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Gene expression consists in the synthesis of proteins from the information encoded on DNA. One of the two main steps of gene expression is the translation of messenger RNA (mRNA) into polypeptide sequences of amino acids. Here, by taking into account mRNA degradation, we model the motion of ribosomes along mRNA with a ballistic model where particles advance along a filament without excluded volume interactions. Unidirectional models of transport have previously been used to fit the average density of ribosomes obtained by the experimental ribo-sequencing (Ribo-seq) technique. In this case an inverse fit gives access to the kinetic rates: the position-dependent speeds and the entry rate of ribosomes onto mRNA. The degradation rate is not, however, accounted for and experimental data from different experiments are needed to have enough parameters for the fit. Here, we propose an entirely novel experimental setup and theoretical framework consisting in splitting the mRNAs into categories depending on the number of ribosomes from one to four. We solve analytically the ballistic model for a fixed number of ribosomes per mRNA, study the different regimes of degradation, and propose a criteria for the quality of the inverse fit. The proposed method provides a high sensitivity to the mRNA degradation rate. The additional equations coming from using the monosome (single ribosome) and polysome (arbitrary number) ribo-seq profiles enable us to determine all the kinetic rates in terms of the experimentally accessible mRNA degradation rate., 10 pages, 7 figures, 2 tables

Polycomb (Pc) group proteins are transcriptional regulators with key roles in development, cell identity and differentiation. Pc-bound chromatin regions form repressive domains that interact in 3D to assemble repressive nuclear compartments. Here, we used multiplexed chromatin imaging to investigate whether Pc compartments involve the clustering of multiple Pc domains during Drosophila development. Notably, 3D proximity between Pc targets is rare and involves predominantly pairwise interactions. These 3D proximities are particularly enhanced in segments where Pc genes are co-repressed. In addition, segment-specific expression of Hox Pc targets leads to their spatial segregation from Pc repressed genes. Finally, non-Hox Pc targets are proximal in regions where they are co-expressed. These results indicate that long-range Pc interactions are temporally and spatially regulated during differentiation and development but do not involve clustering of multiple distant Pc genes.

As compared to other techniques of analysis of nanostructures, small-angle neutron scattering has always been way better in terms of design of special contrast situations, and worse for statistics due to inherently low flux. SANS beamlines at ILL, and in particular D11 dedicated to soft matter studies, have allowed to keep the first advantage, while providing excellent experimental conditions respect to, including with respect to flux.In this talk, I will present some recent studies of polymer structure in nanocomposites. Such materials have striking mechanical and dynamical properties, in particular the dynamics of the polymer close to the nanoparticles has triggered a large body of experimental and theoretical studies. The possible slow-down of the polymer corresponds to higher moduli, and the percolation of any hard phase, particles or slowed-down polymer, has a strong impact on the macroscopic mechanical properties. If one wishes to specifically characterize the structure of the polymer, SANS is one of the best options. By blending hydrogenated and deuterated chains, while matching the filler silica nanoparticles, we have recently provided evidence for chain-mass dependent bulk or interfacial segregation, and modelling and experimental results will be critically reviewed. In a second study, we have characterized the particle dispersion by small-angle scattering and reverse Monte Carlo modelling, and used it to improve the determination of the thickness of the polymer interfacial layer seen by broadband dielectric spectroscopy. Both the general nanoparticle dispersion and the characteristic time of this interfacial layer has been shown to be tunable by surface modification, paving the way for a precise control of mechanical properties of polymer nanocomposites in the future.

International audience; Gene expression consists in the synthesis of proteins from the information encoded on DNA. One of the two main steps of gene expression is the translation of messenger RNA (mRNA) into polypeptide sequences of amino acids. Here, by taking into account mRNA degradation, we model the motion of ribosomes along mRNA with a ballistic model where particles advance along a filament without excluded volume interactions. Unidirectional models of transport have previously been used to fit the average density of ribosomes obtained by the experimental ribosome sequencing (Ribo-Seq) technique. In this case an inverse fit gives access to the kinetic rates: the position-dependent speeds and the entry rate of ribosomes into mRNA. The degradation rate is not, however, accounted for and experimental data from differentexperiments are needed to have enough parameters for the fit. Here, we propose an entirely novel experimental setup and theoretical framework consisting in splitting the mRNAs into categories depending on the number of ribosomes from one to four. We analytically solve the ballistic model for a fixed number of ribosomes per mRNA, study the different regimes of degradation, and propose a criterion for the quality of the inverse fit. The proposed method provides a high sensitivity to the mRNA degradation rate. The additional equations coming from using the monosome (single ribosome) and polysome (arbitrary number) Ribo-Seq profiles enables us to determine all the kinetic rates in terms of the experimentally accessible mRNA degradation rate.

The value of MR radiomic features at a microscopic scale has not been explored in ovarian cancer. The objective of this study was to probe the associations of MR microscopy (MRM) images and MRM-derived radiomic maps with histopathology in high-grade serous ovarian cancer (HGSOC). Nine peritoneal implants from 9 patients with HGSOC were imaged ex vivo with MRM using a 9.4-T MR scanner. All MRM images and computed pixel-wise radiomics maps were correlated with the slice-matched stroma and tumor proportion maps derived from whole histopathologic slide images (WHSI) of corresponding peritoneal implants. Automated MRM-derived segmentation maps of tumor and stroma were constructed using holdout test data and validated against the histopathologic gold standard. Excellent correlation between MRM images and WHSI was observed (Dice index = 0.77). Entropy, correlation, difference entropy, and sum entropy radiomic features were positively associated with high stromal proportion (r = 0.97,0.88, 0.81, and 0.96 respectively, p < 0.05). MR signal intensity, energy, homogeneity, auto correlation, difference variance, and sum average were negatively associated with low stromal proportion (r = -0.91, -0.93, -0.94, -0.9, -0.89, -0.89, respectively, p < 0.05). Using the automated model, MRM predicted stromal proportion with an accuracy ranging from 61.4% to 71.9%. In this hypothesis-generating study, we showed that it is feasible to resolve histologic structures in HGSOC using ex vivo MRM at 9.4 T and radiomics.

International audience; Rubber-based nanocomposites prepared by solid-phase mixing with precipitated silica nanoparticles are typically stronglyaggregated systems with different levels of spatial organization, as highlighted by our group in the past [1]. The strategythat we developed these past years was to investigate such systems based on the study of simplified industrial sampleswith ingredients limited to a strict minimum. The analysis of small-angle X-ray scattering data can then be performed onthe scale of a micrometric simulation box. Tens of thousands of “model” nanoparticles are embedded in the matrix, andtheir dispersion strongly affects both the mechanical properties of the material, and the scattered intensity. A statisticalmethod based on a reverse Monte Carlo solution of this many-parameter scattering problem will be presented, showingthat some key features like percolation can be described [2].Another key feature of rubber nanocomposites refers to the influence of the filler surfaces on the polymer structure anddynamics, and some recent progress will be discussed [3]. In particular, we have studied blends of short and long chains,where one chain type is deuterated, by small-angle neutron scattering. Different degrees of spatial segregation could beidentified recently, including a peculiar, “fish-shaped” interfacial gradient characterized also by reverse Monte Carlosimulations, this time of the interface.[1] Guilhem P. Baeza, Anne-Caroline Genix, C. Degrandcourt, Laurent Petitjean, Jérémie Gummel, Marc Couty, Julian Oberdisse, Macromolecules 2013, 46, 317−329(cover article)[2] Musino D, Genix A-C, Chauveau E, Bizien T, Oberdisse J, Nanoscale 2020, 12:3907.[3] A.C. Genix, V. Bocharova, B. Carroll, P. Dieudonné-George, M. Sztucki, R. Schweins, A. P. Sokolov, and Julian Oberdisse, ACS Applied Materials and Interfaces,2021, in press

International audience; We report the measurement of the interaction energy between a charged Brownian polystyrene particle and an air–water interface. The interaction potential is obtained from the Boltzmann equation by tracking particle interface distance with a specifically designed Dual-Wave Reflection Interference Microscopy (DW-RIM) setup. The particle has two equilibrium positions located at few hundreds of nanometers from the interface. The farthest position is well accounted by a DLVO model complemented by gravity. The closest one, not predicted by current models, more frequently appears in water solutions at relatively high ions concentrations, when electrostatic interaction is screened out. It is accompanied by a frozen rotational diffusion dynamics that suggests an interacting potential dependent on particle orientation and stresses the decisive role played by particle surface heterogeneities. Building up on both such experimental results, the important role of air nanobubbles pinned on the particle interface is discussed.

In rhythmical movement performance, our brain has to sustain movement while correcting for biological noise-induced variability. Here, we explored the functional anatomy of brain networks during voluntary rhythmical elbow flexion/extension using kinematic movement regressors in fMRI analysis to verify the interest of method to address motor control in a neurological population. We found the expected systematic activation of the primary sensorimotor network that is suggested to generate the rhythmical movement. By adding the kinematic regressors to the model, we demonstrated the potential involvement of cerebellar-frontal circuits as a function of the irregularity of the variability of the movement and the primary sensory cortex in relation to the trajectory length during task execution. We suggested that different functional brain networks were related to two different aspects of rhythmical performance: rhythmicity and error control. Concerning the latter, the partitioning between more automatic control involving cerebellar-frontal circuits versus less automatic control involving the sensory cortex seemed thereby crucial for optimal performance. Our results highlight the potential of using co-registered fine-grained kinematics and fMRI measures to interpret functional MRI activations and to potentially unmask the organisation of neural correlates during motor control.

National audience; Hard and soft proteins at fluid interfaces

National audience; Les techniques de microrhéologie basées sur le suivi optique de particules microniques sont très intéressantes lorsqu’il s’agit de mesurer les propriétés viscoélastiques de fluides complexes de petit volume. Elles peuvent également paraître très intéressantes pour sonder localement des milieux hétérogènes. Dans le cas de milieux anisotropes comme les cristaux liquides nématiques, ces techniques doivent cependant être utilisées avec précaution. Nous l’illustrerons à travers le cas d’un cristal liquide lyotrope, le cromoglycate de sodium (DSCG) pour lequel nous avons examiné la pertinence des données rhéologiques extraites à partir de la dynamique de microparticules.Le mouvement Brownien, inhabituel, de microsphères dans la phase nématique de ce système avait en effet attiré récemment l’attention [1,2] suggérant un couplage complexe entre les fluctuations du directeur et les fluctuations de positions des billes. Bien qu’il ait été récemment proposé que des mesures par suivi de particules puissent être utilisées pour obtenir les différentes viscosités de la phase nématique [3], ce phénomène peut en effet conduire à des mesures rhéologiques incohérentes. Afin d’explorer ces différents problèmes, nous avons étudié le mouvement Brownien de particules dans des échantillons alignés en cellules minces (épaisseur 50µm) tout en variant à la fois la concentration de DSCG et la taille des particules (0.5, 1, 3, and 6µm de diamètre).Des propriétés viscoélastiques effectives ont été extraites de nos mesures de microrhéologie passive ainsi que de mesures actives basées sur l’utilisation de pinces optiques et le mouvement forcé des particules[4]. Nos résultats expliquent pourquoi différents comportements viscoélastiques ont été obtenus précédemment sur ce même système et l’origine des modules élastiques mesurés.

International audience; L’existence d’une phase « Nematique twist Bend » (NTB) a été prédite par I.Dozov dès 2001 [1] mais n’a été observée expérimentalement qu’en 2010 [2]. Cette phase est assez originale car elle présente optiquement des défauts de type coniques focales sans réel ordre translationnel observable en diffusion des rayons X. Généralement cette phase est présente à des températures élevées (au-dessus de 100°C) dans les corps purs. L’ajout d’un nématogène [comme le 4-Cyano-4'-pentylbiphenyl (5CB)] à un composé NTB [tels que le 1,7-bis (4-cyanobiphényl-4-yl) heptane (CB7CB)] permet de diminuer fortement la plage d’existence de la phase NTB [3] tout en modifiant continûment les propriétés thermiques et diélectriques. Dans ce travail, nous avons exploré les modifications dues à l’ajout au CB7CB de smectogènes, et en particulier du 4′-octyl-4-biphénylcarbonitrile (8CB). Le diagramme de phase de ce dernier mélange binaire présente des caractéristiques surprenantes. Malgré leur ressemblance macroscopique, les phases SmA et NTB semblent ainsi incompatibles et restent séparées par une phase nématique s’étendant à très basse température (-20 ° C) pour une fraction CB7CB de ϕ_c≈20%. Nous avons par ailleurs caractérisé les propriétés optiques, thermiques, diélectriques et d’ancrage des phases N et NTB des mélanges. Les propriétés optiques sont très différentes de celles du CB7CB sur une large gamme de composition et de forts effets pré-transitionnels sont observables à l'approche de ϕ_c≈20%. Les propriétés d’ancrage (fig1) sont également significativement modifiées par l'ajout de 8CB au CB7CB ce qui facilite l'alignement homéotrope, très difficilement obtenu pour le CB7CB.

Heliconal nematic twist bend (NTB) phases are frequently found at high temperatures. In the last years the search of stable room-temperatures NTB phases has led to the synthesis of new compounds [1] and to the design of multicomponent systems. Mixtures of NTB compounds with nematogens ,such as 4-Cyano-4'-pentylbiphenyl (5CB) dimeric liquid crystal 1,7-bis(4-cyanobiphenyl-4-yl) heptane (CB7CB) decrease strongly the temperature range of the NTB phase and tune the optical, thermal and dielectric properties of NTB [2]. In this work we have explored the physical properties of mixtures of CB7CB with several smectogens with a particular focus on 4′-octyl-4-biphenylcarbonitrile (8CB). The 8CB/CB7CB phase diagram reveals striking features compared to the 5CB/CB7CB one. Despite their macroscopic resemblance, SmA and NTB domains appear incompatible and remain separated by a nematic phase that extends to very low temperature (-20°C) at a CB7CB fraction of ϕ_c≈20%. We have characterized the optical, thermal, dielectric and anchoring properties of the N and NTB phases of the mixtures. Compared to the pure CB7CB system, the N phase shows unusual behavior over a large range of composition and reveals strong pre-transitional effects when approaching ϕ_c. We also found that, for specific aligning substrates, adding 8CB to CB7CB drastically changes the anchoring properties (fig1) facilitating homeotropic alignment. [1] Yuan Wang, Quan Li; Room temperature heliconical twist-bend nematic liquid crystal; Cryst. Eng. Comm; 17; 2778-2782; 2015. [2] Nina Trbojevic and Mamatha Nagaraj; Dielectric properties of liquid crystalline dimer mixtures exhibiting the nematic and twist-bend nematic phases; Phys. Rev. E ;96; 052703; 2017.

International audience; Natural protein sources often display a huge complexity, being composed of a blend of polypeptides of various molecular weight, pHi and charge density. Gluten, the proteins extracted from wheat flour is one of such. Gluten is widely used for its viscoelastic properties as an improver of cereal products (bread, pastry, etc.). It is composed of two classes of proteins, named gliadin and glutenin, similar in their amounts in glutamine (30%) and proline (10%). The more than 25 different polypeptides belonging to the gliadin class are hard to fractionate into individual components because of high redundancy in the primary sequences. Glutenin are in the form of polymers made from several distinct polypeptides concatenated through inter-chain disulfide bonds. Their molecular weights are evenly distributed from 100 kg/mol to 7,000 kg/mol.While it is well established that gliadin confers viscosity to gluten whereas glutenin polymers are at the origin of its elastic resistance, the interactions existing between both classes of gluten protein remain unknown. We previously showed by SLS and multi-angle DLS that gluten proteins suspended in ethanol/water (50/50, v/v), a theta solvent, includes large proteins assemblies (26,000 kg/mol, Rh 100nm) displaying an internal dynamic1. To get a better insight of the composition of those assemblies, we combined biochemical and physicochemical approaches. On the one hand, gluten proteins suspended in ethanol/water were fractionated by Asymmetrical- Flow-Field-Flow Fractionation (A4F) coupled to UV, SLS and QELS detectors. On the other hand, gluten proteins were partitioned by liquid-phase decomposition in respect with temperature. Protein composition of partitioned phases and eluting fractions recovered from A4F were characterized by size-exclusion chromatography. A specific interaction between omega-gliadin and glutenin polymers was evidenced.This result strengthens a very recent study that demonstrates a significant positive correlation between glutenin polymeric proteins, the ω‐gliadin fraction, and dough properties.

International audience; Despite the relevance to environmental, biological and industrial processes, the motion of a colloidal particle close to a fluid interface and the way it interacts with the water surface are still largely elusive and intriguing physical phenomena.We explored the system of individual colloidal particles close to an air-water interface by recording highly resolved 3D trajectories through a dual wave reflection interference setup (DW-RIM). Contrary to other established experimental techniques, DW-RIM allows accurate measurements of the absolute particle-interface distance and thus does not require any calibration or assumption to know the location of the interface. The particle-interface system shows two different potential energy landscapes resulting to two different equilibrium particle-interface distances. The larger one can be fairly explained by Van der Waals and electrostatic interactions combined with gravity. The shorter one highlights the existence of an unexpected additional attractive interaction. Surface heterogeneities as possible origin of such an interaction are considered and discussed.Concerning the friction the particle undergoes, the air-water interface peculiarly acts as a slip boundary for the particle motion parallel to the interface and as a no-slip boundary for the perpendicular motion. This experimental result is rationalized considering recent models based on surface incompressibility.

International audience; Hydrogen is considered to be the preferred successor to gasoline due to its clean combustion.However, efficient and save storage of hydrogen remains the bottle-neck and one of the main challenges in hydrogen-basedtechnologies. In the past we have justified [1] the necessary conditions (materials physical properties) the hydrogenadsorbents MUST simultaneously fulfilled to be used in mobile applications: it must exhibit the specific surface at least ofthe order of 5000–7000 m2/g, have the average binding energy above 10 kJ/mol, and the density above 0.6 kg/m3. This setof parameters put so strict constrains on possible solutions that such systems are neither yet known nor seem easy tosynthesize.Here we explored the possibility to prepare boron-substituted nanoporous carbons, cheap, light and save material that wassupposed [2,3] to reversibly store hydrogen by physisorption at room temperatures and moderated pressure (< 120 bar). Weshowed that electric arc discharge between graphite electrodes may be optimized to produce graphitized structures with avariety of graphene fragment sizes, forms, and interconnections between them. It also allows to introduce boron heteroatominto graphite-like structure. The as-synthetized material shows the hydrogen binding energy twice as high as unsubstitutedcarbons, but requires post-treatment (activation) as the its surface is low (~200 m2/g).

Low frequency lattice vibrations (phonons) can be used as indicators of a variety of structural transformations. In particular, conformational changes in flexible metal-organic frameworks (MOFs) can be successfully explained by analyzing materials phonon spectrum in frequency range below 200 cm-1 [1,2]. It has been shown that such lattice vibrations are responsible for pressure- and adsorption-induced gate-opening in zeolitic imidazolate frameworks (ZIFs), and pore breathing in materials from MIL-53 family. In this work we present a phonon-based methodology to analyze MOFs deformations that can be detected in adsorption experiments but cannot be explained at the microscopic level without theoretical support based on numerical simulations.As a case study we have chosen to analyze adsorption-induced transformations in ZIF-8. The step-like adsorption isotherm observed in this material was interpreted in the literature as a signature of gate-opening (enlargement of the pore free volume) induced by the increasing number of guest molecules entering the pore. To analyze this phenomenon at the microscopic level, we first calculated and visualized normal modes of the lattice vibrations. For that, density functional theory (DFT) with PBE functional and empirical dispersion correction D3(BJ) was used. Only the modes which fulfill two criteria: (i) their frequency is below 200 cm-1, and (ii) the related lattice deformation leads to increase of the pore free volume, have been further analyzed. These deformed structures, (including one related to gate-opening, pore breathing and one which combines both deformations) were selected to serve as the adsorbent model. Grand Canonical Monte Carlo (GCMC) simulations have been performed to calculate the isotherms of adsorption in selected structures. Surprisingly, in the structure related to gate-opening, the mode, located at ~40 cm-1, and considered in the literature as the one responsible for step-like form of the isotherm did not provided an uptake larger than the undistorted structure. On the other hand, in the structure resulting from simultaneous pore breathing and gate-opening deformation the adsorption is significantly increased. Therefore, we consider that this deformation, induced by pore breathing and gate-opening phonons explains better the experimental observations..1. F. Formalik, et al., Microporous and Mesoporous Materials, (2018),2. M. R. Ryder, et al., Physical Review Letters, 113 (2014), 215502-21550

International audience; A classical computer with N bits (transistors), has $2^N$ possible states, and the computation process consists in switching on or off certain transistors according to a prescribed program. In contrast, the quantum computer with N qubits (spins) is characterized by $2^N$ quantum amplitudes, which are continuous complex variables. Thus, a toy quantum computer with, say, 50 qubits will be characterized at any given moment by $2^{50} = 1125899906842624$ continuous parameters, which we should be able to manipulate at will. However the number of qubits needed to have a useful machine (i.e. one that can compete with your laptop in factoring very large numbers) is estimated to be $10^3$−$10^5$. The number of continuous variables describing the state of such an apparatus at any given moment is at least $2^{1000}$ (~$10^{300}$) which is much, much greater than the number of particles in the entire Universe (only ~$10^{80}$)! Thus the answer to the question in the title is: As soon as the physicists and engineers will learn to control this quantity of continuous parameters!In recent years the trend is to advertise as quantum computers circuits made from truly quantum devices based on Josephson junctions at liquid helium temperatures, an approach that was initially started by the D-wave company, followed and developed by IBM, Google, Microsoft, and others. This is not going to be the quantum computer everyone was talking about during the last 20 years, as it will not be able to factor large numbers by Shor's algorithm. It will not and cannot compute anything at all, except its own ground state, a process labeled as "quantum annealing". After initial preparation, any system, whether classical or quantum, at low temperature will relax to its ground state. Calculating the ground state of a more or less complex quantum system, either analytically or numerically, is usually impossible – this is what originally inspired Feynman's idea of quantum computing. However, we can measure some properties of this ground state. (The full characterization of the ground state requires measuring $2^N$ parameters).It is not entirely clear what will be the possible practical use of such systems. However, such modeling might provide some additional knowledge on the behavior of large and complicated quantum systems.

In vitro, depending on extracellular matrix (ECM) architecture, macrophages migrate either in amoeboid or mesenchymal mode; while the first is a general trait of leukocytes, the latter is associated with tissue remodelling via Matrix Metalloproteinases (MMPs). To assess whether these stereotyped migrations could be also observed in a physiological context, we used the zebrafish embryo and monitored macrophage morphology, behaviour and capacity to mobilisation haematopoietic stem/progenitor cells (HSPCs), as a final functional readout. Morphometric analysis identified 4 different cell shapes. Live imaging revealed that macrophages successively adopt all four shapes as they migrate through ECM. Treatment with inhibitors of MMPs or Rac GTPase to abolish mesenchymal migration, suppresses both ECM degradation and HSPC mobilisation while differently affecting macrophage behaviour. This study depicts real time macrophage behaviour in a physiological context and reveals extreme reactivity of these cells constantly adapting and switching migratory shapes to achieve HSPCs proper mobilisation.

International audience; Challenges of public health and sustainable development require replacing in food products animal proteins by plant proteins. In this optics, it is crucial to understand the structure and kinetic of formation of a film of plant proteins in order to improve the control of emulsions and foams stabilized by these proteins.In this talk we will present experimental results on the behaviour interfacial properties of wheat gluten, sunflower and rapeseed proteins at liquid interfaces. Thanks to a combination of tensiometry, dilatational rheology and ellipsometry, rational physical pictures of the dynamics of the interfacial properties are achieved, for the various proteins and at both air/water and oil/water interfaces. For gluten proteins, a time-concentration superposition of the data is evidenced whatever the subphase concentration, which reveals that the kinetics of protein adsorption at the interface is dominated by bulk diffusion. We propose a consistent physical picture of the multistep diffusion-controlled irreversible adsorption of the gliadin proteins at an air/water interface, and evidence surface-induced conformational changes of the proteins followed by film gelation [1]. Sunflower and rapeseed proteins by contrast do not reorganize once adsorbed at an interface and display a simpler dynamics of film formation. In addition the failure at high concentration of the time-concentration superposition of the tensiometry and viscoelastic data strongly suggest a surface-induced aggregation process, which we confirm with turbidity measurements. By quantitatively comparing the surface pressure dependence viscoelasticity of the various interfaces, we hightlight the crucial role on the behavior of plant proteins at liquid interfaces of the solvent quality and of the protein softness, that is discussed in regard to the protein structure.

International audience; Heliconal nematic twist bend (NTB) phases are usually not well oriented in planar commercial cells, even in thin (~1 µm) ones where a micron-sized periodic texture is usually observed [1,2,3] (see Fig.1-a). The origin of the stripe patterns is attributed to the rapid shrinking of the pseudo-layers below the N-NTB phase transition temperature, which yields an undulation instability. The observed periodicity is found to be twice the cell gap [1].We have explored the effect of the strength of the anchorings of the substrates on the resulting patterns. We used polymer aligning layers of tunable azimuthal and zenithal strengths to design liquid crystal cells with surface anchorings ranging from ultraweak to strong. We then have studied the patterns formed by the NTB phase of 1,7-bis-4-(4-cyanobiphenyl) heptane (CB7CB). We will show how the period of the stripes can be varied in a large range in cells of the same thickness but with different anchoring preparations. With adequate anchoring conditions (see Fig.1-b-c), an excellent and spontaneous planar alignment of the NTB phase of CB7CB can be obtained much below the phase transition temperature.References: [1] Panov V.P. et al, Phys. Rev. Lett., 2010, 105; 167801.[2] Challa P. K. et al, Phys. Rev. E: Stat., Nonlinear, Soft Matter Phys., 2014, 89, 060501.[3] Vaupotič N. et al., Chem. Phys. Chem., 2018, 19,2566.

International audience; Storage and separation of gases is one of the most challenging processes when they have to be implemented at industrial scale. Hundreds of potential materials have been tested over the past years, especially for gas storage (hydrogen and methane for fueling applications) and separation of biogas (a mixture of 55 – 75% of methane 25 – 45% of carbon dioxide). Today, MOFs (Metal-Organic Frameworks) [1-2] are considered as the most promising materials for such applications. MOFs are hybrid, nanoporous materials with a very large surface area, in which pore sizes, shapes and adsorption energies can be almost unlimitedly tailored to fit the required adsorption characteristics. A particular category of these materials are the so-called breathing MOFs, in which a reversible structural transformation (variation of pore volume, pore breathing) can be induced by temperature, pressure or interaction with adsorbate molecules. Molecular modeling is an effective way to rapidly obtain microscopic information on the mechanism of adsorption in these materials (in many cases, not accessible using traditional experimental methods) and to shorten the time necessary to implement research results in an industrial process.In the this work we will present simulations of methane and carbon dioxide adsorption in a wide range of MOF structures from CoRE-MOF database [3], and at variable content of humidity. MOFs with pore limiting diffusion (PLD) over 3.3 Å were chosen for the simulations. Due to the humid conditions we chose structures from the middle range of hydrophilicity, kH between 5·10-2 mol/kg·Pa (CuBTC) and 5·10-6 mol/kg·Pa (ZIF-8). Over 1000 structures have been tested using Grand Canonical Monte Carlo method (as implemented in RASPA code) to find the optimal material for the CH4/CO2 separation in conditions of increasing humidity. The initial screening allowed us to select the most promising structures for more detailed investigation. We show that 16 materials exhibit very promising selectivity (defined as adsorbed amount of CO2¬ to amount of CH4) in range from 50 to 440. Furthermore, adsorption of methane tends to be reduced with increasing humidity. Reference[1]S. Li, Y. G. Chung, and R. Q. Snurr, “High-Throughput Screening of Metal–Organic Frameworks for CO 2 Capture in the Presence of Water,” Langmuir, vol. 32, no. 40, pp. 10368–10376, 2016.[2]R. Krishna, “Screening metal–organic frameworks for mixture separations in fixed-bed adsorbers using a combined selectivity/capacity metric,” RSC Adv., vol. 7, no. 57, pp. 35724–35737, 2017.[3]Y. G. Chung et al., “Computation-Ready, Experimental Metal–Organic Frameworks: A Tool To Enable High-Throughput Screening of Nanoporous Crystals,” Chem. Mater., vol. 26, no. 21, pp. 6185–6192, Nov. 2014.

Unlike macroscopic objects, any system of nanometric size shows characteristics that strongly depend on its size and geometric form.Here we focus on the influence of confinement on properties of fluids, when the confining volumes are of nanometric size.Using Grand Canonical Monte Carlo simulations we show that when a fluid is confined in nano-volume, delimited by non-attracting pore walls,its density is heterogeneous close to the pore wall, and, on average over the whole pore volume, it is smaller than the density of bulk fluid. Thisfluid heterogeneity, resulting from the nano-confinement, progressively weakens when the pore size increases, and totally disappears inside thepores larger than 5 nm. On the other side, in the limit of very small pores, the fluid density approaches the ideal gas value. This effect should bedistinguished from the well know heterogeneity of density of fluids adsorbed in nanopores, driven by the difference between the strength offluid-fluid and fluid-pore wall interactions, that varies with the distance from the pore wall.We show that the density distribution inside the non-attracting reservoir strongly depends the distance from the pore walls, and the pore size andshape. Such a behavior, although non-intuitive in macroscopic sample, has a simple physical explanation. The energy of a given gas moleculestrongly depends on the number of its nearest neighbors. In the nanopores this number decreases when the molecule is closer to the pore wall.Less intuitive is the observation that at higher pressures (p > 100 bar) the density of the gas close to the wall may be higher than in the middle ofthe pore, and even higher than the one of the bulk gas at the same thermodynamic conditions.

International audience; Heliconal nematic twist bend (NTB) phases are usually not well oriented in planar commercial cells, even in thin (~1 µm) ones where a micron-sized periodic texture is usually observed [1,2,3] (see Fig.1-a). The origin of the stripe patterns is attributed to the rapid shrinking of the pseudo-layers below the N-NTB phase transition temperature, which yields an undulation instability. The observed periodicity is found to be twice the cell gap [1].We have explored the effect of the strength of the anchorings of the substrates on the resulting patterns. We used polymer aligning layers of tunable azimuthal and zenithal strengths to design liquid crystal cells with surface anchorings ranging from ultraweak to strong. We then have studied the patterns formed by the NTB phase of 1,7-bis-4-(4-cyanobiphenyl) heptane (CB7CB). We will show how the period of the stripes can be varied in a large range in cells of the same thickness but with different anchoring preparations. With adequate anchoring conditions (see Fig.1-b-c), an excellent and spontaneous planar alignment of the NTB phase of CB7CB can be obtained much below the phase transition temperature. [1] Panov V.P. et al; Spontaneous Periodic Deformations in Nonchiral Planar-Aligned Bimesogenswith a Nematic-Nematic Transition and a Negative Elastic Constant; Phys. Rev. Lett. ; 105; 167801; 2010.[2] Challa P. K. et al; Twist-bend nematic liquid crystals in high magnetic fields; Phys. Rev. E: Stat., Nonlinear, Soft Matter Phys.; 89; 060501; 2014.[3] Vaupotič N. et al.; Polarization Gratings Spontaneously Formed from a Helical Twist‐Bend Nematic Phase; Chem. Phys. Chem.; 19; 2566; 2018.

International audience; Here we explored the possibility to prepare boron-substituted nanoporous carbons, cheap, light and save material that wassupposed [2,3] to reversibly store hydrogen by physisorption at room temperatures and moderated pressure (< 120 bar). Weshowed that electric arc discharge between graphite electrodes may be optimized to produce graphitized structures with avariety of graphene fragment sizes, forms, and interconnections between them. It also allows to introduce boron heteroatominto graphite-like structure. The as-synthetized material shows the hydrogen binding energy twice as high as unsubstitutedcarbons, but requires post-treatment (activation) as the its surface is low (~200 m2/g).

International audience; We discuss the mechanism of the structural transformations of gas adsorbed in microporous crystalline solids. We show that it is possible to induce structural transformations in a confined system by simply varying the number of molecules adsorbed in the pore. We found that the mechanism of these novel, adsorption-induced structural transformation in nano-pores differs from the capillary condensation. First, the structure of the confined gas is determined by a competition between adsorption sites attractive forces and intermolecular interaction. Second, at low temperature, the transformation is discontinuous because it is defined by limited number of accessible adsorption sites [1,2]. In the case of methane adsorbed in IRMOFs porous structures the character of transformation depends on temperature but also on the IRMOF structure: it changes from strongly discontinuous (especially at low temperatures), to continuous transition. The mechanism of the transformation is also modified by the size of the gas molecules and the strength of interaction. However, even discontinuous transition can produce continuous isotherms. We will show that the continuous isotherm can be the effect of statistical dynamical switching between two phase, characterized by different number of adsorbed molecules. We show the simulated microscopic mechanism and experimental observations support such statistical interpretation. This work was supported by the Polish National Science Centre (NCN, grant no. 2015/17/B/ST8/00099). The calculations have been partially performed at the WCSS computer center of The Wroclaw University of Science and Technology, grant no 33.References[1] Heterogeneous melting of methane confined in nano-pores. Dundar, E.; Boulet, P.; Wexler, C.; et al. J. Chem. Phys. 145, 144704 (2016)[2] Adsorption-Induced Structural Phase Transformation in Nanopores. Kuchta, Bogdan; Dundar, Ege; Formalik, Filip; et al. Angewandte Chimie In. Ed. 56, 16243–16246. (2017)

International audience; ...

International audience; Excitons in wide nitride Quantum Wells (QWs) are naturally indirect due to the strong internal electric field: within such excitons the electron and the hole are spatially separated, resulting in strong dipole moments and long radiative lifetimes. These properties offer the possibility to explore the collective exitonic phases with complex phase diagrams predicted theoretically in the temperature-density-dipole moment parameter space. Here we study 8 nm-wide GaN/(AlGa)N QWs presenting 1MV/cm built-in electric field in the growth direction, microsecond-long radiative lifetimes, 8 meV exciton emission linewidth and 100 µm transport lengths at cryogenic temperatures. To address the quasi-equilibrium properties of the strongly dipolar excitons (i.e. whose electric dipoles are twice as long as their Bohr radii d = 2aB), we confine them in the QW’s plane using electrostatic traps with a semi-transparent Schottly electrode. These traps consist in semitransparent electrodes deposited on the sample’s surface. We make micro-photoluminescence (µPL) measurements (less than 1µm- resolution) upon point-like optical excitation. We thus obtain the spectrally resolved information on the emission of the excitons as a function of power and density. Our experiments demonstrate an efficient trapping of excitons in the plane of the QW, with a trapping potential of an order of 50 meV. We demonstrate that it is possible to uniformly fill areas up to hundreds of microns in length with excitons and/or electron hole pairs in the QW’s plane. At T=4K, the emission from these areas exhibits a peculiar behavior. At low densities, such that there is no measurable screening of the built-in electric field, the emission from the trap is weak and spatially homogeneous. However, for weak built-in electric field screenings (as low as 10 meV, ~1011 cm-2 pair density), the PL brightens up and becomes spatially inhomogeneous – droplet like. We tentatively interpret this fragmentation as the coexistence of the gas and liquid phases of the excitons. As expected, the fragmented character of the emission disappears when either power and/or temperature is further increased, due to either exciton heating (gas phase), ionization or dissociation (Mott transition). Our results suggest that excitons in GaN QWs are promising candidates for the study of collective phenomena in cold dipolar bosonic systems. The advantages of the nitrides over arsenides include both higher critical temperatures for the onset of collective phenomena, and the ability to increase the dipolarity of systems based on their small exciton Bohr radius.

International audience; Double-walled carbon nanotubes (DWNTs), consisting of two coaxial and weakly van der Waals coupled single-walled carbon nanotubes (SWNTs), are one of the most ideal and fundamental systems to study the effects of inter-tube coupling on the physical properties in one-dimensional structures.On this poster, we report on the investigations of individual, spatially isolated and suspended double-walled carbon nanotubes (DWNTs) by combination of high-resolution electron microscopy, electron diffraction, Rayleigh spectroscopy and Raman spectroscopy (Figure 1) [1,2]. We first present an overview of the effect of the diameters, inter-tube distance and nature (metallic or semiconducting) on the Raman signature (Radial Breathing Like [1,3,4] and Tangential Modes [4-6]) of DWNTs. We then examine the features of tangential modes and find a clear frequency shift of the inner-layer G modes as a function of the inter-tube distance with respect to the corresponding G modes in equivalent single-walled carbon nanotubes (SWNT).[4-6] These results are understood by considering the effects of the relaxation of the layers and the interaction between the relaxed structures.[7] Finally, we study the experimental excitation dependence of the G modes intensity of the constituent inner and outer SWNTs. In particular, we discuss the effects of the quantum interference between different electronic transitions on the observed behaviors.[8]References[1] D.I. Levshov et al., Carbon, 114, 141 (2017). [2] D.I. Levshov et al., Phys Rev. B 96 (2017), 195410.[3] D.I. Levshov et al., Nano Lett. 11(11) (2011), 4800. [4] H.-N. Tran et al., Adv. Nat. Sci. Nanosci. Nanotechnol. (2017), 8, 15018.[5] D. Levshov et al., J. Phys. Chem. C 119(40) (2015), 23196.[6] D.I. Levshov et al., Phys. Status Solidi B 254(11) (2017), 1700251.[7] V.N. Popov et al., Phys. Rev. B 97 (2018), 165417.[8] H.-N. Tran et al., Phys. Rev. B 95 (2017), 95 (20), 205411

International audience; Maszyny molekularne [1], zwane także nano-maszynami, są obiektami w skali nanometrycznej, które mogą wykonywać ruchy translacyjne i/lub rotacyjne charakterystyczne dla urządzenie mechanicznych. Synteza tego typu nano-obiektów, to jest nowa rozwijająca się dziedzina, której znaczenie zostało potwierdzone przez przyznanie nagrody Nobla w dziedzinie chemii w 2016 roku [2-4]. W niniejszej prezentacji dyskutujemy rozwój tej dziedziny od czasów Richard’a Feynmann’a [5] do czasów współczesnych, z akcentem na aktualny ‘state of art’ w tej działalności.Przedstawimy koncepcję molekularnego motoru [6] i przedyskutujemy rożne aspekty związane z jego funkcjonowaniem: źródła energii, wpływ masy i lepkości otoczenia, oraz rolę ruchów Browna, a tym samym zwrócimy uwagę na termodynamiczne nierównowagowe aspektu nano-systemów.

International audience; W odróżnieniu od obiektów makroskopowych, własności układów o rozmiarach nanometrycznych silnie zależą od ich wielkości i kształtu. Wynika to z faktu, iż większość atomów nanoobiektów znajduje się na ich powierzchni, i ich ich energia kohezji jest mniejsza niż atomów wewnątrz układu. Pokażemy, że gęstość gazu zamkniętego w objętości (w porze) o rozmiarach nanometrycznych, ograniczonej nieoddziaływującymi ścianami jest niejednorodna, i mniejsza (średnio) niż gęstość gazu w skali makroskopowej. Niejednorodność rozkładu gęstości maleje gdy rozmiary układu rosną, i jest zaniedbywalna dla obiektów o rozmiarach powyżej 5 nm. Z drugiej strony, gdy rozmiary poru maleją, gęstość gazu zbliża się do wartości gęstości gazu doskonałego. Efet ten należy odróżnić od niejednorodności gęstoci gazów zaadsorbowanych w nanoporach, spowodowanej różnicą siły oddziaływania gaz-gaz i gaz-adsorbent, która zmienia się wraz z odległością od adsorbenta. Wynik ten ma fundamentalne znaczenie w opisie ilościowym zjawisk adsorpcji, i poprawnym oszacowaniu adsorpcji całkowitej i nadmiarowej w nanoporach. Obie wielkości są obliczane zakładając stałą i jednorodną gęstość gazu w danych warunkach termodynamicznych (p,T), wyznaczoną dla obiektów makroskopowych. Ponadto objętość zajmowana przez gaz w nanoporach nie jest prosta i jednoznaczna do zdefiniowania. Tymczasem obie wielkości: objętość poru i gęstość gazu jaki można pomieścić (bez adsorbcji) w nanoporze są wielkościami niezbędnymi dla poprawnej ilościowej interpretacji eksperymentalnych izoterm adsorbcji. Przeanalizujemy ten aspekt na przykładzie sześciu gazów : badanych intensywnie nośników energii H2 i CH4, używanych do charakteryzacji materiałów porowatych N2, Ar i Kr, oraz CO2, podstawowego gazu cieplarnianego. Praca wykonana w ramach grantu French National Research Agency ANR, grant HYSTOR no. ANR-14-CE05-0009.

International audience; At the nanoscale the positions of coexistence lines on the phase diagrams are shifted and their new locations depend mainly on the size and shape of the nano-confinement, the structure of the confining walls, and their interaction with the confined substance. Here we show that it is possible to induce structural transformations in a confined system by simply varying the number of molecules adsorbed in the pore. We found that the mechanism of these novel, adsorption-induced structural transformation in nano-pores differs from the capillary condensation. First, the structure of the confined gas is determined by a competition between adsorption sites attractive forces and intermolecular interaction. Second, at low temperature, the transformation is discontinuous because it is defined by limited number of adsorption sites [1,2]. The confined, equilibrium structures are not characterized by mean positions of molecules but rather by a probability distribution of molecular positions around adsorption centres. This distribution changes when the number of molecules in the pore increases. The character of transformation is temperature dependent: strongly discontinuous at low temperature, it evolves into a continuous transition when the temperature increases. The mechanism of the transformation is also modified when the size of the gas molecules and types of interaction change. In particular, we report the existence of the intermediate phase, observed only above a critical strength of the attractive interactions. This work was supported by the Polish National Science Centre (NCN, grant no. 2015/17/B/ST8/00099). The calculations have been partially performed at the WCSS computer center of The Wroclaw University of Science and Technology, grant no 33.

International audience; Microlasers covering the UV to blue spectral range are important building blocks for biochemical detection applications. This work presents a series of microdisk lasers realized within the same GaN-on-Si photonic platform scheme, and operating at room temperature under pulsed optical pumping over a broad spectral range extending from 275 nm to 470 nm. The III-nitride microdisks embed either binary GaN/AlN multiple quantum wells (MQWs) for UV operation, or ternary InGaN/GaN MQWs for violet and blue operation. The fabrication process is based on e-beam lithography and the release of the nitride membrane after selective under-etching of the silicon susbtrate, and has led to high quality factor resonators, microdisks as well as photonic crystal cavities, within the same platform. A detailed comparison of these microlasers leads to the conclusion that for our Q>1000 microdisk resonators, the pumping threshold is determined by the type of optical excitation, resonant with the barrier or with the MQW excited states, and the emission efficiency of the MQWs [Sellés et al., APL 109, 231101 (2016) and Sci. Rep. 6, 21650 (2016)].

International audience; Aqueous dispersions of graphene-derived monolayers form liquid crystal at rather low concentrations due to the high aspect ratio of these flakes [1,2]. If graphene oxide dispersions are easily obtained in water, reduced graphene oxide necessitates the use of surfactants [3]. Preparing organized materials and thin films from these dispersions then requires a good control of the liquid crystal ordering during the deposition and the drying of the films.The flakes easily align at high shear [4,5], which has allowed us to complete previous optical characterizations of the various graphene layers (birefringence and linear dichroism). However at low shear or under small dispalcements, thin films often show peculiar patterns (such as the periodic textures shown in Fig.1). We have shown how to create and stabilize large-sized periodic textures. The patterns have been characterized under optical and electronic microscopies. Their stability can be explained by the competition between the anchoring field of the substrate and the presence of a yield stress resulting from the peculiar elastic and rheological properties of the graphene oxide liquid crystals. Our results also clarify why long-standing hypotheses on the presence of exotic phases [1] at large concentrations are present in the literature.References[1] Z. Xu, C. Gao Nat Commun., 2, 571 (2011).[2] C. Zakri et al., Phil. Trans. A, 371, 20120499 (2013).[3] C. Zamora et al, J. Phys. Chem. Lett. 3, 2425 (2012).[4] P. Poulin et al, Proc Natl Acad Sci USA, 113, 11088 (2016).[5] S-H Honga, T.Z. Shena and J. K. Songa, Liquid Crystals, 42, 261 (2015)

We discuss the intrinsic optical spectroscopy (UV-vis-NIR absorption, Raman and photoluminescence)signatures of single layer graphene (SLG) and single wall carbon nanotubes (SWNT) dispersed indegassed water without additives, so called "eau de graphene" (EdN) [1-3] and ‘‘eau de nanotubes”(EdN) [4].The most characteristic signature of SLG in EdG is a narrow and symmetric 2D band with a widthdepending on processing conditions [2,3]. The position of the G and 2D bands indicate moderate biaxialcompressive strain and weak n doping. The intensity of the D band and the width of the G band arediscussed in terms of point-defect density and flake size. We show that point defects can be easily curedby preparing thin films from EdG and annealing at 800°C.The signatures of SWNT in EdN are found to be very close to those of SWNT dispersed in aqueoussuspensions stabilized with surfactants [4]. Absorption peaks appear to be even slightly better resolvedfor EdN, suggesting sharper excitonic resonances, which is also supported by the Raman data. Thesesignatures support that SWNT are dispersed as individuals in EdN, in a similar way SLG aredispersable in EdG [1-3].[1] G. Bepete et al, Nat. Chem. 2016, DOI 10.1038/NCHEM2669[2] G. Bepete et al, J. Phys. Chem. C 2016, 120 (49), 28204–28214.[3] G. Bepte et al, Phys. Stat. Solidi 2016, 10 (12), 895-899.[4] G. Bepete et al, to be published

International audience; Gliadins are edible wheat storage proteins well known for their surface active properties. In this paper, we present experimental results on the interfacial properties of acidic solutions of gliadin studied over 5 decades of concentrations, from 0.001 to 110 g/L. Dynamic pendant drop tensiometry reveals that the surface pressure  of gliadin solutions builds up in a multistep process. The series of curves of the time evolution of collected at different bulk protein concentrations C can be merged onto a single master curve when  is plotted as a function of t where t is the time elapsed since the formation of the air/water interface and  is a shift parameter that varies with C as a power law with an exponent 2. The existence of such time-concentration superposition, which we evidence for the first time, indicates that the same mechanisms govern the surface tension evolution at all concentrations and are accelerated by an increase of the bulk concentration. The scaling of  with C is consistent with a kinetic of adsorption controlled by the diffusion of the proteins in the bulk. Moreover, we show that the proteins adsorption at the air/water interface is kinetically irreversible. Correlated evolutions of the optical and elastic properties of the interfaces, as probed by ellipsometry and surface dilatational rheology respectively, provide a consistent physical picture of the building up of the protein interfacial layer. A progressive coverage of the interface by the proteins occurs at low . This stage is followed, at higher , by conformational rearrangements of the protein film, which are identified by a strong increase of the dissipative viscoelastic properties of the film concomitantly with a peculiar evolution of its optical profile that we have rationalized. In the last stage, at even higher surface pressure, the adsorption is arrested; the optical profile is not modified while the elasticity of the interfacial layer dramatically increases with the surface pressure, presumably due to the film ageing.

International audience; Double hydrophilic block copolymers (DHBC) in the presence of multivalent oppositely charged ions form polyion complexes (PIC) in the micellar form. We use PIC micelles as an ecofriendly structuring agents for templating ordered mesoporous materials [1,2] : after concomittant micellization and silica condensation, the porosity of the final material is revealed by simple elution in water and the polyions can be recycled in successive synthesis batches. Various mesoporous silica materials have been obtained from cubic to lamellar, although lyotropic behavior of PIC micelles on their own has seldom been reported if ever. Moreover, the control over the structure of the final material is not solely determined by the asymmetry ratio of the diblock copolymer : a single PIC system yields different mesostructured silica materials depending on the physico-chemical conditions. In an attempt to address the relation between the mesoporous material structure and the lyotropic behavior of these new templating agents, our attention was brought to the role of water which is actually a prominent constituent of PIC micelles.PIC micelles of PEO-b-PAA/oligoamines have been studied. The water content of the core of the micelles has been addressed by establishing the complete phase diagram of the polyelectrolyte complex PAA/oligoamine in its coacervate form. It amounts to 50%, varies non-monotonously with concentration and can be tuned by ionic strength, pH. Shape transition and phase transition are revealed by swelling laws of the correlation peak position obtained from X-ray scattering. From light scattering and osmometry we establish the equation of state  of a PEO-b-PAA/oligoamine electrostatic complex. Its lyotropic behavior is characterized by a transition of shape of the micelles at =0.16 and a transition to lamellar phase at =0.30 corresponding to various levels of deswelling of the corona and of the core.This study evidences the high compressibility of the core of the micelles as opposed to the core of amphiphilic copolymer micelles. This feature probably explains why lyotropic behavior of PIC micelles is less rich than the one of amphiphilic micelles. But it also brings versatility in the use of PIC micelles as templating agents for mesoporous materials.

International audience; Unlike macroscopic objects, any system of nanometric size shows characteristics that strongly depend on its size and geometric form. It is the consequence of the fact that the major part of atoms (or molecules) of nano-object is located at its surface, their cohesive energy is smaller than for the atoms in the bulk. Here we show that when a fluid is confined in nano-volume, delimited by non-interacting pore walls, its density is heterogeneous, decreases close to the pore wall, and, on average, is smaller than the density of bulk fluid. The heterogeneity of distribution of fluid density, resulting from the nano-confinement, progressively weakens when the pore size increases, and totally disappears for pores larger than 5 nm. On the other side, in the limit of very small pores, the fluid density approaches the ideal gas value. This effect should be distinguished from the well know heterogeneity of density of fluids adsorbed in nanopores, driven by the difference between the strength of fluid-fluid and fluid-pore wall interactions, that varies with the distance from the pore wall. The reported observation has non-trivial influence on evaluation of excess/total adsorption in nanopores, as these two quantities are calculated assuming the known – and homogeneous – bulk density of gas in the pore. Additionally, the gas density in the pores depends on the definition of the pore volume which is neither straightforward nor unique. The right estimation of both: pore volume and gas density is essential for quantitative interpretation of experimental adsorption isotherms: evaluation of pore size distribution and of the amount of adsorbed gas. We analyze this problem on an example of five gases: H2, CH4, the two intensively studied energy vectors, and N2, Ar, and Kr, commonly used for characterization of porous structures. For H2, the distributions of densities of gas confined in adsorbing and not adsorbing pores are compared and commented.

International audience; At the nanoscale the positions of coexistence lines on the phase diagrams are shifted and their new locations depend mainly on the size and shape of the nano-confinement, the structure of the confining walls, and their interaction with the confined substance. Here we show that it is possible to induce structural transformations in a confined system by simply varying the number of molecules adsorbed in the pore. We found that the mechanism of these novel, adsorption-induced structural transformation in nano-pores differs from the capillary condensation. First, the structure of the confined gas is determined by a competition between adsorption sites attractive forces and intermolecular interaction. Second, at low temperature, the transformation is discontinuous because it is defined by limited number of adsorption sites1,2.The confined, equilibrium structures are not characterized by mean positions of molecules but rather by a probability distribution of molecular positions around adsorption centres. This distribution transforms when the number of molecules in the pore increases. The character of transformation depends on temperature: it is strongly discontinuous at low temperature but evolves into a continuous transition when the temperature increases. Here we show how the mechanism of the transformation is modified by temperature and also by different types of interaction and the size of the gas molecules. In particular, the existence of the intermediate phase is observed only above a critical strength of the attractive interactions.

International audience; How the Neveu-Schwarz string was discovered is the result of a most unlikely sequence of four coincidences.

International audience; It is well know that the properties of nano-objects differ from those of their macroscopic analogs. Any system of nanometric size shows characteristics that strongly depend on its size and geometric form. It is mainly because the major part of atoms (or molecules) of nano-volume are located at the object surface and their cohesive energy is smaller than for the atoms in the bulk. As a consequence, the density of the nanoobjects is not homogeneous, and may decrease close to the object boundary. Here we show that when a fluid is confined in nano-volume, delimited by non-interacting pore walls, its density is on average smaller than the bulk density. The heterogeneous distribution of fluid density results from the nano-confinement, and progressively weakens when the pore size increases: it disappears for pores larger than 5 nm. On the other side, the fluid density approaches the ideal gas values in the limit of very small pores. This effect should be distinguished from the well know heterogeneity of density of fluids adsorbed in nanopores, driven by the difference between the strength of fluid-fluid and fluid-pore wall interactions. The reported observation has non-trivial influence on evaluation of excess/total adsorption in nanopores, as these two quantities are calculated assuming the known – and homogeneous – bulk density of gas in the pore. Additionally, the gas density in the pores depends on the definition of the pore volume which is neither straightforward nor unique. We analyze this phenomenon on an example of five gases: H2, CH4, the two intensively studied energy vectors, and N2, Ar, and Kr, commonly used for characterization of porous structures. Two model pore geometries with not adsorbing soft walls are analyzed (slit-shaped and cylindrical). For H2, the distributions of densities of gas confined in adsorbing and not adsorbing pores are compared and commented.

International audience;

International audience; With the demography growth, there is a huge pressure on protein demand, and the development of plant based proteins is required for a future sustainable food production. Plant proteins are efficient to stabilize interfaces in foams or emulsions, and the understanding of physical mechanisms at the origin of their interfacial behavior is important to develop new products. We investigate the adsorption of wheat grains (gliadin) and sunflower seeds (helianthinin) proteins, at air-water and oil-water interfaces, respectively. A combination of tensiometry, dilatational viscoelasticity and ellipsometry measurements is used to determine the adsorption mechanisms, and characterize the structure and properties of the interfacial protein films formed with different bulk protein concentrations. We demonstrate that a diffusion-controlled adsorption occurs at low bulk protein concentration for helianthinin whereas this mechanism occurs whatever the bulk concentration for gliadins. Surface pressure-induced film relaxation through conformation changes of proteins at the air-water interface is identified for gliadin whereas surface aggregation is observed at high helianthinin concentration. Overall, our experimental results highlight that structural flexibility of proteins appears as a key factor for their interfacial activity.

International audience; A molecular machine, or nanomachine, refers to any nano-sized system that produces quasi-mechanical movements (output) in response to a specific stimuli (input). Nano-engineering is today a rapidly growing, innovative field of science and technology. The 2016 Nobel Prize in Chemistry recompensing the chemical research effort in this area confirmed that engineering of the nano-machines is not any more an object of science-fiction stories. We are at the advent of new engineering methodology, in which the nano-systems can be numerically designed and chemically synthesized. In order to construct a complex machine, several challenging problems must be solved. First, a number of pre-assembled building blocks have to be prepared, as the function of the device is intended to be a consequence of their assembly. Furthermore, to obtain a predetermined function of the machine, this assembly should provide a possibility to precisely controlled translational and rotational movements of the machine components, stimulated by an inflow of external energy. The machine also needs an interface with its environment. Ultimately, it should be able to overcome thermal fluctuation (Brownian motion) that influences its mechanical action, and to operate out of equilibrium in dissipative systems, when controlled and driven by an external fueling, by light or other energy source.Starting from Richard Feynman prediction from 1984 that it would be possible to build machines with nanometric dimensions we show how the notion of the nano-machine has evolved during the last century. In 1983 chemists succeeded to produce molecular chains, catenanes, in which ring-shaped molecules were linked together by mechanical bonds, but the interlocked molecules did not form any intermolecular, strong covalent bonds. The catenanes were not only a new class of macromolecules: they also represented the first step towards creating a molecular machine. Then, in 1994 a rotaxane, a ring-shaped molecule that is mechanically attached to an axle has been created. The first molecular motor was proposed in 1999. Since then the rotaxane has been used to construct numerous molecular machines, including a molecular elevator, which can raise itself 0.7 nanometers above a surface, and an artificial muscle (2000), that is able to bend a very thin gold lamina. Many new ideas have been published and many new systems have been already synthesized. This presentation will be focused on the nanomachines in which the light is used as a photonic factor actuating and allowing control of the nano-machines movements.

International audience; Upon pH stimulus, double hydrophilic block copolymers form polyion complexes (PIC) in the micellar form. We used PIC micelles as ecofriendly templates for the synthesis of ordered mesoporous materials. The porosity of the final material is revealed by simple inversion of the pH stimulus. Various mesoporous silica materials have been obtained from cubic to lamellar.The control over the structure of the final material is expected to relate to the lyotropic behavior just as observed when micelles of amphiphilic molecules are used as template. However such lyotropic behavior has never been reported for PIC micelles. Moreover the same PIC leads to different structured silica materials depending on the physico-chemical conditions.Using X-rays and light scattering, optical microscopy and osmometry, we establish the equation of state (osmotic pressure vs volume fraction) of a PEO-b-PAA/oligoamine electrostatic complex. Its lyotropic behavior is characterized by a transition of shape at 0.16 w/w and a transition to a lamellar phase at 0.30w/w. The water content of the core of the micelles is addressed from the complete phase diagram of the polyelectrolyte complex in its coacervate form and explains why a single complex leads to porous material of different structure.

International audience;

International audience; A versatile and eco-compatible preparation route of functional ordered mesoporous materials will be described. It relies on the use of assemblies of hydrophilic diblock copolymers, in place of classical amphiphilic templates, as new structuring and functionalizing agents for the direct synthesis, at room temperature and in water, of polymer-functionalized mesoporous silica.The new structuring agents are dynamic PolyIon electrostatic Complex (PIC) micelles formed between double-hydrophilic-block-copolymers (DHBC) (constituted of a neutral block and an ionizable one) and an oppositely charged homopolyelectrolyte, which can be considered as an auxiliary of micellization of DHBC polymers.The different advantages of using PIC micelles are the following: due to their sensitivity to physicochemical parameters, PIC micelles allowed obtaining various hybrid mesostructures (cubic, 2D-hexagonal, lamellar...) by simply adjusting the material synthesis conditions using a unique DHBC/homopolyelectrolyte system. This is a consequence of the adjustable composition and water content of the polyion complex phase. The micellization process, which can be controlled by pH or ionic strength, is reversible in water and this allowed the recovery and recycling of the porogen polymers.Very interestingly, the use of PIC micelles permitted the direct preparation of polymer-functionalized mesopores. This was possible due to the easy dissociation of the polyion complex within the pores, selectively releasing the auxiliary of micellization while the DHBC remained for functionalizing the pores. This new method ensures an homogeneous functionalization of the mesopores, a control of the functional polymer chain lengths and a sufficient mesoporous volume. Moreover, the properties of the functional chains could be varied (acid, basic, metal-complexing...). Finally, this preparation route was extended to bio-functional hybrid mesophases useful as drug delivery systems [3] The direct formation of drug-loaded polymer-functionalized mesoporous materials was developed by using drug-polymer complex micelles as structuring agents ; this was shown with antibiotics exhibiting a pH-triggered release. Furthermore, studies are currently under way to estimate the catalytic performances of the new functional materials.

International audience; Despite being by far among the most widespread interface on Earth, with a pervasive presence in environment, biology, industry and daily life, physical phenomena at Air-Water Interface (AWI) are still largely elusive. This fact is related to the complexity of AWI with its peculiar electrostatic and flow boundary conditions. In this paper, we present a study of the dynamics and interactions of charged microparticles diffusing at submicrometric distances from an AWI. An interferometric set-up mounted on a microscope gives access to an highly resolved trajectory of the colloid (5-10 nm). Contrary to other established techniques (like TIRM and holography) our technique has the great advantage of allowing the measure of the absolute particle-interface distance. In order to control the electrostatic we use different concentration of salt and different pH in association with pH dependent charged microparticles.Surprisingly new equilibrium distances from the AWI are measured not accounted by established theories. In addition different drags corresponding to different boundaries conditions are found for same combination of particle and AWI depending on the particle’s motion direction namely perpendicular or parallel to the AWI.

International audience; Unlike macroscopic objects, any system of nanometric size shows characteristics that strongly depend on its size and geometric form. It is the consequence of the fact that the major part of atoms (or molecules) of nano-object is located at its surface, and their cohesive energy is smaller than for the atoms in the bulk. Here we show that when a fluid is confined in nano-volume, delimited by non-interacting pore walls, its density is heterogeneous, decreases close to the pore wall, and, on average, is smaller than the density of bulk fluid. The heterogeneity of distribution of fluid density, resulting from the nano-confinement, progressively weakens when the pore size increases, and totally disappears for pores larger than 5 nm. On the other side, in the limit of very small pores, the fluid density approaches the ideal gas value. This effect should be distinguished from the well know heterogeneity of density of fluids adsorbed in nanopores, driven by the difference between the strength of fluid-fluid and fluid-pore wall interactions, that varies with the distance from the pore wall. The reported observation has non-trivial influence on evaluation of excess/total adsorption in nanopores, as these two quantities are calculated assuming the known – and homogeneous – bulk density of gas in the pore. Additionally, the gas density in the pores depends on the definition of the pore volume which is neither straightforward nor unique. The right estimation of both: pore volume and gas density is essential for quantitative interpretation of experimental adsorption isotherms: evaluation of pore size distribution and of the amount of adsorbed gas. We analyze this problem on an example of five gases: H2, CH4, the two intensively studied energy vectors, and N2, Ar, and Kr, commonly used for characterization of porous structures. For H2, the distributions of densities of gas confined in adsorbing and not adsorbing pores are compared and commented. This work was supported by the French National Research Agency ANR, grant HYSTOR no. ANR-14-CE05-0009.

We study the intrinsic optical spectroscopy (UV-vis-NIR absorption, Raman and photoluminescence) signatures of single wall carbon nanotubes (SWNT) dispersed in degassed water without additives, so called ‘‘eau de nanotubes” (EdN). They are found to be very close to those of SWNT dispersed in aqueous suspensions stabilized with surfactants. Absorption peaks appear to be even slightly better resolved for EdN, suggesting sharper excitonic resonances, which is also supported by the Raman data. On the other hand, the photoluminescence signal is significantly weaker. These signatures suggest that SWNT are dispersed as individuals in degassed water, in a similar way single layer graphene was recently shown to be readily dispersable in degassed water [1-3].References[1]G. Bepete et al, Nat. Chem. 2016, DOI 10.1038/NCHEM2669[2]G. Bepete et al, J. Phys. Chem. C 2016, 120 (49), 28204–28214.[3]G. Bepte et al, Phys. Stat. Solidi 2016, 10 (12), 895-899.

International audience; Quantum sensing with diamond