Search

Imogolite nanotube (INT) is a fascinating one-dimensional (1D) material that can be synthesized in the liquid phase. Its behavior in solution is crucial for many applications and depends on the organization of water at the liquid-wall interface. We study here this water organization by using the nonlinear optical technique of polarization-resolved second harmonic scattering (SHS). A microscopic model is proposed to interpret the origin of the coherent SHS signal recovered in this 1D colloidal system. This work demonstrates that the SHS technique is able to probe the shell of water molecules oriented around the nanotubes. Water organization results from the electric field induced by the nanotube walls, and it is strongly dependent on the ionic strength of the suspension.

Imogolite nanotubes (INTs) form transparent aqueous nematic solutions, with strong birefringence and X-ray scattering power. They provide an ideal model system for studying the assembly of one-dimensional nanomaterials into fibres, as well as offering interesting properties in their own right. Here, in-situ polarised optical microscopy is used to study the wet spinning of pure INTs into fibres, illustrating the influence of process variables during extrusion, coagulation, washing and drying on both structure and mechanical properties. Tapered spinnerets were shown to be significantly more effective than thin cylindrical channels for forming homogeneous fibres; a result related to simple capilliary rheology by fitting a shear thinning flow model. The washing step has a strong influence of structure and properties, combining the removal of residual counter-ions and structural relaxation to produce a less aligned, denser and more networked structure; the timescales and scaling behviour of the processes are compared quantitatively. Both strength and stiffness are higher for INT fibres with a higher packing fraction and lower degree of alignment, indicating the importance of forming a rigid jammed network to transfer stress through these porous, rigid rod assemblies. The electrostatically-stabilised, rigid rod INT solutions were successfully cross-linked using multivalent anions, providing robust gels, potentially useful in other contexts.

Imogolite nanotubes present a unique spatial separation of conduction and valence bands but the large bandgap inhibits potential application as a photocatalyst. The first step toward using these well-defined nanotubes in photocatalysis and exploiting their natural polarization-promoting charge separation across the nanotubes wall, is to tune their bandgap energy. Here, titanium modified double walled aluminogermanate imogolite nanotubes are prepared to overcome this limitation. Structural and optical properties are determined at different scales and the photocatalytic performance is evaluated for H2 production under UV-visible light irradiation. Although the incorporation of Ti atoms into the structure remains limited, the resulting nanotubes reveal a remarkable hydrogen evolution rate of ~1500 µmol g-1 h-1, corresponding to a 65-fold increase relative to a reference TiO2P25 photocatalyst. These results confirm the theoretical predictions regarding the untapped potential of modified imogolite nanotubes as promising 1D photoactive polarized nanoreactors.

Doping liquid-crystal phases with nanoparticles is a fast-growing field with potential breakthroughs due to the combination of the properties brought by the two components. One of the main challenges remains the long-term stability of the hybrid system, requiring complex functionalization of the nanoparticles at the expense of their self-assembly properties. Here we demonstrate the successful synthesis of additive-free noble-metal nanoparticles at the surface of charged inorganic nanotubes. Transmission electron microscopy and UV-visible spectroscopy confirm the stabilization of metallic nanoparticles on nanotubes. Meanwhile, the spontaneous formation of liquid-crystals phases induced by the nanotubes is observed, even after surface modification with metallic nanoparticles. Small-angle X-ray scattering experiments reveal that the average interparticle distance in the resulting hybrids can be easily modulated by controlling electrostatic interactions. As a proof-of-concept, we demonstrate the effectiveness of our method for the preparation of homogeneous transparent hybrid films with a high degree of alignment.

International audience; Solid wetting-layers in inorganic nano-reactors: the water in imogolite nanotube case In 2016, 'isolated' water molecules trapped inside beryl nanochannels provided the fi rst fi rm experimental evidence of the dipole ordering of water molecules and a new 'quantum tunneling' state was evidenced. We have discovered a new phase of 'isolated' water molecules at the inner surface of inorganic nanotubes and we have investigated their associated dynamical properties. Our fi ndings are signifi cant to the emerging fi eld of 'isolated' nanoconfi ned water and to the areas of water science, nanoreactors and nanofl uidics. Inelastic neutron scattering and DFT-MD techniques are used in association with new methods of analysis which may be of interest to other fi elds of physics and nanosciences. By combined use of wide-angle X-ray scattering, thermo-gravimetric analysis, inelastic neutron scattering, density functional theory and density functional theory molecular dynamics simulations, we investigate the structure, dynamics and stability of the water wetting-layer in single-walled aluminogermanate imogolite nanotubes (SW Ge-INTs): an archetypal system for synthetically controllable and monodisperse nano-reactors. We demonstrate that the water wetting-layer is strongly bound and solid-like up to 300 K under atmospheric pressure, with dynamics markedly different from that of bulk water. Atomic-scale characterisation of the wetting-layer reveals organisation of the H 2 O molecules in a curved triangular sublattice stabilised by the formation of three H-bonds to the nanotube's inner surface, with covalent interactions sufficiently strong to promote energetically favourable decoupling of the H 2 O molecules in the adlayer. The evidenced changes in the local composition, structure, electrostatics and dynamics of the Ge-INT's inner surface upon the formation of the solid wetting-layer demonstrate solvent-mediated functionalisation of the nanotube's cavity at room temperature and pressure, suggesting new strategies for the design of nano-rectors towards potential control of chemical reactivity in nano-confined volumes.

International audience; In this article, we revisit the colloidal stability of clay imogolite nanotubes by studying the effect of electrostatic interactions on geo-inspired synthetic nanotubes in aqueous dispersions. The nanotubes in question are double-walled aluminogermanate imogolite nanotubes (Ge-DWINTs) with a well-defined diameter (4.3 nm) and with an aspect ratio around 4. Surface charge properties are assessed by electrophoretic measurements, revealing that the outer surfaces of Ge-DWINT are positively charged up to high pH values. Series of Ge-DWINT dispersions have been prepared by osmotic stress to control both ionic strength of the dispersion and the volume fraction in nanotubes. Optical observations coupled to Small and Wide-Angle X-ray Scattering (SAXS/WAXS) experiments allow us to unravel different nanotube organizations. At low ionic strength (IS < 10−2 mol.L−1), Ge-DWINTs are fully dispersed in water while they form an arrested gel phase above a given concentration threshold, which shifts towards higher volume fraction with increasing ionic strength. The swelling law, derived from the evolution of the mean intertube distance as a function of the nanotube concentration, evidences a transition from isotropic swelling at low volume fractions to one-dimensional swelling at higher volume fractions. These results show that the colloidal stability of Ge-DWINT is driven by repulsive interactions for ionic strengths lower than 10-2 mol.L-1. By contrast, higher salt concentrations lead to attractive interactions that destabilize the colloid suspension, inducing nanotube coagulation into larger structures that settle over time or form opaque gels. Detailed simulations of the WAXS diagram reveal that aggregates are mainly formed by an isotropic distribution of small bundles (less than 4 nanotubes) in which the nanotubes organized themselves in parallel orientation. Altogether, these measurements allow us to give the first overview of the phase diagram of colloidal dispersions based on geo-inspired imogolite-like nanotubes.

International audience; Metal oxide aluminosilicate and aluminogermanate nanotubes, called imogolite nanotubes, are custom made nanotubes with controlled diameter, morphology and organization. These nanotubes undergo major structural changes at high temperatures. Here, we report a complete analysis of the structural transformation of single and double-walled aluminogermanate nanotubes, organized or not in bundles, up to 800 • C. Complementary X-ray scattering and spectroscopy experiments were performed. The evolution of both Al and Ge atoms coordination during the transformation process was studied in-situ. Quantitative analysis of X-ray absorption spectra reveals that the dehydroxylation of nanotubes leads to intermediate stages of 'metaimogolite', which differ in the coordination of the aluminium atoms. A mechanism explaining the major structural reorganization is proposed based on atomic jump processes.

International audience; Imogolite nanotubes display a range of useful properties and provide an ideal material system to study the assembly of nanomaterials into macroscopic fibers. A method of wet spinning pure, binder-free imogolite fibers has been developed using double-walled germanium imogolite nanotubes. Nanotube aspect ratio can be controlled during the initial synthesis and is critical to the spinning process. Fibers made from short nanotubes (

Hypothesis Synthetic imogolite nanotubes form stable colloidal dispersions that may also exhibit a rich liquid-crystalline phase behavior according to the nanotube length to diameter ratio. Anisometric double-walled aluminogermanate nanotubes are now readily available through hydrothermal treatment of germanium and aluminum precursors. This work aims to assess how the self-organization behavior of these nanotubes is influenced by the nature of the precursors. Experiments Five different samples were synthesized by changing the precursors involved in the formation of either inner or outer walls, then fully characterized. From series of aqueous dispersions prepared by osmotic stress, we evaluated the phase behavior by coupling polarized optical observations and small-angle X-ray scattering. Findings The formation of anisometric nanotubes is achieved whatever the initial conditions. Their structural properties are however affected by the nature of the aluminum salt. For nanotubes synthesized with aluminum perchlorate, the dispersions present an isotropic-to-columnar phase transition with a self-organization of the nanotubes over large distances. By contrast, nanotubes synthesized with chloride and nitrate salts form only nematic or isotropic liquids and tend to group together in bi-dimensional rafts. We suggest that the different phase behaviors are related at the first order to the presence of structural vacancies in the nanotube walls.

The assembly of one-dimensional nanomaterials into macroscopic fibers can improve mechanical as well as multifunctional performance. Double-walled aluminogermanate imogolite nanotubes are geo-inspired analogues of carbon nanotubes, synthesized at low temperature, with complementary properties. Here, continuous imogolite-based fibers are wet-spun within a poly(vinyl alcohol) matrix. The lyotropic liquid crystallinity of the system produces highly aligned fibers with tensile stiffness and strength up to 24.1 GPa (14.1 N tex–1) and 0.8 GPa (0.46 N tex–1), respectively. Significant enhancements over the pure polymer control are quantitatively attributed to both matrix refinement and direct nanoscale reinforcement, by fitting an analytical model. Most intriguingly, imogolite-based fibers show a high degree of healability via evaporation-induced self-assembly, recovering up to 44% and 19% of the original fiber tensile stiffness and strength, respectively. This recovery at high absolute strength highlights a general strategy for the development of high-performance healable fibers relevant to composite structures and other applications.

X-ray scattering (XRS) experiments have been performed on multi-layered graphene oxide (GO) paper. GO can be easily hydrated as water naturally intercalates in the hydro­philic nanostructure. The effect of the intercalated water on the XRS signals is measured during dehydration under thermal treatment in the temperature range 298–473 K as well as during hydration under saturated water vapour pressure. A simple modelling of the XRS signals by taking into account the presence and the type of intercalated water (bound water or physisorbed water) is introduced. It allows an explanation of the variations of intensity and position of XRS reflections observed experimentally., EP, SR and PL benefited of a grant from the French Research National Agency under the program Investissements d’Avenir (SEDECO project, ANR-10-LABX-0035: Labex NanoSa-clay). AMB and WKM acknowledge funding from the Spanish Ministry MINECO under projects ENE2013-48816-C5-5-R and ENE2016-79282-C5-1-R with their associated European Regional Development Funds, and from the Government of Aragon under Consolidated Group programme DGA-T66-GCNN and the associated European Social Fund.

6 Figuras, Owing to their great interest for energy storage and sensing applications, multi-layer papers consisting of graphene oxide – carbon nanotube (GO-CNT) hybrid sheets were prepared by in-situ exfoliation of graphite oxide in the presence of oxidized CNTs (oCNTs). For the first time we elucidate the influence of oCNTs on chemisorbed water (CW), i.e. water molecules inherently bound to oxygen functional groups (OFGs) of graphene oxide (GO) and responsible for irreversible structural damage upon thermal reduction processes. We show that oCNTs self-assemble onto GO sheets during the liquid phase processing steps by forming cooperatively strengthened OH···O=C hydrogen bonds between the carboxylic groups of oCNTs and OFGs of GO. At oCNT contents of about 10 to 15 wt. % this leads to the displacement of considerable amounts of CW without altering the original chemical composition of GO. Thermally reduced GO-CNT (rGO-CNT) papers reveal improved sp2 character and an enhancement of the specific capacitance by 75% with respect to thermally reduced GO (rGO), largely due to the effective removal of CW by oxidized CNTs. These findings disclose the relevance of cooperative hydrogen bonding phenomena in graphene oxide paper/film electrodes for the development of improved electrochemical energy storage and sensing devices., JDN is thankful for his CSIC PhD grant JAEPre09-01155 covering also his research stay at Rice University. WKM and AMB acknowledge financial support from Spanish MINECO and the European Regional Development Fund through project grants ENE2013-48816-C5-5-R, ENE2016-79282-C5-1-R and the Government of Aragon and the European Social Fund under project DGA-FSE-T66 CNN. RA gratefully acknowledges the support from MINECO through project grants FIS2013-46159- C3-3-P and MAT2016-79776-P. Some of the research has received funding from the European Union FP7 program under Grant Agreement 312483 ESTEEM2 (Integrated Infrastructure Initiative – I3) and from the European Union H2020 program under the grant 696656 Graphene Flagship, and H2020 Marie Skłodowska-Curie grant 642742.

The role of the preferential orientation of clay platelets on the properties of a wide range of natural and engineered clay-rich media is well established. However, a reference function for describing the orientation of clay platelets in these different materials is still lacking. Here, we conducted a systematic study on a large panel of laboratory-made samples, including different clay types or preparation methods. By analyzing the orientation distribution functions obtained by X-ray scattering, we identified a unique signature for the preferred orientation of clay platelets and determined an associated reference orientation function using the maximum-entropy method. This new orientation distribution function is validated for a large set of engineered clay materials and for representative natural clay-rich rocks. This reference function has many potential applications where consideration of preferred orientation is required, including better long-term prediction of water and solute transfer or improved designs for new generations of innovative materials., A reference function for describing the orientation of clay platelets in clay-rich materials is still lacking, but is necessary for applications such as prediction of water and solute transfer and designs of innovative materials. Here, the authors determine a reference orientation function of clay platelets, and validate their function for both engineered and natural clay-rich media.

International audience; Hollow cylinders with a diameter in the nanometer range are carving out prime positions in nanoscience. Thanks to their physico-chemical properties, they could be key elements for next-generation nanofluidics devices, for selective molecular sieving, energy conversion or as catalytic nanoreactors. Several difficult problems such as fine diameter and interface control are solved for imogolite nanotubes. This chapter will present an overview of this unique class of clay nanotubes, from their geological occurrence to their synthesis and their applications. In particular, emphasis will be put on providing an up-to-date description of their structure and properties, their synthesis and the strategies developed to modify their interfaces in a controlled manner. Developments on their applications, in particular for polymer/imogolite nanotubes composites, molecular confinement or catalysis, are presented.

International audience

Kaolinite and its dehydroxylated forms are widely used in industry, including the growing field of geopolymers. Until now, a deep understanding of the dissolution mechanism of kaolinite particles in alkaline media is still lacking. This work aims to investigate the dissolution mechanisms through aluminum and silicon leaching of two references kaolinites (KGa-1b and KGa-2) regarding various 2 M alkali treatment (KOH, NaOH and 50/50 NaOH + KOH) as a function of time and at 80 °C. For this, a wide range of methods have been used, from the determination of [Si] and [Al] in solution to the analysis of solids by combining X-ray diffraction (XRD), Fourier Transformed Infrared (FTIR), X-ray Absorption Near Edge Structure (XANES) and Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) spectroscopies and Transmission Electronic Microscopy (TEM) observations. The results evidence a higher dissolution rate with poorly crystallized kaolinites, confirming the role of the crystallinity of the samples toward reactivity in an alkaline media. In addition, the nature of the cation significantly affect the degree of dissolution following the sequence KOH

This article presents the technical characteristics of a newly built small- and wide-angle X-ray scattering (SAXS/WAXS) apparatus dedicated to structural characterization of a wide range of nanomaterials in the powder or dispersion form. The instrument is based on a high-flux rotating anode generator with a molybdenum target, enabling the assessment of highly absorbing samples containing heavy elements. The SAXS part is composed of a collimation system including a multilayer optic and scatterless slits, a motorized sample holder, a vacuum chamber, and a two-dimensional image-plate detector. All the control command is done through a TANGO interface. Normalization and data correction yield scattering patterns at the absolute scale automatically with a q range from 0.03 to 3.2 Å−1. The WAXS part features a multilayer collimating optic and a two-dimensional image-plate detector with variable sample-to-detector distances. The accessible q range is 0.4–9 Å−1, ensuring a large overlap in q range between the two instruments. A few examples of applications are also presented, namely coupled SAXS/WAXS structure and symmetry determination of gold nanocrystals in solution and characterization of imogolite nanotubes and iron-filled carbon nanotube samples.

International audience; A groundbreaking discovery in nanofluidics was the observation of the tremendously enhanced water permeability of carbon nanotubes, those iconic objects of nanosciences. The origin of this phenomenon is still a subject of controversy. One of the proposed explanations involves dramatic modifications of the H-bond network of nanoconfined water with respect to that of bulk water. Infrared spectroscopy is an ideal technique to follow modifications of this network through the inter- and intramolecular bonds of water molecules. Here we report the first infrared study of water uptake at controlled vapor pressure in single walled carbon nanotubes with diameters ranging from 0.7 to 2.1 nm. It reveals a predominant contribution of loose H bonds even for fully hydrated states, irrespective of the nanotube size. Our results show that, while the dominating loosely bond signature is attributed to a one-dimensional chain structure for small diameter nanotubes, this feature also results from a water layer with “free” OH (dangling) bonds facing the nanotube wall for larger diameter nanotubes. These experimental findings provide a solid reference for further modeling of water behavior in hydrophobic nanochannels.

Synthetic imogolite-like nanotubes (INT) with well-defined diameters represent a considerable opportunity for the development of advanced functional materials. Recent progress has made it possible to increase their aspect ratio and unique self-organization properties were evidenced. We suggest that slight modification of the synthesis conditions may drastically affect the resulting liquid-crystalline properties. In this work, we investigate how the precursor&rsquo, s [Al]/[Ge] molar ratio (R&rsquo, ) impacts the morphology and the colloidal properties of aluminogermanate INTs by combining a multi-scale characterization. While only double-walled nanotubes are found for R&rsquo, &ge, 1.8, the presence of single-walled nanotubes occurs when the ratio is lowered. Except for the lowest R&rsquo, ratio investigated (R&rsquo, = 0.66), all synthetic products present one-dimensional shapes with a high aspect ratio. Small-angle X-ray scattering experiments allow us to comprehensively investigate the colloidal properties of the final products. Our results reveal that a liquid-crystalline hexagonal columnar phase is detected down to R&rsquo, = 1.33 and that it turns into a nematic arrested phase for R&rsquo, = 0.90. These results could be useful for the development of novel stimuli-responsive nanocomposites based-on synthetic imogolite nanotubes.

© 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, Hydration of a multi-layered graphene oxide (GO) paper in water vapor atmosphere was studied by in-situ X-ray scattering over a wide range of relative humidity (RH). The intercalation of water molecules physically adsorbed between GO layers induces the expansion of the interlayer distance. Two regimes of adsorption are clearly evidenced according to the variation of the interlayer distance as a function of the relative humidity. The expansion of the interlayer distance is limited to ∼1 Å for RH ranging from 6 to 53%, whereas it is ∼3.5 Å for RH 75–100%. The hydration mechanism corresponds to the progressive adsorption of water molecules onto hydrophilic sites at the surface of GO layers in the low-RH regime, then an additional water monolayer is formed in the high-RH regime., EP, SR and PL benefited of a grant from the French Research National Agency under the program Investissements d’Avenir (SEDECO project, ANR-10-LABX-0035: Labex NanoSaclay). AMB and WKM acknowledge funding from the Spanish MINEICO (project ENE2016-79282-C5-1-R), the Gobierno de Aragón (Grupo Reconocido TO3_17R) and associated EU Regional Development Funds.

Le meme formalisme est utilise pour expliquer la diffraction par l’ADN et par les nanotubes de carbone ou leurs analogues d’oxydes metalliques, les nanotubes d’imogolite.La diffraction permet a la fois de determiner la structure et l’organisation des nanotubes. De la diffraction electronique a celle des rayons X, nous discutons des proprietes individuelles et d’ensemble de ces nanostructures.

International audience; New developments in nanosciences and nanotechnologies are strongly dependent on our ability to synthesize well-controlled nanobuilding units, with specific properties. We report in this paper the first synthesis of hybrid single-walled imogolite nanotubes (OH)3Al2O3SixGe1?xCH3 with diameter-controlled hydrophobic nanopores varying from 1.8 to 2.4 nm. Methylation and nanotube dimensions are studied by combining infrared spectroscopy, cryo-TEM observations, and X-ray scattering measurements. We show that, in solution, the water density inside methylated nanotubes is decreased by a factor of 3 compared to the bulk value. Spontaneous confinement of bromopropanol molecules inside the nanotubes, when added to the solution, is demonstrated. These newly synthesized nanotubes may open up possibilities for water filtration or water decontamination.

International audience; Significant developments have been proposed over the last decade in the synthesis of aluminosilicate and aluminogermanate imogolite-like nanotubes. But while liquid phase synthesis is well controlled, it is not the case for imogolite or imogolite-like nanotube arrangement in dry state. In particular, nanotubes are found to self-assemble in bundles of various sizes, which may impact the properties of the final product. Here, we investigate the effect of ionic strength on bundling of aluminogermanate single-walled imogolite nanotubes (Ge-SWINT) in aqueous suspensions and in the resulting powders after solvent evaporation. The nanotube arrangement as a function of salt concentration was studied by X-ray scattering experiments and simulations. In aqueous suspension, nanotubes bundling occurs only at high ionic strength (IS > 8 × 10$^{-2}$ mol.L$^{-1}$) while beyond this threshold, the increase of electrostatic repulsions induces a complete stabilization of individual nanotubes. After solvent evaporation, nanotube arrangement is shown to be dictated principally by the initial concentration of salt. Beyond an ionic strength of ~ 10$^{-3}$ mol.L$^{-1}$ in the starting suspension, all Ge-SWINT samples tend to form large bundles in powder, whose lattice parameter are independent of the initial salt concentrations. These experimental results clearly show that the positive surface charge of imogolite can be used to control nanotubes bundling by anion condensation.

International audience

Liquid crystals have found wide applications in many fields ranging from detergents to information displays and they are also increasingly being used in the ‘bottom-up' self-assembly approach of material nano-structuration. Moreover, liquid-crystalline organizations are frequently observed by biologists. Here we show that one of the four major lyotropic liquid-crystal phases, the columnar one, is much more stable on dilution than reported so far in literature. Indeed, aqueous suspensions of imogolite nanotubes, at low ionic strength, display the columnar liquid-crystal phase at volume fractions as low as ∼0.2%. Consequently, due to its low visco-elasticity, this columnar phase is easily aligned in an alternating current electric field, in contrast with usual columnar liquid-crystal phases. These findings should have important implications for the statistical physics of the suspensions of charged rods and could also be exploited in materials science to prepare ordered nanocomposites and in biophysics to better understand solutions of rod-like biopolymers., Liquid crystals are grouped into four main classes—nematic, lamellar, cubic and columnar—depending on their symmetries. Here, the authors show for the first time that a columnar phase can form in suspensions of imogolite nanotubes at very low concentrations.

Imogolites, which are aluminosilicate or aluminogermanate nanotubes, are usually known as cylindrical nanotubes. However, in powders, deformations or further structural modifications of these nanotubes occur due to intertube interactions or under the action of temperature. Depending on whether they are organised in bundles or not, ovalisation or hexagonalisation phenomena are reported, based on detailed X-ray scattering (XRS) studies. The basics of XRS and the specific models developed for investigating such structural modifications are presented. Finally, thermally induced structural transformations, from the dehydroxylation process to the lamellar and high-temperature mullite phases, are reviewed.

We illustrate the contribution of inelastic neutron scattering to the understanding of the vibrations and lattice excitations of fullerenes and carbon nanotubes, through some significant experimental results. Particular emphasis is placed on the study of intra and inter-molecular modes of fullerene C60, as well as on the order/disorder transition characteristic of these molecules. In addition, a significant part of this article is dedicated to various intercalation compounds of fullerenes and carbon nanotubes, such as the co-crystal “fullerene-cubane” consisting of an arrangement of molecules of spherical and cubic shapes, or the compound called “peapods”, in which fullerene C60 are inserted inside carbon nanotubes.

We present results of Monte Carlo simulations of chains of C-60 and chains of C-70 molecules encapsulated in a single-walled carbon nanotube (SWCNT). We observe the changes in the configuration of the fullerene molecules when varying tube radius and temperature. In particular, the evolution of the pair correlation functions reveal a transition from linear harmonic chain behavior to a hard-sphere liquid upon heating, demonstrating the possibility of tuning properties of C-60- and C-70@SWCNT peapods with radius and temperature.

Fullerenes inserted in single-walled carbon nanotubes, the so-called “peapods,” provide scientists with an exceptional molecular model system to study one-dimensional physics and confinement. In this communication, we present recent inelastic neutron scattering measurements concerning the translational dynamics of this one-dimensional system. The recent synthesis of a large amount of two-dimensional oriented samples allows us to extract the sole contribution of the inserted C60 chains. The related quasi-elastic-like peak evolves with the temperature but never shows an additional inelastic contribution when lowering temperature, indicating that carbon peapod is a true one-dimensional system down to low temperatures.

We present Monte Carlo simulations of chains of C70 molecules encapsulated in a single-walled carbon nanotube (SWCNT). For various tube radii R (6.5 Å less-than-or-equals, slant R less-than-or-equals, slant 7.5 Å), we analyze rotational and translational motion of the C70 molecules, as a function of temperature. Apart from reproducing the experimentally well-established lying and standing molecular orientations for small and large tube radii, respectively, we observe, depending on the tube diameter, a variety of molecular motions, orientational flipping of lying molecules, and the migration of molecules resulting in a continual rearrangement of the C70 molecules in clusters of varying lengths. With increasing temperature, the evolution of the pair correlation functions reveals a transition from linear harmonic chain behavior to a hard-sphere liquid, making C70@SWCNT peapods tunable physical realizations of two well-known one-dimensional model systems.

The single-walled carbon nanotubes (SWCNTs) were synthesized by the carbon monoxide disproportionation reaction on Fe catalyst particles formed by ferrocene vapor decomposition in a laminar flow aerosol (floating catalyst) reactor. On the basis of in situ sampling of the product collected at different locations in the reactor, kinetics of the SWCNT growth and catalyst particle crystallinity were studied. Catalyst particles captured before SWCNT nucleation as well as inactive particles were determined to have cementite (Fe3C) phase, while particles with γ- and α-Fe phases were found to be embedded in the SCWNTs. The growth rate in the temperature range from 804 to 915 °C was respectively varied from 0.67 to 2.7 μm/s. The growth rate constant can be described by an Arrhenius dependence with an activation energy of Ea = 1.39 eV, which was attributed to the carbon diffusion in solid iron particles. CNT growth termination was explained by solid–liquid phase transition in the catalyst particles. A high temperature gradient in the reactor was found to not have any effect on the diameter during the SWCNT growth and as a result on the chirality of the growing SWCNTs.

The true chemical nature and physical state of the catalyst particles in Catalytic Chemical Vapor Deposition (CCVD) synthesis of carbon nanotubes are the subject of intense discussions, as it is one of the keys to understand their growth mechanisms. The CCVD method considered in this article involves pyrolysis of mixed liquid aerosols and leads to the synthesis of large carpets of multiwalled nanotubes (MWNTs) partially filled with iron-based materials. The experimental approach consists in studying the influence of the cooling procedure applied at the end of the synthesis. Both slow standard cooling or quenching were performed, and the structure and chemical state of the iron-based particles were compared through complementary local and global investigations involving X-ray diffraction, electron microscopy, electron diffraction, as well as electron energy loss spectroscopy. We clearly demonstrate that iron-based catalyst particles are carbon-rich and oxygen-free in quenched samples, and that they oxidize during the slow cooling step. It is inferred that they are very probably molten supersaturated carbon-metal particles during the NT growth.

International audience; Abstract Catalytic Chemical Vapor Deposition is the most promising process to obtain Vertically Aligned Carbon Nanotube (VACNT) carpets. Live analysis of growing VACNT is crucial to reveal their nucleation and growth mechanisms. We present novel time resolved in situ X-ray diffraction (XRD) analysis on growing macroscopic VACNT carpets enabling us to get statistical information on catalytic phase together with nanotube progressive alignment. A specific synthesis set-up has been developed to perform such in situ synchrotron XRD experiments. Nucleation kinetics of the different phases are evidenced: first, orthorhombic Fe3C crystalline phase is formed, followed by the formation of CNTs and finally of γ-Fe, demonstrating that Fe3C particles are the nucleation seeds for CNT growth. The additional formation of Fe3C or γ-Fe nanowires inside CNTs is associated with capillary forces and mobility of them at 850°C. Experiments also reveal the progressive formation and alignment of VACNT carpets during the continuous precursor injection. Quantification of the alignment degree allows one to get a better understanding of the effect of precursor injection rate and CNT length on VACNT alignment. The overall results are key issues for the scaling-up of VACNT synthesis and their applications towards commercialization.

In this review we present three representative examples of molecular disorder: substitution disorder for carbon nanotubes in zeolite, coupling between substitution disorder and displacements through the pinning of charge-density waves in one-dimensional molecular conductors, and the combination of random packing with orientational disorder in the C60—C60 dimers systems.

We report the fabrication process of isolated one-dimensional Se chains incorporated in the matrix of AlPO4-5 single crystals and the experimental investigation of the geometry, phase stability, electronic properties, and electron-phonon coupling effect of these Se chains. The structure of the helical Se chains inside the channels is discussed on the basis of X-ray scattering measurements. Thermal analysis and temperature-dependent micro-Raman measurements show that Se single chains are flexible and can convert from a weak distorted phase into another phase with strongly disordered structure ("melting" state) around 340 K. Since the electrons are confined in the one-dimensional channels, the absorption band of the Se chain is obviously blue shifted compared with that of trigonal Se. With increasing temperature, this band shifts linearly to the lower energy side, in sharp contrast to the nonlinear temperature coefficient of trigonal Se, which is attributed to the greatly diminished interchain interaction and the weakening of the electron-optical phonon coupling in a low-dimensional system. In the vicinity of the absorption band, both first-order and second-order Raman signals for the Se chain are enhanced, due to the strong electron-phonon coupling when the excitation laser energy matches the electronic transition in isolated Se chains.

We report structure-property correlations in single-wall carbon nanotube (SWNT) fibers, among electrical, thermal, and chemical parameters with respect to stretch-induced preferential SWNT alignment along the fiber axis. Purified HiPco (high-pressure CO) conversion tubes are dispersed with the aid of an anionic surfactant and coagulated in the co-flowing stream of an adsorbing polymer. The fibers are then dried, rewetted under tensile load, and redried to improve the alignment. Complete removal of the polymer was assured by annealing in hydrogen at 1000°C. The degree of alignment was determined by x-ray scattering from individual fibers using a two-dimensional detector. The half width at half maximum describing the axially symmetric distribution of SWNT axes decreases linearly from 27.5° in the initial extruded fiber to 14.5° after stretching by 80%. The electrical resistivity ρ at 300K decreases overall by a factor ∼4 with stretching, for both as-spun composite and polymer-free annealed fibers. However, ...

We present detailed calculations of the diffraction pattern of a powder of bundles of C$_{60}$ peapods. The influence of all pertinent structural parameters of the bundles on the diffraction diagram is discussed, which should lead to a better interpretation of X-ray and neutron diffraction diagrams. We illustrate our formalism for X-ray scattering experiments performed on peapod samples synthesized from 2 different technics, which present different structural parameters. We propose and test different criteria to solve the difficult problem of the filling rate determination.

Detailed synthesis process of selenium species incorporated in the channels of AlPO 4 -5 zeolite single crystals is reported X-ray scattering experiments show diffuse planes which can be analyzed in terms of a partial filling of the channels by helical selenium chains. Polarized Raman and polarized absorption spectra confirm that the helical chains are highly aligned along the channel direction, while the rings appear randomly distributed in the channels. The helical chains have a lowest optical absorption band at 2.6 eV that is strongly polarization dependent, while the rings have a lowest absorption band at 3.0 eV that varies slowly with the light polarization. 2003 Flsevier B.V. All rights reserved.

The diameter distribution of the nanotubes produced by electric-arc discharge are measured using Raman spectroscopy at various wavelengths. These measurements agree with the results provided by two other techniques: high-resolution transmission electron microscopy and x-ray diffraction. The mean tube diameter shifts more than 0.1 nm with the increase of argon in the inert atmosphere. Some argon concentrations favored the synthesis of metallic tubes with specific diameters. Furthermore, the background gas influences the macroscopic characteristics of nanotube yield and bundle size, as determined by Brunauer–Emmett–Teller surface area measurements and x-ray diffraction. The information collected on nanotube diameter and arrangement is correlated with temperatures calculated using a numerical model of the plasma generated between the two electrodes. Indeed, plasma temperature control during the production process is achieved using argon–helium mixtures as buffer gases. The variation of the gas mixture from pure argon to pure helium changes the plasma temperature and hence the nanotube diameter.

We report the first X-ray diffraction and Raman spectroscopy study of a single crystal of the rare-earth endohedral fullerene Dy@C82. The lattice is found to be body-centered cubic (a = 25.79 A, space group $I\bar {4}3d)$ which is at variance with previous reports and confirms that several types of structures can be stabilized in Dy@C82. X-ray diffraction/diffuse scattering methods reveal no low-temperature change down to 12 K for the present structure. The Raman spectroscopy data are comparable to those of other M@C82 endohedral compounds. However, the Dy oxidation state and the force constant of the low-frequency metal-cage stretching mode do not follow the simple relationship observed before.