Interfaces, Confinement, Matériaux et Nanostructures

Abstract Metasedimentary rocks generally contain carbonaceous material (CM) deriving from the evolution of organic matter originally present in the host sedimentary rock. During metamorphic processes, this organic matter is progressively transformed into graphite s.s. and the degree of organisation of CM is known as a reliable indicator of metamorphic grade. In this study, the degree of organisation of CM was systematically characterised by Raman microspectroscopy across several Mesozoic and Cenozoic reference metamorphic belts. This degree of organisation, including within‐sample heterogeneity, was quantified by the relative area of the defect band (R2 ratio). The results from the Schistes Lustrés (Western Alps) and Sanbagawa (Japan) cross‐sections show that (1) even through simple visual inspection, changes in the CM Raman spectrum appear sensitive to variations of metamorphic grade, (2) there is an excellent agreement between the R2 values calculated for the two sections when considering samples with an equivalent metamorphic grade, and (3) the evolution of the R2 ratio with metamorphic grade is controlled by temperature ( T ). Along the Tinos cross‐section (Greece), which is characterised by a strong gradient of greenschist facies overprint on eclogite facies rocks, the R2 ratio is nearly constant. Consequently, the degree of organisation of CM is not affected by the retrogression and records peak metamorphic conditions. More generally, analysis of 54 samples representative of high‐temperature, low‐pressure to high‐pressure, low‐temperature metamorphic gradients shows that there is a linear correlation between the R2 ratio and the peak temperature [ T (°C) = −445 R2 + 641], whatever the metamorphic gradient and, probably, the organic precursor. The Raman spectrum of CM can therefore be used as a geothermometer of the maximum temperature conditions reached during regional metamorphism. Temperature can be estimated to ± 50 °C in the range 330–650 °C. A few technical indications are given for optimal application.

Abstract The sea provides a large variety of seaweeds that, because of their chemical composition, are fantastic precursors of nanotextured carbons. The carbons are obtained by the simple pyrolysis of the seaweeds under a nitrogen atmosphere between 600 and 900 °C, followed by rinsing the product in slightly acidic water. Depending on the origin of the seaweed and on the pyrolysis conditions, the synthesis may be oriented to give an oxygen‐enriched carbon or to give a tuned micro/mesoporous carbon. The samples with a rich oxygenated surface functionality are excellent as supercapacitor electrodes in an aqueous medium whereas the perfectly tuned porous carbons are directly applicable for organic media. In both cases, the specific surface area of the attained carbons does not exceed 1300 m 2 g −1 , which results in high‐density materials. As a consequence, the volumetric capacitance is very high, making these materials more interesting than activated carbons from the point of view of developing small and compact electric power sources. Such versatile carbons, obtained by a simple, ecological, and cheap process, could be well used for environment remediation such as water and air treatment.

This Perspective provides a critical analysis of the current knowledge concerning solvent vapor annealing (SVA) of block polymer thin films. Herein, we identify key challenges that will be important to overcome for future development of SVA as a practical, reliable, and universal technique for the valorization of block polymer thin films in a wide range of technologies. The Perspective includes a brief background on thin film block polymer self-assembly, a historical account of the SVA technique, an overview of the SVA fundamentals that are necessary to develop a more comprehensive picture of the overall process, and summaries of relevant and important contributions from the recent literature. We also offer our outlook on SVA and suggest important future directions.

Abstract A novel microporous templated carbon material doped with nitrogen is synthesized by using a two‐step nanocasting process using acrylonitrile (AN) and propylene as precursors, and Na–Y zeolite as a scaffold. Liquid‐phase impregnation and in situ polymerization of the nitrogenated precursor inside the nanochannels of the inorganic scaffold, followed by gas‐phase impregnation with propylene, enables pore‐size control and functionality tuning of the resulting carbon material. The material thereby obtained has a narrow pore‐size distribution (PSD), within the micropore range, and a large amount of heteroatoms (i.e., oxygen and nitrogen). In addition, the carbon material inherits the ordered structure of the inorganic host. Such features simultaneously present in the carbon result in it being ideal for use as an electrode in a supercapacitor. Although presenting a moderately developed specific surface area ( S BET = 1680 m 2 g –1 ), the templated carbon material displays a large gravimetric capacitance (340 F g –1 ) in aqueous media because of the combined electrochemical activity of the heteroatoms and the accessible porosity. This material can operate at 1.2 V in an aqueous medium with good cycleability—‐beyond 10 000 cycles—and is extremely promising for use in the development of high‐energy‐density supercapacitors.

Tensile tests were carried out on free-standing composite films of poly(vinyl alcohol) and six different types of carbon nanotubes for different nanotube loading levels. Significant increases in Young's modulus by up to a factor of 2 were observed in all cases. Theories such as the rule-of-mixtures or the Halpin-Tsai-theory could not explain the relative differences between composites made from different tube types. However, it is possible to show that the reinforcement scales linearly with the total nanotube surface area in the films, indicating that low diameter multiwall nanotubes are the best tube type for reinforcement. In addition, in all cases crystalline coatings around the nanotubes were detected by calorimetry, suggesting comparible polymer−nanotube interfaces. Thus, the reinforcement appears to be critically dependent on the polymer−nanotube interfacial interaction as previously suggested.

Abstract Both crystallization and melting experiments have been carried out on two natural, biotite-muscovite (DK) and tourmaline-muscovite (GB) High Himalayan leucogranites (HHL) at 4 kbar, logfO2 = FMQ−0·5, aH2O = 1−0⋅03, and at five temperatures between 803 and 663°C H2O contents of the quenched glasses were analysed by ion microprobe. Plagioclase and biotite are the liquidus phases for reduced melt H2O contents and H2O-rich conditions, respectively. H2O saturation limits range from ∼8 to 10 wt%. DK has a wider crystallization interval than GB (150 vs 80°C for conditions close to H2O saturation), and a slightly higher H2O-saturated solidus (645 compared with 630°C for GB). Tourmaline never crystallized spontaneously from the melt. Tourmaline seeds always reacted out to biotite in the biotite-muscovite sample, whereas they remained stable in the tourmaline-muscovite sample. Biotite is replaced by hercynite as the main ferromagnesian phase at high temperature and reduced aH2O. Muscovite crystallization is restricted to near-solidus conditions. The compositions of plagioclase, alkali feldspar, biotite and muscovite are given as a function of bulk composition, temperature and aH2O. Glass compositions are richer in normative quartz than the 4 kbar H2O-saturated Qz–Ab–Or eutectic, and become more peraluminous and less mafic with increasing fractionation. Biotite crystallization in peraluminous liquids is favoured by elevated Fe, Mg and Ti contents. Muscovite crystallization is not promoted under H2O-saturated conditions. Tourmaline stability is strongly dependent on aH2O. For GB, tourmaline is present at elevated temperatures for intermediate values of aH2O (803° C, ∼0–7), but not above 650°C for H2O-saturated conditions. Comparison of the natural crystallization sequence with experiments suggests initial water contents between 5 and 7·5 wt % for the DK magma, and > 7 wt% for the GB magma. Plagioclase core compositions give minimum temperatures of ∼700°C for GB and 750°C for DK, consistent with an emplacement of these HHL as almost entirely liquid bodies. The restricted occurrence of biotite in the GB granite suggests that it reacted out during the magmatic evolution, owing to a marked change in fO2 toward more oxidizing conditions. Tourmaline leucogranites can be generated from biotite leucogranites by fractional crystallization under conditions of increasing degree of oxidation.

This study investigates the large voltage range of symmetric carbon/carbon capacitors in environmentally friendly aqueous lithium sulfate electrolyte. A high over-potential related to the hydrogen sorption mechanism at the negative electrode contributes usefully to enhance the operating voltage up to 1.9 V with an excellent stability during 10 000 charge/discharge cycles. Such a voltage value is two times higher than the values generally demonstrated with symmetric carbon/carbon capacitors in conventional aqueous media, while avoiding the disadvantages of the corrosive properties of acidic and basic electrolytes. Temperature programmed desorption analysis of the electrodes after long-term cycling gives the evidence that the maximum voltage is essentially limited by an irreversible electro-oxidation process at the positive electrode. If the potential of the positive electrode goes beyond a given value during cell operation, a massive electro-oxidation of carbon leads to a further deleterious increase of the maximum potential of the electrode and an increase of electrode resistance resulting in a decrease of capacitance. Inconvenience can be sidestepped by performing a controlled chemical oxidation of the carbon surface using hydrogen peroxide. As a consequence, the maximum potential of the electrode remains stable during operation of the cell at 1.9 V, and the system can be charged/discharged during 10 000 cycles with very moderate loss of capacitance or increase of resistance.

Relations between thermodynamics, structural, and mechanical properties of Laponite suspensions were recently discussed in the literature. One important issue concerning the liquid/gel transition of the Laponite suspensions is to understand why a mechanical gel appears concomitantly with what appears as an incomplete nematic transition. To get some insight, we first give a more extended characterization of the viscoelastic properties of these suspensions near the liquid/gel transition. For this purpose, stress relaxation experiments are compared to direct determinations of the viscoelastic modulus in the frequency domain. This permits the following of viscoelastic properties, in the linear regime, on a very extended scale, from 10-5 to 102 rad/s. The data show that the relaxation mechanisms are very slow and are compatible with the presence of a large scale structural organization compared to the elementary particle size. The elastic modulus follows the power law: G‘ = A(C − C0)α. Only the concentration threshold varies with the ionic strength. In a second part, we compare, on the same system, how the osmotic pressure and the birefringent properties are correlated. As already shown by Gabriel et al., three optical domains can be defined, an isotropic liquid, an isotropic gel, and a birefringence gel, where numerous threadlike defects highly reminiscent of nematic texture are observed. An interesting new result is seen, a line that separates the isotropic and the birefringent gel coincides with the line where the plateau of the osmotic pressure ends up. Recalling that the osmotic plateau starts just at the liquid/solid transition, we propose a more complete phase diagram exhibiting a pseudobiphasic region with no macroscopic phase separation.

A new type of supercapacitor electrode is reported, prepared by pressing a carbon nanotube/polyacrylonitrile blend and then pyrolyzing the pellet (see Figure). Although their specific surface area is very low, e.g., 200 m2 g–1, the C/C composites demonstrate high values of capacitance, up to 100 F g–1. The authors propose two explanations for these remarkable values.

Brindley et al. (1951) reported the earliest efforts to obtain international collaboration on nomenclature and classification, initiated at the International Soil Congress in Amsterdam in 1950. Since then, national clay groups were formed, and they proposed various changes in nomenclature at group meetings of the International Clay Conferences. Most of the national clay groups have representation on the Nomenclature Committee of the Association Internationale Pour L’Etude des Argiles (AIPEA, International Association for the Study of Clays) Nomenclature Committee, which was established in 1966, and no longer have ad hoc nomenclature committees. The precursor committee to the AIPEA Nomenclature Committee was the Nomenclature Subcommittee of the Comite Internationale Pour L’Etude Des Argiles (CIPEA, International Committee for the Study of Clays). The AIPEA Nomenclature Committee has worked closely with other international groups, including the Commission on New Minerals and Mineral Names (CNMMN) of the International Mineralogical Association (IMA), which is responsible for the formal recognition of new minerals and mineral names, and the International Union of Crystallography (I.U.Cr), which considered extensions to the nomenclature of disordered, modulated and polytype structures (Guinier et al., 1984) published earlier by a joint committee with the IMA (Bailey, 1977). In contrast to the other national clay groups, however, The Clay Minerals Society (CMS) Nomenclature Committee, which was established in 1963 at the same time as the CMS and predates the AIPEA Nomenclature Committee, remains in existence and occasionally produces recommendations. The precursor to this committee was the Nomenclature Sub-Committee, which was organized in 1961 by the (U.S.) National Research Council. The Chair of the AIPEA Nomenclature Committee is a standing member of the CMS Nomenclature Committee so that the committees are in close contact. The purpose of the AIPEA Nomenclature Committee has been to make general and specific recommendations concerning a) definitions of mineralogical and crystallographic clay-related terms, b) classification and terminology of clays, clay minerals and related terms, c) standardization of structural and descriptive terms, d) species, subgroup, and group names, e) the establishment of procedures/criteria for determining species, f) the emphasis (or re-emphasis) of the proper use of terms, and g) any additional aspects relating to nomenclature. Approximately twelve published reports have been presented since the 1950s. However, an additional twelve unpublished reports have been archived, and many committee papers have been written by guest members asked to join the committee to help resolve a specific issue or by committee members to help lead the discussion of a specific topic. Although the latter papers have not been published, many illuminate the rationale behind recommendations. In addition, they may also show insight in areas still in need of additional research. In general, the Committee is not expected to provide research to reach a recommendation. Instead, where sufficient data are unavailable, the Committee may (or may not) note the insufficiency and postpone any further comment. Thus, extensive committee papers may have been written, only to conclude that comment should be deferred.

The combination of neutron diffraction with isotopic substitution (NDIS) experiments and molecular dynamics (MD) simulations to characterize the structuring in an aqueous solution of the denaturant guanidinium chloride is described. The simulations and experiments were carried out at a concentration of 3 m at room temperature, allowing for an examination of any propensity for ion association in a realistic solution environment. The simulations satisfactorily reproduced the principal features of the neutron scattering and indicate a bimodal hydration of the guanidinium ions, with the N-H groups making well-ordered hydrogen bonds in the molecular plane, but with the planar faces relatively deficient in interactions with water. The most striking feature of these solutions is the rich ion-ion ordering observed around the guanidinium ion in the simulations. The marked tendency of the guanidinium ions to stack parallel to their water-deficient surfaces indicates that the efficiency of this ion as a denaturant is due to its ability to simultaneously interact favorably with both water and hydrophobic side chains of proteins.

We present a constrained reverse Monte Carlo method for structural modeling of porous carbons. As in the original reverse Monte Carlo method, the procedure is to stochastically change the atomic positions of a system of carbon atoms to minimize the differences between the simulated and the experimental pair correlation functions. However, applying the original reverse Monte Carlo method without further constraints yields nonunique structures for carbons, due to the presence of strong three-body forces. In this respect, the uniqueness theorem of statistical mechanics provides a helpful guide to the design of reverse Monte Carlo methods that give reliable structures. In our method, we constrain the bond angle distribution and the average carbon coordination number to describe the three-body correlations. Using this procedure, we have constructed structural models of two highly disordered porous carbons prepared by pyrolysis of saccharose at two different temperatures. The resulting pair correlation functions are in excellent agreement with those obtained by diffraction experiments. Simulated transmission electron microscopy (TEM) images of the resulting models are compared to experimental images. Many of the features observed in the experimental images are also observed in the simulations. The model carbons are characterized by determination of the porosity, pore size distribution, adsorbent−adsorbate potential energy distribution, and adsorption properties at zero coverage, using a model of nitrogen as the adsorbate. Grand canonical Monte Carlo simulations of nitrogen adsorption in the model materials are presented, and it is found that the results can be explained in terms of the adsorbent−adsorbate potential energy distribution but not in terms of the pore size distribution. For both models, the isosteric heat of adsorption is a decreasing function of coverage, in agreement with typical experimental results in other porous carbons.

Abstract The objective of the present study was to investigate changes in the structural, textural, and surface properties of tubular halloysite under heating, which are significant in the applications of halloysite as functional materials but have received scant attention in comparison with kaolinite. Samples of a purified halloysite were heated at various temperatures up to 1400°C, and then characterized by X-ray diffraction, electron microscopy, Fourier-transform infrared spectroscopy, thermal analysis, and nitrogen adsorption. The thermal decomposition of halloysite involved three major steps. During dehydroxylation at 500–900°C, the silica and alumina originally in the tetrahedral and octahedral sheets, respectively, were increasingly separated, resulting in a loss of long-range order. Nanosized (5–40 nm) γ-Al 2 O 3 was formed in the second step at 1000–1100°C. The third step was the formation of a mullite-like phase from 1200 to 1400°C and cristobalite at 1400°C. The rough tubular morphology and the mesoporosity of halloysite remained largely intact as long as the heating temperature was <900°C. Calcination at 1000°C led to distortion of the tubular nanoparticles. Calcination at higher temperatures caused further distortion and then destruction of the tubular structure. The formation of hydroxyl groups on the outer surfaces of the tubes during the disconnection and disordering of the original tetrahedral and octahedral sheets was revealed for the first time. These hydroxyl groups were active for grafting modification by an organosilane (γ-aminopropyltriethoxysilane), pointing to some very promising potential uses of halloysite for ceramic materials or as fillers for novel clay-polymer nanocomposites.

We have prepared hydrogenated single-wall and multiwall carbon nanotubes, as well as graphite, via a dissolved metal reduction method in liquid ammonia. The hydrogenated derivatives are thermally stable up to 400 °C. Above 400 °C, a characteristic decomposition takes place accompanied with the simultaneous formations of hydrogen and a small amount of methane. Transmission electron micrographs show corrugation and disorder of the nanotube walls and the graphite layers due to hydrogenation. The average hydrogen contents determined from the yield of evolved hydrogen correspond to the compositions of C11H for both types of nanotubes and C5H for graphite. Hydrogenation occurred even on the inner tubes of multiwall nanotubes as shown by the chemical composition and the overall corrugation. The thermal stability and structural results suggest the formation of C−H bonds in nanotubes and graphite.

There are several questions that are not well understood with respect to the long-term stability characteristics of lime-treated expansive soils in spite of being used as a conventional technique to improve the properties of expansive soils. This paper examines the long-term stability characteristics of FoCa bentonite soil (FoCa represents the first two letters of the two towns between which this type of soil is excavated: Fourgues and Cahaignes) using 4% lime treatment. The long-term stability characteristics referred to as durability in the paper were interpreted taking into account the influence of wetting–drying and freezing-thawing cycles on key engineering properties which include swelling and strength behavior of both untreated and lime-treated FoCa. In addition, leaching tests were carried out to study the Ca2+ions and pH concentration changes of the percolating water from both treated and untreated compacted expansive soil specimens analyze the permanence of the clay treatment. Finally, to highlight the changes induced in the texture of the material, pore size volume and distribution were investigated by mercury intrusion tests.

We study suspensions of synthetic clay Laponite at very low ionic strength. We show the existence, for these charged disk-like particles, of a liquid-soft solid transition mainly driven by electrostatic repulsive interactions. Such a process defines a re-entrant transition line in the phase diagram. Location of this line is predicted using basic arguments. The structure is characterized by ultra-small-angle X-ray scattering (USAXS). Soft-solid suspensions show a correlation peak compatible with long-range electrostatic stabilization. Such a result strongly contrasts with the evolution of the scattering spectra for solid-like suspensions of Laponite at high ionic strength (above 10−4 M). Close inspection of this correlation peak reveals that individual particle distribution is not homogeneous in space.

Nanostructured vanadium nitride/multiwalled carbon nanotubes (VN/CNTs) composites for pseudo-capacitor applications were obtained via the sol–gel synthesis of organic or inorganic vanadium oxide precursors followed by temperature programmed ammonia reduction. Nitrogen adsorption and impedance spectroscopy measurements showed that the incorporation of CNTs during VN synthesis allows VN/CNTs nanocomposites to be obtained with higher porosity, narrower pore size distribution, better conductivity and improved electrochemical properties compared to VN without CNTs. In particular, cyclic voltammetry using three-electrode cells in KOH shows that the contribution of the redox peaks is increased when VN is associated with the carbon nanotubes. As a consequence, a capacitance increase was measured in the two-electrode system. Another important advantage of using VN/CNTs composites is their high capacitance retention (58%) at high current density (30 A g−1) compared with VN (7%), resulting in an enhancement of the energy density at high power. All these positive aspects were significantly more marked when CNTs were incorporated during VN synthesis compared to a material resulting from the physical mixture of VN with CNTs. TEM, XPS and Raman analyses point out that the enhanced electrochemical performance observed with the VN/CNTs composite could be related to an intimate contact between VN and the CNT network, a homogeneous distribution of VN on CNTs and the presence of an open mesoporous texture favouring the access of the electrolyte to the active material surface.

A specific methodology was developed to collate the interlayer configurations resulting from Grand-Canonical Monte Carlo (GCMC) simulations with experimental X-ray and neutron diffraction data for two synthetic Na-saturated saponites having contrasting layer charge. Numerical simulations were performed assuming different existing sets of atomic partial charge and Lennard-Jones parameters for clay and water. For each parameter set and for the two samples in both the mono- and bihydrated states, the water contents resulting from GCMC simulations were first compared to water vapor desorption gravimetry data. The density distributions of interlayer species were then used to generate 00l intensities that were compared to X-ray and neutron diffraction data, the latter being recorded on both hydrogenated and deuterated specimens. The CLAYFF model [Cygan et al. J. Phys. Chem. B2004, 108, 1255] is shown to better account for water content and organization compared to the model developed by Skipper et al. (Clays Clay Miner.1995, 43, 285) and modified by Smith (Langmuir1998, 14, 5959). However, diffraction patterns calculated for bihydrated samples from CLAYFF simulations did not match satisfactorily the diffraction data. Lennard-Jones parameters were thus modified for oxygen atoms from the clay layer. When combined with the SPC/E water model, this modified version of CLAYFF allows matching experimental water contents and fitting the complete set of diffraction data. Relevant information may thus be derived on the influence of layer charge on the orientational properties of interlayer water molecules which differs for the different clay models. Finally, the approach used in the present study proved powerful for assessing atomic interaction parameters considered for computational simulations.

The aim of this paper is to find out new alternative materials that respond to sustainable development criteria. For this purpose, an original utilization of straw for the design of lightweight aggregate concretes is proposed. Four types of straw were used: three wheat straws and a barley straw. In the present study, the morphology and the porosity of the different straw aggregates was studied by SEM in order to understand their effects on the capillary structure and the hygroscopic behavior. The physical properties such as sorption-desorption isotherms, water absorption coefficient, pH, electrical conductivity and thermo-gravimetric analysis were also studied. As a result, it has been found that this new vegetable material has a very low bulk density, a high water absorption capacity and an excellent hydric regulator. The introduction of the straw in the water tends to make the environment more basic; this observation can slow carbonation of the binder matrix in the presence of the straw.

The origin of the long-term gelation of clay suspensions was recently questioned. We have investigated this problem by looking at the chemical stability of the laponite solid particles as a function of the preparation, the long-term storage, and the age of the suspensions. Under ambient atmosphere, ${\mathrm{Mg}}^{2+}$ is released from the laponite, suggesting that carbon dioxide from the atmosphere promotes acidification of the dispersions, resulting in a progressive laponite dissolution and a slow increase of the ionic strength. These factors induce a sol-gel transition, leading to the observation of fractal aggregates above the micrometric length scale. Such an evolution is not observed if the samples are carefully handled under ${\mathrm{N}}_{2}$ atmosphere for a long period of time. In these circumstances, the suspensions stay free of ${\mathrm{Mg}}^{2+}$ and undergo a fluid-solid transition along a defined transition line in the plane (volume-fraction--ionic-strength). In this situation, one interesting question concerns the unusual coincidence between a mechanical transition and an incomplete nematic transition.