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International audience; A full 3D analysis of the hierarchical porosity in Coscinodiscus sp. diatom structures was carried out by using a multiscale approach that combines three advanced volumetric imaging techniques with resolutions and fields of view covering all the porous characteristics of such complex architectures: electron tomography, "slice and view" approach that uses a dual-beam microscope (FIB-SEM), and array tomography consisting of serial imaging of ultrathin specimen sections. This multiscale approach allowed the whole porosity network to be quantified and provided an unprecedented structural insight into these natural nanostructured materials with internal organization ranging from micrometer to nanometer. The analysed species is made of several nested layers with different pore sizes, shapes and connectivities and characterized by the presence of interconnected pores structured in various ways. The first evidence of the presence of a nanometric porosity made of ellipsoidal pores in the siliceous diatom frustules is also provided.

International audience; We carry out random walk simulations on prototypical porous structures that are representative of actual hierarchical silica-based materials. The main throughput of the mesoscopic simulations proposed here is the tortuosity defined as the ratio of the fluid mean square displacements calculated in the absence and in the presence of the porous medium. This is a rigorous mathematical definition that has the advantage to be comparable to the ratio of self-diffusion coefficients for the bulk and confined fluid, which can be directly determined by means of diffusion experiments. Such tortuosity can also be compared with the ratio of bulk and effective electrical conductivities. These calculations are applied here to hierarchical materials such as those encountered in chromatography, membrane science or catalysis. The simulation results are compared to experimental data as well as to effective equations-such as Maxwell's equation-which are often invoked to infer tortuosity expressions based on effective mean field theories.

Source rocks are expected to become increasingly important in the upcoming years for oil and gas production as well as for the storage of greenhouse gases. These rocks are bedded and heterogeneous ...

We propose a set of simple formulae for interpreting “mercury cyclic porosimetry” measurements where multiple intrusion–extrusion cycles are carried out. By employing two parameters α ∈ [ 0 , 1 ] and κ ∈ [ 0 , 1 ] , our theory quantitatively breaks down any hysteresis observed in cyclic porosimetry data into contributions due to connectivity effects and contact-angle hysteresis, respectively. In particular, the parameter α , called “pore-space accessivity”, characterizes any serial connectivity between different-size pores. It has long been recognized that the standard method for determining the pore-size distribution (PSD) from mercury intrusion data based on the capillary bundle assumption overestimates the fraction of smaller pores; that corresponds to the α → 1 limit of our model. In contrast, for materials with α 1 , our theory predicts a broadened PSD shifted toward larger radii, thus representing a simple way of rectifying PSDs for connectivity effects. The proposed model also establishes mercury cyclic porosimetry as a standard experimental procedure for measuring α , which can then be used in continuum models of porous media where connectivity effects play a significant role, such as in multiphase flow.

International audience; We study the aggregation of charged plate-like colloids, Na-montmorillonite clays, in the presence of ionenes, oppositely charged polymer chains. The choice of the charged polymer allows tuning its linear charge density to match/mismatch the average charge separation on the clay surfaces. We assess the nanoscale structure of the aggregates formed by small-angle X-ray and neutron scattering. The nanoscale features of the formed clay aggregates are dominated by the presence of a stacking peak, giving clear evidence for the formation of clay tactoids, that is, a face-to-face aggregation geometry of the clay platelets. The chain charge density of ionenes influences not only the stacking repeat distance within the clay tactoids but also the extent of stacking and abundance of the tactoids. We may distinguish two regimes as a function of clay and ionene polymer charge densities (ρc and ρp, respectively). The first regime applies to ρp > ρc and ρp ≈ ρc, that is, for highly and “matching” charged chains. Under these conditions, the intercalated chains lie in a flat conformation within the tactoids, irrespective of the ionic strength (within the range studied, i.e., up to 0.05 M NaBr). For weakly charged chains, ρp < ρc, undulation of the ionene chains within the tactoid is seen. The degree of undulation increases with ionic strength due to the decreasing persistence length of the ionene chains. The extent of stacking (5–10 platelets per tactoid) is a general feature of all the systems, and its origin remains unknown. The system corresponding to the closest match in charge separations on the clay surface and on the polymer chain (ρp ≈ ρc) features the highest abundance of tactoids. This coincides with the highest macroscopic density as deduced from simple visual inspection of sediment volumes. This leads to the open question regarding the link between the density at the nanoscale and the macroscopic density and sedimentation behavior of the aggregate.

Owing to their complex morphology and surface, disordered nanoporous media possess a rich diffusion landscape leading to specific transport phenomena. The unique diffusion mechanisms in such solids stem from restricted pore relocation and ill-defined surface boundaries. While diffusion fundamentals in simple geometries are well-established, fluids in complex materials challenge existing frameworks. Here, we invoke the intermittent surface/pore diffusion formalism to map molecular dynamics onto random walk in disordered media. Our hierarchical strategy allows bridging microscopic/mesoscopic dynamics with parameters obtained from simple laws. The residence and relocation times – tA, tB – are shown to derive from pore size d and temperature-rescaled surface interaction ε/kBT. tA obeys a transition state theory with a barrier ~ε/kBT and a prefactor ~10−12 s corrected for pore diameter d. tB scales with d which is rationalized through a cutoff in the relocation first passage distribution. This approach provides a formalism to predict any fluid diffusion in complex media using parameters available to simple experiments., The diffusion of fluids in complex nanoporous geometries represents a challenge for modelling approaches. Here, the authors describe the macroscopic diffusivity of a simple fluid in disordered nanoporous materials by bridging microscopic and mesoscopic dynamics with parameters obtained from simple physical laws.

International audience; Hypothesis: The objective is to elucidate the multiscale dynamics of water within natural mixtures of minerals, green earth pigments that are mainly composed of phyllosilicates containing large amount of iron. In particular, the interaction of water with the different kinds of surfaces has to be probed. One issue is to examine the influence of surface type, basal or edge, on the dispersion quality.Experiment: The study was carried out using 1H variable field NMR relaxometry on various green earth pigment dispersions and concentrations. To analyse the data, a new analytical model was developed for natural phyllosilicates containing large amount of paramagnetic centres.Finding: The proposed theoretical framework is able to fit the experimental data for various samples using few parameters. It allows to determining water diffusion and residence times in complex phyllosilicate dispersions. Furthermore, it makes it possible to differentiate the contribution of the basal and edge surfaces and their respective surface area in interaction with water. Moreover, NMR relaxation profile reveals to be highly sensitive to the structural aspect of the phyllosilicates and to the accessibility of water to iron, hence allowing to discriminate clearly between two very similar phyllosilicates (glauconite and celadonite) that are difficult to distinguish by standard structural methods.

International audience; Wax deposition is one of the major concerns for waxy crude oil production and transportation. A better understanding and prediction of fluid properties related to this issue require knowledge of the medium structuration at scales ranging from nanometers (molecules) to a few micrometers (crystals). For this purpose, the behavior of a waxy crude oil in the bulk was compared to that of a model oil over a wide range of temperatures above and below the wax appearance temperature. The combined use of cross-polarized microscopy (CPM) and the implementation of innovative techniques for the field such as small- and wide-angle X-ray scattering and low-field nuclear magnetic resonance has provided a more precise idea of the structure of these two types of fluids. If the nature of the orthorhombic crystals and their lamellar shape are identical for both fluids, a very appreciable difference is highlighted in their chain axis dimensions. The n-paraffin crystal size is larger than 120 nm in the model oil. In crude oil, it is only about 1–10 nm with a long-range order in the directions perpendicular to the chain axis and a monomolecular thickness in the chain axis. Moreover, from the model oil CPM images, we observed aggregates of lamellar shape crystals. Because the model oil does not contain asphaltenes and resins, the crystals are larger and the branches divide significantly less than in crude oil, which results in a trapped liquid proton population unobservable in the model oil. All these observations give a vision of the structure of n-paraffin crystals. It is made of aggregates of relatively dense lamellae in the center and more aerated lamellae at the periphery, which split into several branches.

International audience; During cement hydration, C–S–H nanoparticles precipitate and form a porous and heterogeneous gel that glues together the hardened product. C–S–H nucleation and growth are driven by dissolution of the cement grains, posing the question of how cement grain surfaces induce spatial heterogeneities in the formation of C–S–H and affect the overall microstructure of the final gel. We develop a model to examine the link between these spatial gradients in C–S–H density and the time-evolving effective interactions between the nanoparticles. Using a combination of molecular dynamics and Monte Carlo simulations, we generate the 3D microstructure of the C–S–H gel. The gel network is analyzed in terms of percolation, internal stresses, and anisotropy, and we find that all of these are affected by the heterogeneous C–S–H growth. Further analysis of the pore structure encompassed by the C–S–H networks shows that the pore size distributions and the tortuosity of the pore space show spatial gradients and anisotropy induced by the cement grain surfaces. Specific features in the effective interactions that emerge during hydration are, however, observed to limit the anisotropies in the structure. Finally, the scattering intensity and specific surface area are computed from the simulations in order to connect to the experimental methods of probing the cement microstructure.

International audience; The confined dynamics of water molecules inside a pore involves an intermittence between adsorption steps near the interface and surface diffusion and excursions in the pore network. Depending on the strength of the interaction in the layer(s) close to the surface and the dynamical confinement of the distal bulk liquid, exchange dynamics can vary significantly. The average time spent in the surface proximal region (also called the adsorption layer) between a first entry and a consecutive exit allows estimating the level of ‘nanowettablity’ of water. As shown in several seminal works, NMRD is an efficient experimental method to follow such intermittent dynamics close to an interface. In this paper, the intermittent dynamics of a confined fluid inside nanoporous materials is discussed. Special attention is devoted to the interplay between bulk diffusion, adsorption and surface diffusion on curved pore interfaces. Considering the nano or meso length scale confinement of the pore network, an analytical model for calculating the inter-dipolar spin–lattice relaxation dispersion curves is proposed. In the low-frequency regime (50 KHz–100 MHz), this model is successfully compared with numerical simulations performed using a 3D-off lattice reconstruction of Vycor glass. Comparison with experimental data available in the literature is finally discussed.

International audience; This study deals with the role of the alumina nanoporous texture in the accessibility of the asphaltene molecules to the active sites of resid hydroconversion catalysts. We have proposed in this contribution to investigate the diffusion and adsorption process into the porosity of various monomodal and bimodal alumina supports. It consists of immersing catalytic supports, under the form of extrudates, into an asphaltene solution in toluene. Optical microscopy observations of a cut of the cylindrical extrudates were carried out to follow the asphaltene penetration as a function of the contact time. We aimed at reaching a good asphaltene mass balance, taking into account (i) the evolution of the asphaltene concentration in solution and (ii) the precise determination of the amount of asphaltenes deposited into the support. The influence, on the mass transfer and the penetration depth, of various parameters such as temperature, asphaltene concentration of the solution, asphaltene size polydispersity, and alumina porous texture was appraised. The novelty of this Article resides in the evaluation of diffusion and adsorption of asphaltenes at high temperature (250 °C). Finally, an endeavor for the process modeling is presented. The adsorption equilibrium was modeled according to the Langmuir-type isotherm. A model considering the radial diffusion in a cylinder (the extrudate) was used providing an average diffusion coefficient.

International audience; The upgrading of heavy petroleum fractions needs the development of more and more efficient heterogeneous catalysts. One of the major issues of these processes is the diffusion of asphaltenes to the active site through the porous network of the alumina support. The catalytic efficiency is deeply impacted by the transport phenomena and the interfacial interactions. The aim of this work is to capture the extent to which low-field 2D 1H NMR relaxation time correlations can contribute to a better understanding of the dynamics of asphaltene in solution and within the pores of catalyst supports. 2D T1-T2 maps for asphaltenes in solution in toluene exhibit several T1-T2 contributions, varying with the asphaltene concentration and the size of the asphaltenic fractions obtained by ultrafiltration separation. According to the nano-aggregate structure proposed by the Yen-Mullins aggregation model of asphaltenes, it was possible to unravel the different asphaltenic proton relaxation behaviors. By the use of NMR relaxometry, we have confirmed that water is a wetting solvent of the alumina instead of the toluene which is a nonwetting solvent. The presence of macropores in catalyst clearly boosts the toluene mobility through the porous network. 2D T1-T2 maps for asphaltenes inside the pores show various types of protons, all of them with a severe constrained dynamics. Asphaltene nano-aggregates and clusters can be seen as large entities jammed into the pores, slowly mobile and affecting the solvent (toluene) mobility. When macroporosity exists in the support, the asphaltene overcrowding is less sensitive, enabling a faster dynamics of asphaltenes and toluene.

International audience; In this study, the flocculation and the subsequent decantation step of mixed suspensions of 10 nm-sized γ-Fe2O3 magnetic nanoparticles and 500 nm-sized beidellite clay platelets was investigated. This work may find application in the field of water treatment, specifically the flocculation processes with magnetically assisted sedimentation. After a short description of the preparation and characterization of the raw materials (nanoparticles and clays), the influence of several parameters (pH, concentrations of nanoparticles and clays etc.) on the amount of flocculated materials was examined, which gave information on the concentration ranges allowing a complete flocculation, together with a better understanding on the interactions between nanoparticles and clays responsible for flocculation. The optimal conditions for magnetically assisted settling were then determined by comparing for each sample sedimentation velocities under gravity and in the presence of a Nd-Fe-B magnet. Finally, the complex multiscale structure of the flocs in water was explored, through the measurement of several bulk properties (zeta-potential and volume measurements, laser granulometry), while the organization of the materials at a microscopic scale was investigated by cryo-transmission electron microscopy (cryo-TEM) and small-angle X-ray scattering (SAXS).

Two dimensional ultra thin CdSe nanoplatelets have attracted a large interest due to their optical properties but their formation mechanism is not well understood. Several different mechanisms have been proposed: confined growth in a surfactant mesophase acting as a template, anisotropic ripening of small seeds into 2D nanoplatelets or continuous anisotropic growth of a limited number of nuclei. However, quantitative in situ data that could validate or disprove these formation scenarios are lacking. We use synchrotron-based small-angle and wide-angle X-ray scattering to probe the formation mechanism of CdSe nanoplatelets synthesized using a heating-up method. We prove the absence of a molecular mesophase in the reactive medium at the onset of nanoplatelet formation ruling out a templating effect. We also show that our data are inconsistent with the anisotropic ripening of small seeds whereas the evolution of the SAXS patterns during the reaction is consistent with the continuous lateral growth of nanoplatelets fed by reactive monomers. Finally, we show that when the final temperature of the synthesis is lowered, nanoplatelets with larger lateral dimensions form. We reveal that they bend in solution during their growth to yield nanoscrolls.

Two dimensional ultra thin CdSe nanoplatelets have attracted a large interest due to their optical properties but their formation mechanism is not yet well understood. Several different mechanisms and models have been proposed but quantitative in situ data that could validate or disprove them are lacking. We use synchrotron-based small-angle and wide-angle X-ray scattering to probe in situ the formation mechanism of CdSe nanoplatelets synthesized using a heating-up method. We prove the absence of a molecular mesophases in the reactive medium at the onset of nanoplatelet formation ruling out a templating effect. A q-2 regime is observed from the start of the reaction which extends towards smaller wave vectors with time, consistent with the continuous lateral growth of nanoplatelets from a limited number of seeds fed by reactive monomers. A ripening mechanism where small cluster fuse to yield nanoplatelets can also be ruled out by our data. When the final temperature is lowered, larger nanoplatelets are obtained and the SAXS patterns exhibit marked oscillations due to their rolling into curved nanoscrolls. Our experiments thus show that nanoplatelet curvature appears during their synthesis.

International audience; This contribution couples (a) Small angle X‐ray scattering (SAXS) experiments of a high‐performance concrete (HPC) at the millimetric scale, and (b) Focused ion beam/scanning electron microscopy (FIB/SEM) of the cement paste of the HPC, with 10‐20 nm voxel size. The aim is to improve the understanding of the 3D pore network of the HPC at the mesoscale (tens of nm), which is relevant for fluid transport. The mature HPC is an industrial concrete, based on pure Portland CEMI cement, and planned for use as structural elements for deep underground nuclear waste storage. Small angle X‐ray scattering patterns are computed from the 3D pore images given by FIB/SEM (volumes of 61‐118 μm3). They are positively correlated with SAXS measurements (volumes of 5 mm3). Aside from correlations with FIB/SEM data, experimental SAXS allows to investigate a wider range of effects on the pore structure. These are mainly the HPC drying state, the presence of aggregates (by analyzing data on cement paste alone), and the use of Poly Methyl MethAcrylate resin impregnation.

International audience; Interactions between kaolinite (KGa-2) and a typical anionic surfactant bis(2-ethylhexyl) sulfosuccinate sodium (AOT) have been study to obtain a better knowledge of this system. Firstly, adsorption isotherms of AOT on kaolinite are realized as a function of pH. Stability experiments have been performed between the surfactant and the clay mineral and the bed sediments structure have been studied with Small Angle X-ray Scattering (SAXS). In acidic media, the shape of the adsorption isotherm leads to the following suggestions: firstly, for surfactant concentration below the CMC a surfactant monolayer is adsorbed on the positively charged edge surfaces, and then, for surfactant concentrations above the CMC, a bilayer is adsorbed on the edge surfaces. Consequently, in the first case, the surface becomes hydrophobic and in the second case, the surface becomes hydrophilic and this assumption is verified with hydrophobicity tests. Under alkaline conditions no surfactant is adsorbed on surfaces confirming the adsorption on the edge surfaces in acidic conditions. In agreement, with previous studies [1,2] significant stabilization of kaolinite suspensions can be observed in the presence of high surfactant concentration, in both pH conditions. Finally, structural studies by SAXS provide data about the organization of particles in the bed sedimentation.

This chapter presents several experimental examples in which the water dynamics close to a colloidal interface can be probed by nuclear magnetic relaxation dispersion (NMRD). Three classes of systems are presented: a porous plaster exhibiting large flat surfaces, a colloidal gel of finite clay particles and a suspension of very long and rigid nanorods. For these three colloidal systems, the spin–lattice relaxation is driven by intra-dipolar or quadrupolar magnetic interactions. At low magnetic field, the relaxation is essentially sensitive to the rotational dynamics of the water molecule and the time evolution of the surface director probed by the molecule during its self-diffusion. To model these experiments, we propose an analytical model of the intermittent dynamics of water involving successive excursions in the confined bulk and relocation/adsorption on the colloidal surface. This analytical approach is uniquely based on the use of temporal first-passage statistics. For water, we show how NMRD experiments provide an original characterization of the surface nano-wettability, being also sensitive to the particle geometry.

Analysing the structure and microstructure of compacted swelling clay minerals is important because of the applications of these minerals in engineering and environmental sciences. Given the typical sub-micrometre size of the particles and pores in clays, small-angle scattering techniques are well suited for such analysis. Interpretation of the intensity patterns, however, remains complex, especially in the intermediate region between the first Bragg peak and the small-angle range. In this study, theoretical small-angle neutron scattering and neutron diffraction patterns are calculated for three-dimensional virtual porous media representative of packed swelling clay particles (i.e. 0.1–0.2 µm size fraction of vermiculite). This packing represents the distribution of the size, shape and particle orientation of a bulk vermiculite sample, for which experimental scattering/diffraction patterns were also collected. It was found that a good fit between the experimental and calculated scattering/diffraction profiles can be obtained only if the presence of crystal-structure defects in the particles is considered. The existence of such defects was supported by transmission electron microscopy analysis. Their influence on power law exponents extracted from intensity profiles is assessed in detail. The analysis is further extended to the influence of mineral dehydration and particle orientation on the intensity profiles. This work shows that using virtual porous media as toy models makes it possible to evaluate the roles of different microstructural parameters in the extent of variation of power law exponents. Such knowledge can be used for better interpretation of small-angle scattering data of natural compacted swelling clay-rich media.

International audience; Imaging the distribution of reactive molecules in an internal diffusion-limited catalyst is of primary importance in the comprehension and modeling of these systems. Mesoporous alumina supports were impregnated with asphaltenes in a self-pressurized autoclave at high pressure (5 MPa) and high temperature (523 K). Extrudates were then analyzed by laser-induced breakdown spectroscopy (LIBS). We showed that LIBS can provide quantitative concentration maps of sulfur , nickel and vanadium in the ppm range. Processing of these maps is proposed to obtain one-dimensional profiles of the penetration of these elements. These profiles show that the penetration of asphaltenes into the catalyst support is a very complex process. These findings contribute to improving the comprehension of internal diffusion-limited processes, particularly the hy-drodemetallization (HDM) process of oil residues. This report also indicates that LIBS-based 2 imaging represents a powerful tool for quickly providing two-dimensional elemental maps over a large dynamic range, i.e., typically from ppm to tens of %, thereby opening up opportunities for innumerable applications in the field of catalysis.

We show that nuclear magnetic relaxation experiments at variable magnetic fields (NMRD) provide noninvasive means for probing the spatial dependence of liquid diffusion close to solid interfaces. These experiments performed on samples of cylindrical and spherical nanopore geometries demonstrate that the average diffusion coefficient parallel to the interface is proportional to the pore radii in different dynamics regimes. A master curve method allows extraction of gradients of diffusion coefficients in proximity of the pore surfaces, indicative of the efficiency of coupling between liquid layers. Due to their selectivity in frequency, NMRD experiments are able to differentiate the different water dynamical events induced by heterogeneous surfaces or composed dynamical processes. This analysis relevant in physical and biological confinements highlights the interplay between the molecular and continuous description of fluid dynamics near interfaces.

Heavy oil fractions can be upgraded through various processes, such as catalytic residue hydrotreatments. Mass transfer of macromolecules present in the heavy oil fraction, so-called asphaltenes, from feedstock to catalytic active sites is limited during hydroprocesses. Mechanisms of the diffusion of asphaltenes through pore network, adsorption, and pore plugging are no well-known under process conditions. A new method has been developed to characterize and investigate asphaltene diffusion phenomenon in catalysts under a high temperature and pressure. Alumina supports immersed in asphaltene solution are left to evolve at 250 °C and 5.0 MPa. Solutions and supports are analyzed to quantify the mass transfer, penetration depth, and change in support porosity of asphaltenes. This procedure was evaluated in terms of reproducibility and sensitivity. The impact of several parameters, such as pressure, was appraised. With this powerful procedure, for the first time, asphaltene diffusion without conversion into th...

International audience; Natural and manufactured disordered systems are ubiquitous and often involve hierarchical structures. This structural organization optimizes defined physical properties at several scales from molecular to representative volumes where the usual homogenization approach becomes efficient. For studying a particular physical property on these systems it is thus required to use a general method of analysis based on the joint application of complementary techniques covering the whole set of time-and length-scales. Here we review a comprehensive multiscale method presented for analyzing the three-dimensional moisture transport in hierarchical porous media such as synthesized reference silicates and cement-based materials. Several techniques (NMR spectroscopy, relaxometry, diffusometry, X-ray micro-tomography, conductivityaEuro broken vertical bar) have been used to evidence the interplay between the different scales involved in this transport process. This method allows answering the general opened questions concerning the scale dependence of such a moisture transport in cement-based materials. We outline the main results of the multiscale techniques applied on reference porous silicates allowing separating the impact of geometry, hydric state and wettability on the moisture transport. Based on this approach, we prove that this transport at micro- and meso-scale is determinant to modify the moisture at macro-scale during setting or for hardened cement-based materials.

The effect of polymer coating on MNR relaxometry of maghemite nanoparticles has been studied. The samples were carefully sorted by size in order to reach narrow size distribution (r1 and r2 increase with nanoparticle diameter. We have analysed the role of polydispersity for nanoparticles with the same mean size on the dispersion curves. We have compared the role of coating on nanoparticles NMR relaxivity between bare and poly(sodium acrylate-co-maleate) coated nanoparticles. We have investigated the influence of nanoparticle size on the T1 and T2 activation energy Ea. While Ea decreases with nanoparticle diameter when determined from T1, it increases from T2 determination. The influence is more important for small particles (9 nm). Moreover, the PAAMA coating changes the energy Ea obtained from T2: Ea becomes independent of the nanoparticle diameter. These results highlight the need of a complete characterisation of the role of the coating on the relaxation of magnetic particles.

Flocculation and its tuning are of utmost importance in the optimization of several industrial protocols in areas such as purification of waste water and civil engineering. Herein, we studied the polyelectrolyte-induced flocculation of clay colloids on a model system consisting of purified clay colloids of well-defined size fractions and ionene polyelectrolytes presenting regular and tunable chain charge density. To characterize ionene-induced clay flocculation, we turned to the combination of light absorbance (turbidity) and ζ-potential measurements, as well as adsorption isotherms. Our model system allowed us to identify the exact ratio of positive and negative charges in clay-ionene mixtures, the (c+/c-) ratio. For all samples studied, the onset of efficient flocculation occurred consistently at c+/c- ratios significantly below 1, which indicated the formation of highly ionene-deficient aggregates. At the same time, the ζ-potential measurements indicated an apparent zero charge on such aggregates. Thus, the ζ-potential values could not provide the stoichiometry inside the clay-ionene aggregates. The early onset of flocculation in clay-ionene mixtures is reminiscent of the behavior of multivalent salts and contrasts that of monovalent salts, for which a large excess amount of ions is necessary to achieve flocculation. Clear differences in the flocculation behavior are visible as a function of the ionene charge density, which governs the conformation of the ionene chains on the clay surface.

Cryo-soft X-ray microscopy is an emerging imaging tool complementary to cryo-electron microscopy, allowing to image frozen hydrated specimens ten to hundred times thicker, but at lower resolution. We describe how the method, so far restricted to isolated small cells or cell monolayers, can be extended to large cells and tissue. We image the synapses of the Kenyon cells in frozen hydrated Drosophila brains combining cryo-soft X-ray microscopy of thick vitreous sections, and cryo-electron microscopy of ultrathin vitreous sections. We show how to obtain frozen hydrated sections of thicknesses ranging from 40 nm up to 2.5 μm, by tuning the sectioning speed of the cryo-microtome. A fluorescent stereo-microscope mounted on the cryo-microtome allowed us to target the regions of interest after GFP-labeling of synapses. Thick cryo-sections were imaged by cryo-soft X-ray microscopy at a resolution better than 25 nm, while ultrathin cryo-sections of the same regions were explored in parallel at the nanometre level of resolution by cryo-electron microscopy.

International audience; There is currently a growing interest in nano-structured silica based materials due to their remarkable thermal properties. These materials are notably used in Vacuum Insulating Panels (VIP). Their exceptional insulating performances have been demonstrated experimentally for a relatively long time. But the heat transfer mechanisms occurring in this kind of materials remain relatively badly known due to the nanometric dimensions and to the complexity of the porous structure. Therefore, the present study aims to develop a numerical model for estimating the magnitude of conductive heat transfer inside nano-structured silicas using a realistic representation of their complex porous structure. The model takes into account the special porous morphology of the materials at both the nanometric and microscopic scale. Moreover, the conduction heat transfer at the nanometric scale is treated using a numerical resolution of the Boltzmann equation since the validity of the macroscopic laws is then questionable. The computations are conducted using phonon properties of silica obtained in the literature. A parametric study allows us to analyse the influence of structural characteristics and thermo-physical properties on the insulating performances and thus to highlight the most important parameters.

International audience; The coagulation of sodium montmorillonite by inorganic salts (NaNO3, Ca(NO3)(2) and La(NO3)(3)) was studied by combining classical turbidity measurements with wide-angle-X-ray scattering (WAXS), small-angle-X-ray scattering (SAXS), and transmission X-ray microscopy (TXM). Using size-selected samples, such a combination, associated with an original quantitative treatment of TXM images, provides a true multiscale investigation of the formed structures in a spatial range extending from a few angstroms to a few micrometers. We then show that, at neutral pH and starting with fully Na-exchanged samples, coagulation proceeds via the formation of stacks of particles with a slight mismatch between layers. These stacks arrange themselves into larger porous anisotropic particles, the porosity of which depends on the valence of the cation used for coagulation experiments. Face-face coagulation is clearly dominant under those conditions, and no evidence for significant face-edge coagulation was found. These structures appear to arrange as larger clusters, the organization of which should control the mechanical properties of the flocs.

Mechanical behavior of concrete crucially depends on cement hydrates, the "glue" of cement. The design of high performance and more environmentally friendly cements demands a deeper understanding of the formation of the multiscale structure of cement hydrates, when they precipitate and densify. We investigate the precipitation and setting of nano-grains of cement hydrates using a combination of Monte Carlo and Molecular Dynamics numerical simulations and study their texture from nano up to the micron scale. We characterize the texture of cement hydrates using the local volume fraction distribution, the pore size distribution, the scattering intensity and the chord length distribution and we compare them with experiments. Our nano-granular model provides cement structure with realistic texture and mechanics and can be further used to investigate degradation mechanisms. © 2017 The Authors, published by EDP Sciences

This paper discusses the applicability of neutron imaging techniques for probing the internal microstructure of several fossil woods upon wetting and drying, two phenomena occurring in museum cabinets and endangering the fossil woods. Investigations were carried out using lignites (fossil woods) from two French localities (Rivecourt, Parisian Basin, Oise – Paleogene; Angeac, Aquitanian Basin, Charente – Cretaceous), which present different macroscopic behavior upon drying. Thanks to the high sensitivity of neutrons to hydrogen content, it was possible to track water diffusion through 3 mm thick samples and to follow in situ changes related to either supply or withdrawal of water without any special preparation and in a relevant time range (from 1 min to a few hours). Classical image analysis allows discriminating between the behavior of the two fossil woods with regard to their interaction with water. Further analysis based on a Fourier transform of projection images provides additional information regarding the existence of large pores in one of the samples. Differences in pore network and internal structures have important mechanical consequences as one of the samples retains its integrity upon drying, whereas the other one shatters into pieces. A better understanding of the underlying processes will clearly require multi-scale analyses, using additional techniques that could probe the materials at a lower scale. Such a combination of multi-scale analyses should provide valuable information for a better conservation of wood remnants, which is crucial for both paleobotanical research and museum exhibits.

International audience; Strength and other mechanical properties of cement and concrete rely upon the formation of calcium-silicate-hydrates (C-S-H) during cement hydration. Controlling structure and properties of the C-S-H phase is a challenge, due to the complexity of this hydration product and of the mechanisms that drive its precipitation from the ionic solution upon dissolution of cement grains in water. Departing from traditional models mostly focused on length scales above the micrometer, recent research addressed the molecular structure of C-S-H. However, small-angle neutron scattering, electron-microscopy imaging, and nanoindentation experiments suggest that its mesoscale organization, extending over hundreds of nanometers, may be more important. Here we unveil the C-S-H mesoscale texture, a crucial step to connect the fundamental scales to the macroscale of engineering properties. We use simulations that combine information of the nanoscale building units of C-S-H and their effective interactions, obtained from atomistic simulations and experiments, into a statistical physics framework for aggregating nanoparticles. We compute small-angle scattering intensities, pore size distributions, specific surface area, local densities, indentation modulus, and hardness of the material, providing quantitative understanding of different experimental investigations. Our results provide insight into how the heterogeneities developed during the early stages of hydration persist in the structure of C-S-H and impact the mechanical performance of the hardened cement paste. Unraveling such links in cement hydrates can be groundbreaking and controlling them can be the key to smarter mix designs of cementitious materials.

Cellular processing of nanomaterials may affect their physical properties at the root of various biomedical applications. When nanoparticles interact with living cells, their spatial distribution is progressively modified by cellular activity, which tends to concentrate them into intracellular compartments, changing in turn their responsivity to physical stimuli. In this paper, we investigate the consequences of cellular uptake on the related magnetic properties and NMR relaxivity of iron oxide nanoparticles. The superparamagnetic behavior (field-dependent and temperature-dependent magnetization curves investigated by SQUID (Superconducting Quantum Interference Device) measurements) and nuclear magnetic relaxation dispersion (NMRD) R1 profiles of citrate-coated maghemite nanoparticles (mean diameter 8 nm) were characterized in colloidal suspension and after being uptaken by several types of cells (tumor cells, stem cells and macrophages). The temperature-dependent magnetization as well as the NMRD profile were changed following cellular uptake depending on the stage of endocytosis process while the field-dependent magnetization at room temperature remained unchanged. Magnetic coupling between nanoparticles confined in cell lysosomes accounts for the modification in magnetic behavior, thereby reflecting the local organization of nanoparticles. NMR longitudinal relaxivity was directly sensitive to the intracellular distribution of nanoparticles, in line with Transmission Electron Microscopy TEM observations. This study is the first attempt to link up magnetic properties and NMR characterization of iron oxide nanoparticles before and after their cell processing. Copyright © 2012 John Wiley & Sons, Ltd.

This paper summarizes the principal aims, content and conclusions of a document recently submitted to IUPAC, as a Technical Report, by the IUPAC Working Group on “Liquid intrusion and alternative methods for the characterization of macroporous materials” and to be published in full in Pure and Applied Chemistry. The initial goal of the group was to list, examine and compare the methods presently used to characterize macroporous structures. In addition to mercury porosimetry, the most popular experimental techniques include the intrusion of various non-wetting and wetting liquids, capillary condensation, liquid permeation, imaging and image analysis. The statistical reconstruction of porous materials and the use of macroporous reference materials are also examined. A particular aim is to evaluate the status of mercury porosimetry, since the use of mercury raises a number of safety and environmental issues. The scope and limitations of each method are examined in the context of the scientific and technological requirements and the applicability of some new and unfamiliar methods is also discussed. Finally, an indication is given of the likely direction of future developments in the methodology of macropore characterization.

Physical separation of heavy oils and bitumen is of particular interest because it improves the description of the chemical and structural organization in these industrial and challenging fluids (Zhao, B.; Shaw, J. M.Composition and size distribution of coherent nanostructures in Athabasca bitumen and Maya crude oil. Energy Fuels 2007, 21, 2795−2804). In this study, permeates and retentates, differing in aggregate concentrations and sizes, were obtained from nanofiltration of a vacuum residue at 200 °C with membranes of varying pore size. Elemental composition and density extrapolations show that aggregates are best represented as n-pentane asphaltenes, while the dispersing phase corresponds to n-pentane maltenes. Small-angle X-ray scattering (SAXS) measurements are processed, on this basis, to calculate the size and mass of the aggregates. Aggregates in the vacuum residue are similar in size and mass to asphaltenes in toluene, and temperature elevation decreases the size of the aggregates. Wide-angle X-r...

This document deals with the characterization of porous materials having pore widths in the macropore range of 50 nm to 500 μm. In recent years, the development of advanced adsorbents and catalysts (e.g., monoliths having hierarchical pore networks) has brought about a renewed interest in macropore structures. Mercury intrusion–extrusion porosimetry is a well-established method, which is at present the most widely used for determining the macropore size distribution. However, because of the reservations raised by the use of mercury, it is now evident that the principles involved in the application of mercury porosimetry require reappraisal and that alternative methods are worth being listed and evaluated. The reliability of mercury porosimetry is discussed in the first part of the report along with the conditions required for its safe use. Other procedures for macropore size analysis, which are critically examined, include the intrusion of other non-wetting liquids and certain wetting liquids, capillary condensation, liquid permeation, imaging, and image analysis. The statistical reconstruction of porous materials and the use of macroporous reference materials (RMs) are also examined. Finally, the future of macropore analysis is discussed.

Temperature-dependent rheological behavior of heavy oils and bitumen is usually modeled with a colloidal approach, taking into account a temperature-dependent solvation effect (Storm, D. A.; Barresi, R. J.; Sheu, E. Y.Rheological study of Ratawi vacuum residue in the 298–673 K temperature range. Energy Fuels 1995, 9, 168−176). In addition to viscosity measurements for vacuum residue at various asphaltene contents, in the present study, we make use of small-angle X-ray scattering (SAXS) data on the 80–240 °C temperature range to propose an interpretation on asphaltene aggregation, consistent with both approaches. The radius of gyration Rg and molecular weight MW of asphaltenes in a vacuum residue are measured and are of the same magnitude as asphaltenes in toluene. Dimensions and masses decrease with the temperature, while the small length scale remains unchanged, reinforcing the hierarchical aggregation scheme previously described in toluene. These findings enrich the viscosity data interpretation. A solv...

Complementary neutron and X-ray small angle scattering results give prominent information on the asphaltene nanostructure. Precise SANS and SAXS measurements on a large q-scale were performed on the same dilute asphaltene-toluene solution, and absolute intensity scaling was carried out. Direct comparison of neutron and X-ray spectra enables description of a fractal organization made from the aggregation of small entities of 16 kDa, exhibiting an internal fine structure. Neutron contrast variation experiments enhance the description of this nanoaggregate in terms of core-shell disk organization, giving insight into core and shell dimensions and chemical compositions. The nanoaggregates are best described by a disk of total radius 32 Å with 30% polydispersity and a height of 6.7 Å. Composition and density calculations show that the core is a dense and aromatic structure, contrary to the shell, which is highly aliphatic. These results show a good agreement with the general view of the Yen model (Yen, T. F.; et al. Anal. Chem.1961, 33, 1587-1594) and as for the modified Yen model (Mullins, O. C. Energy Fuels2010, 24, 2179-2207), provide characteristic dimensions of the asphaltene nanoaggregate in good solvent.

Reversed micelles and water in oil micro-emulsions can be used to solubilize biopolymers and genetic materials allowing analyzing their properties in a confined geometry. Nuclear Magnetic Resonance Dispersion (NMRD) provides a powerful and a noninvasive experimental technique to probe the long-term dynamics of these confined systems. However, the first step is to analyze and understand the slow dynamics of water inside these micro-reactors without any guest molecule. This is the aim of this presentation. Experimental results have been obtained for deuteron 2 H NMRD of water confined in reverse micelles of bis (2-ethylhexyl) sodium sulfosuccinate (AOT) dispersed in isooctane C 8 H 18 . The water content is expressed as the molar ratio W 0 = [Water] / [AOT]. The radius of the spherical reversed micelles, R m , increases almost linearly with W 0 . In our case, W 0 is chosen in the range 20 ≤ W 0 ≤ 50 (35 ≤ R m ≤ 80 A). The frequency dependence for the spin-lattice relaxation rate R 1 (ω) exhibits two regimes, for all W 0 values: a plateau at low frequency, proportional to 1/ R m , followed by the beginning of an algebraic decay. These experimental observations are discussed and compared to a numerical simulation of the intermittent Brownian diffusion of a water molecule inside a rotating reverse micelle. The possibility to probe some properties of the confinement, such as the localisation time on the sulfonated palisade and/or the water self-diffusion inside the water pool is emphasised.

We report on proton NMR relaxation of hardened and aged grey and white CEM I paste with several controlled degree of relative humidity. A proton NMR relaxation study of these two CEM I cement pastes shows very different pore size hierarchies for these two materials. The good sensitivity of the proposed method for analysing the evolution of the pore size dependencies under drying and wetting history of the material could be very useful for studying the durability of building material under severe conditions of use.

The purpose of this work was to understand how fractal dimension of two-dimensional (2D) trabecular bone projection images could be related to three-dimensional (3D) trabecular bone properties such as porosity or connectivity. Two alteration processes were applied to trabecular bone images obtained by magnetic resonance imaging: a trabeculae dilation process and a trabeculae removal process. The trabeculae dilation process was applied from the 3D skeleton graph to the 3D initial structure with constant connectivity. The trabeculae removal process was applied from the initial structure to an altered structure having 99% of porosity, in which both porosity and connectivity were modified during this second process. Gray-level projection images of each of the altered structures were simply obtained by summation of voxels, and fractal dimension (Df) was calculated. Porosity (phi) and connectivity per unit volume (Cv) were calculated from the 3D structure. Significant relationships were found between Df, phi, and Cv. Df values increased when porosity increased (dilation and removal processes) and when connectivity decreased (only removal process). These variations were in accordance with all previous clinical studies, suggesting that fractal evaluation of trabecular bone projection has real meaning in terms of porosity and connectivity of the 3D architecture. Furthermore, there was a statistically significant linear dependence between Df and Cv when phi remained constant. Porosity is directly related to bone mineral density and fractal dimension can be easily evaluated in clinical routine. These two parameters could be associated to evaluate the connectivity of the structure.

We describe the phase behavior of an aqueous mixture of discotic nanoparticles of laponite and spherical magnetic nanoparticles of maghemite. To obtain stable mixtures from a chemical point of view, the maghemite nanoparticles are first coated by a thin layer of silica in order to adapt their surface chemistry to that of laponite nanoparticles: this enables one to raise volume fractions of maghemite Phi mag in the laponite suspensions up to several percent. Although the system is out of equilibrium, a "fluid-solid" state diagram was established showing that the mixtures undergo a fluid-solid transition, similar to that of pure suspensions of laponite, over a given volume fraction of laponite Phi lap and over a given Phi mag. An increase in Phi mag shifts Phi lap toward the lower values. When a solid sample is just above Phi lap, the application of an external magnetic field gradient induces a solid-to-liquid transition if the sample is located not too far from Phi lap on the state diagram. The structure of the mixtures, determined either at small scale by small-angle neutron scattering (SANS) or at intermediate scales by optical microscopy, shows that the solid samples are phase separated at a local scale: they are made of densely connected domains of laponite nanoparticles surrounding liquid pockets of maghemite nanoparticles. The size of the pockets grows with time. The magnetic liquid pockets are responsible for the rupture of the solid samples when an external magnetic field gradient is applied since their deformation induces local mechanical stress, internally damaging the network formed by the solid domains of laponite. The microscopic phase separation is the result of two opposite effects: (i) entropic effects that tend to phase separate the system macroscopically when the packing entropy overcomes the orientational entropy and (ii) long-range electrostatic repulsions that freeze the system.

International audience; Relaxivities r1 and r2 of cobalt ferrite magnetic nanoparticles (MNPs) have been investigated in the aim of improving the models of NMR relaxation induced by magnetic nanoparticles. On one hand a large set of relaxivity data has been collected for cobalt ferrite MNP dispersions. On the other hand the relaxivity has been calculated for dispersions of cobalt ferrite MNPs with size ranging from 5 to 13 nm, without using any fitting procedure. The model is based on the magnetic dipolar interaction between the magnetic moments of the MNPs and the 1H nuclei. It takes into account both the longitudinal and transversal contributions of the magnetic moments of MNPs leading to three contributions in the relaxation equations. The comparison of the experimental and theoretical data shows a good agreement of the NMR profiles as well as the temperature dependence.

The dynamic behavior of water within two types of ionomer membranes, Nafion and sulfonated polyimide, has been investigated by field-cycling nuclear magnetic relaxation. This technique, applied to materials prepared at different hydration levels, allows the proton motion on a time scale of microseconds to be probed. The NMR longitudinal relaxation rate R(1) measured over three decades of Larmor angular frequencies omega is particularly sensitive to the host-water interactions and thus well-suited to study fluid dynamics in restricted geometries. In the polyimide membranes, we have observed a strong dispersion of R(1)(omega) following closely a 1/square root omega law in a low-frequency range (correlation times from 0.1 to 10 micros). This is indicative of a strong interaction of water with "interfacial" hydrophilic groups of the polymeric matrix (wetting situation). Variations of the relaxation rates with water uptake reveal a two-step hydration process: solvation and formation of disconnected aqueous clusters near polar groups, followed by the formation of a continuous hydrogen bond network. On the contrary, in the Nafion we observed weak variations of R(1)(omega) at low frequencies. This is typical of a nonwetting behavior. At early hydration stages, R(1)(omega) evolves logarithmically, suggesting a confined bidimensional diffusion of protons in the microsecond time range. Such an evolution is lost at higher swelling where a plateau related to three-dimensional diffusion is observed.

International audience; Supercapacitors are electrochemical devices which store energy by ion adsorption on the surface of a porous carbon. They are characterized by high power delivery. The use of nanoporous carbon to increase their energy density should not hinder their fast charging. However, the mechanisms for ion transport inside electrified nanopores remain largely unknown. Here we show that the diffusion is characterized by a hierarchy of time scales arising from ion confinement, solvation, and electrosorption effects. By combining electrochemistry experiments with molecular dynamics simulations, we determine the in-pore conductivities and diffusion coefficients and their variations with the applied potential. We show that the diffusion of the ions is slower by 1 order of magnitude compared to the bulk electrolyte. The desolvation of the ions occurs on much faster time scales than electrosorption.

We have investigated the dynamics of fragile glass forming orthoterphenyl confined in nanoporous materials with different surface properties. The dynamics on the nanosecond timescale were probed with neutron spin echo measurements. The intermediate scattering functions were fitted using a stretched exponential and a background. This background, due to molecules forming an interfacial layer at the surface of the pore that are immobile at the nanosecond time scale, depends on the surface properties of the porous materials and increases with decreasing temperature. The dynamics of the confined liquid depends on fluid–wall interactions: the dynamics are slower in a weakly attractive silica-walled material with 7.1 nm pores (∼9 molecular diameters) than in a hydrophobic material with 6.3 nm pores (∼8 molecular diameters). Adsorption times of 1 μs and 690 ns at 298 and 323 K for oTP confined in silica-walled nanoporous materials were calculated from nuclear magnetic resonance field cycling relaxometry experiments.

Nous presentons les variations avec le champ magnetique des vitesses de relaxation spin-reseau (R 1 ) des protons et deuterons de l'eau confinee dans des micelles inverses formees par le melange d'un tensioactif bis (2-ethylhexyl) sodium sulfosuccinate (AOT), de l'isooctane et de l'eau. Apres un plateau a tres bas champs, R 1 diminue en loi de puissance lorsque la frequence de Larmor augmente. Nous avons interprete ce comportement en frequence a l'aide d'un modele de relaxation de spin impliquant une reorientation moleculaire couplee a une translation en confinement spherique. Une simulation numerique de dynamique brownienne de molecules d'eau confinees dans une sphere est proposee et comparee aux resultats experimentaux. Cette etude constitue une etape preliminaire vers une meilleure comprehension de la dynamique lente de systemes biologiques en confinement.

Porous materials, concentrated colloidal suspensions are examples of confining systems developing large specific surface and presenting a rich variety of shapes. Such an interfacial confinement strongly influences the molecular dynamics of embedded fluids and the diffusive motion of entrapped Brownian particles. An individual trajectory near the interface can be described as an alternate succession of adsorption steps and random flights in the bulk. Statistical properties of these random flights in various interfacial confining systems are needed as prerequisites in order to understand the full transport process. Related to first passage processes, these properties play a central role in numerous problems such as the mean first exit time in a bounded domain, heterogeneous catalytic reactivity and nuclear magnetic relaxation in complex and biological fluids. In the present work, we first consider the various possibilities of connecting two points of a smooth interface by a random flight in the bulk. Second, we analyse from the theoretical and experimental points of view a way to probe Brownian flight statistics. From the experimental point of view, we investigate the slow fluid dynamics near some colloidal interfaces by field-cycling NMR relaxometry. This is a way to follow slow dynamical correlations from 1?ns to 10??s. This spectroscopy appears to be a good choice, considering that the algebraic nature of the probability of the first return to a surface builds a long-time memory. The experimental part confirms that the embedded fluid dynamics is sensitive to possible morphologic crossover and provides information about interface geometry. We also believe that such an approach can be used to probe interfacial dynamics by itself, for example in the case of a colloidal system undergoing a phase transition (dynamical arrest, rotational blockage,...).