membrane electrodes was demonstrated by means of square wave cathodic stripping voltammetry (SW-CSV). The limit of detection (LOD) was estimated to be 17 ppb (3σ−/ slope).

Here it is proposed a discussion concerning the earliest researches on the liquid crystals. The discussion is based on a book published in 1911, written by Alfred Tutton. In this book, we find described the instrument which was fundamental for observing the mesophases of thermotropic liquid crystals, the “crystallisation microscope”, that Otto Lehmann built for his studies on crystals. It consisted of a polarized-light microscope, equipped by heating and cooling systems for the control of temperature. This experimental set-up allowed Lehmann to study the cholesteryl benzoate, the first material that was discovered by Friedrich Reinitzer as exhibiting a mesophase. In the following years, many other materials were prepared for Lehmann’s studies. In the Tutton’s book, among the chemists who prepared the samples, we can find mentioned Ludwig Gattermann and Daniel Vorländer. We can find also the Vorländer‘s “recipes” to obtain liquid crystalline materials, those which have rod-like molecules.&nbsp

Open Access in Zenodo; To have a polymer dispersed liquid crystal (PDLC), the liquid crystalline material is dispersed into a liquid polymer. When the polymer changes from liquid to solid, the liquid crystal becomes incompatible with the polymer and creates dispersed droplets throughout the polymeric film. The film can be processed by standard techniques to have large and environmentally robust displays and light shutters. This paper describes PDLC films and their properties in a simplified approach, suitable for teaching the devices based on such films to students of university courses.

The use of biobased monomers in emulsion polymerization arises as an attractive option for the synthesis of green polymers. Eugenol, a naturally occurring phenol that is currently mainly produced from clove oil but could also be obtained by depolymerization of lignin, is an interesting molecule for the preparation of biobased monomers and polymers. Readily polymerizable functional groups can be easily introduced into its chemical structure through modification of the phenol group. In the present work, eugenol-based methacrylates have been used as monomers in emulsion radical polymerization with different initiation systems. Stable latexes of poly(ethoxy dihydroeugenyl methacrylate), poly(ethoxy eugenyl methacrylate) and poly(ethoxy isoeugenyl methacrylate) with particle diameter size in the 45–71 nm range were successfully obtained. Glass transition temperatures of the resulting polymers ranged between 20 and 72 °C. This study opens the way to the use of these new biobased monomers into latexes formulatio...

This study deals with the problem of the least-weight design of a lattice structure subject to constraints of different nature. To face this problem, a general multi-scale optimisation procedure is proposed. This approach aims at optimising both global and local geometric parameters defining the shape of the representative volume element of the lattice at the mesoscopic scale. The optimisation procedure involves design requirements defined at different scales: geometric and manufacturing constraints are involved at the mesoscopic scale, whilst thermodynamic constraints on the positive definiteness of the stiffness tensor of the lattice (modelled as an equivalent homogeneous anisotropic medium) intervene at the macroscopic scale. Finally, since lattice structures usually undergo compressive loads, a requirement on the first local buckling load is considered too. The proposed approach is based on (a) the non-uniform rational basis splines curves theory to describe the shape of the struts composing the lattice, (b) the strain energy homogenisation technique of periodic media to perform the scale transition and (c) a special genetic algorithm to perform optimisation calculations. The optimised solutions provided by the presented method are characterised by a weight saving of about $$39\%$$ with slightly enhanced mechanical properties when compared to conventional octahedral lattice structures.

Computer Generated Holograms (CGHs) are used for wavefront shaping and complex optics testing. Present technology allows for recording binary CGHs. We propose a Digital Micro-mirror Device (DMD) as a reconfigurable mask, to record rewritable binary and grayscale CGHs on a photochromic plate. Opaque at rest, this plate becomes transparent when it is illuminated with visible light. We have successfully recorded the very first amplitude grayscale Fresnel CGH, with a contrast greater than 50, which was reconstructed with a high fidelity in shape, intensity, size and location. We propose a new Fourier CGH coding scheme leading to a quantification exceeding 1000 within a smaller cell size of 2x2 pixels. This code has been implemented for the BATMAN-instrument logo for visiting very different spatial frequencies. The CGH is recorded with our DMD-based set-up, leading to a 1000x1000 pixels hologram written on a photochromic plate. The reconstruction of the recorded images with a 632.8nm He-Ne laser beam and an imaging lens leads to images with a perfect fidelity in shape and intensity, for any single pixel of the original object. Our proposed code exhibits a much higher resolution, a better compacity and an increased throughput, in comparison with the current Fourier CGHs. These results reveal the high potential of this method for generating programmable/rewritable CGHs.

cited By 2; International audience; Scaffolds for bone tissue engineering require a combination of bioactivity and bioresorption at the sample surface and high mechanical properties in the bulk. This work presents a novel calcium phosphate (CaP)/polycaprolactone (PCL) scaffold with graded composition and porosity fraction. The scaffold is made of (i) a dense hydroxyapatite (HA)/β-tricalcium phosphate (β-TCP) core, (ii) a macroporous HA/β-TCP transition layer and (iii) a macroporous PCL/(HA/β-TCP) external layer. The ceramic layers were fabricated by gel-casting whereas the outer composite layer was obtained by a solvent casting/particle leaching process. The microstructure, phase composition and biodegradation of the scaffolds were characterized. The gradient of porosity was clearly obtained whereas the gradation of phase composition was less pronounced. An in vitro dissolution test was performed by immersing the scaffolds in a TRIS solution. The results showed a dissolution phenomenon with possible differentiated mechanisms in the different layers, in relation with the targeted multi-functionality. © 2018 Elsevier B.V.

We investigate the non-equilibrium behavior of a fully-connected (or all-to-all coupled) Bose-Hubbard model after a Mott to superfluid quench, in the limit of large boson densities and for an arbitrary number $V$ of lattice sites, with potential relevance in experiments ranging from cold atoms to superconducting qubits. By means of the truncated Wigner approximation, we predict that crossing a critical quench strength the system undergoes a dynamical phase transition between two regimes that are characterized at long times either by an inhomogeneous population of the lattice (i.e. macroscopical self-trapping) or by the tendency of the mean-field bosonic variables to split into two groups with phase difference $\pi$, that we refer to as $\pi$-synchronization. We show the latter process to be intimately connected to the presence, only for $V \ge 4$, of a manifold of infinitely many fixed points of the dynamical equations. Finally, we show that no fine-tuning of the model parameters is needed for the emergence of such $\pi$-synchronization, that is in fact found to vanish smoothly in presence of an increasing site-dependent disorder, in what we call a synchronization crossover., Comment: 22 pages, 8 figures; added explicit reference to the Truncated Wigner Approximation; added references; improved formatting

International audience; Concrete and consolidated granular media in general exhibit a strong nonlinearhysteretic elastic behavior when excited by ultrasonic wave perturbations. Due tothe sensitivity of their elastic properties to the small changes that can appear in theirmicrostructure, the dynamic stress-strain relationship considered at low strains isaffected by the presence of microcracks and hence the progression of damage.Tracking the nonlinear behavior can be made through the dependence on theexcitation amplitude of the amplitude of higher order harmonics or of the resonancefrequency of the sample. The present chapter shows a time domain analysis ofelastic nonlinearity based on the break of the superposition principle whenultrasonic continuous waves are propagating in concrete samples. The latter, whichcan be of different microstructures (grain sizes, mortar, or polymer matrix), helpsto understand the physical mechanisms involved in the different nonlinear elasticresponses.

https://ars-els-cdn-com.ezpum.biu-montpellier.fr/content/image/1-s2.0-S0300944018310099-mmc1.pdf; International audience; Perfluoropolyalkylether (PFPAE) structures can be functionalized with alcoholic groups using an appropriate synthetic pathway: these new fluorinated alcohols can be used as surface modifying agents, through chain transfer mechanism in cationic UV-curing of an epoxy system. Notwithstanding their very low concentration (only ≤5 wt%), the fluorinated alcohols are able to induce a dramatic improvement to the surface properties of the films, without substantially modifying their curing conditions and their bulk properties, neither their transparency. As confirmed by Fourier Transform-Infra Red (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) measurements, the fluorinated comonomers tend to concentrate selectively at the outermost layer of the epoxy UV-cured coatings, by spontaneously migrating to the free surface due to their low surface tension. The surface modification of the films depends on the concentration of the fluoroalcohols: coatings prepared with a concentration of PFPAE comonomer higher than 2 wt% are both hydrophobic and oleophobic. Moreover, thanks to their low surface energy (as low as 17 mN m−1) and reduced sliding angle (as low as 5°), photocured fluorinated copolymers show advanced coating performances such as anti-stain and self-cleaning properties.

International audience; Precise knowledge of the dependence of elastic modulus and Q factor on the amplitude of excitation is a prerequisite for the development and validation of models to explain the hysteresis observed in qua-sistatic experiments for various media, i.e., the different deformations at the same applied stress observed when stress change rate is positive or negative. Separation of different contributions to dynamic nonlin-earity (e.g., those due to nonequilibrium effects, often termed conditioning) and independent estimation of nonlinearities originated by the strain dependence of velocity and the damping factor are required, which is often not possible with standard approaches. Here we propose and validate a method that, measuring the response of a sample to a monochromatic excitation at different amplitudes, allows fast, continuous, and quasi-real-time monitoring of the dependence of the material elastic properties on amplitude: dynamic elastic modulus (related with velocity through density) and Q factor of the mechanical resonances (related with wave-amplitude attenuation parameters).

International audience

International audience; Solar Domestic Hot Water (SDHW) systems represent a constantly evolving technology in today's applications. With the new directives promoted by the European Union the renewable energy share produced in buildings will tend to increase further. Research on how to increase the efficiency of the thermal production from renewable energy are therefore of the foremost importance. This study aims to investigate the energy performance of an integral collector storage (ICS) prototype for DHW production. This ICS represents a new concept technology, integrating inside the same device a flat plate absorber and a storage section with phase change material (PCM) connected by heat pipes filled with methanol. An objective of this study was to investigate a possible alternative to conventional solar systems, with the aim of reducing investment costs and improving system reliability without compromising energy performance. The energy assessment was carried out using a numerical model in the Engineering Equation Solver (EES) environment, following an electrical analogy scheme. After a validation process by means of experimental data, a yearly simulation was launched in order to estimate the productivity and the solar fraction of the prototype. The results obtained allowed a global energy evaluation and a comparison with similar systems and to identify the pros and cons of this new technology.