Pierre-Antoine Albouy

Shape-Controlled Platinum Nanocubes and Their Assembly into Two-Dimensional and Three-Dimensional Superlattices†

Liquid-liquid phase transfer has been used to synthesize platinum nanocrystals with a cubic morphology. By finely tuning the parameters controlling the nucleation and growth processes, nanometric truncated cubes or perfect cubes may be obtained. To our knowledge, this is the first time such shapes are obtained with this procedure. The importance of both the length of the capping agent to control the growth process and the bromide anions as poison for the (111) facet is shown. The low degree of size polydispersity allows these nanocrystals to self-assemble with a long-range ordering in two-dimensional and three-dimensional supracrystals. According to the nanocrystal shape, simple cubic or face-centered cubic supracrystals are observed. It is remarkable to notice that well-faceted supracrystals with sizes on the order of 10 microm may be obtained.

Recent structural investigations of metallic polymers

Abstract Recent structural studies of the undoped and iodine-doped polyacetylenes (prepared by the Tsukamoto and co-workers method), PF 6 − -doped polypyrrole and polyaniline emeraldine base and (hydrochloric acid and camphorsulfonic acid) salts are presented. Some key features of the polymer chain array and its evolution with the conditions of preparation are emphasized. Special attention has been devoted to characterization of the various sources of structural disorder in the relationship with high conductivity and related properties exhibited by these three families of polymers. Variation in the structural order in both crystalline and amorphous regions correlates directly with the electrical and optical properties of the metallic state.

Design of meso-structured titanium oxo based hybrid organic–inorganic networks

Titanium oxo clusters or nanosized Ti–O particles with hydrophobic or hydrophilic character can be obtained by varying the sol–gel synthesis conditions. These species are potentially interesting nano-building blocks (NBB) in the design of textured materials. The reactivity of well-defined hydrophobic NBB towards different nucleophiles has been characterised and discussed, in order to understand the processes taking place in the formation of meso-organised hybrids. Subsequently, different synthesis conditions were used to generate textured titania-based hybrid phases, using PEO-based surfactants as templating agents. The tuning of the interactions between the template and the different kinds of nano-building blocks allow worm-like and hexagonal titania-based hybrid phases to be reproducibly obtained.

Highly oriented 3D-hexagonal silica thinfilms produced with cetyltrimethylammonium bromide

Mesoporous silica thin films have been produced by sol–gel chemistry in the presence of cetyltrimethylammonium bromide (CTAB) template. The films were deposited on silicon or glass substrates by dip-coating and underwent different treatments to eliminate the CTAB and create porosity. As-prepared and treated coatings exhibit good optical quality. Their structures were fully characterised by transmission electron microscopy (TEM) performed on film cross-sections and by X-ray diffraction (XRD) in θ–2θ scan mode, as well as in transmission mode using two different scattering geometries. The films exhibit large and homogeneous domains organised in a 3D-hexagonal (P63/mmc) structure with the c axis normal to the surface throughout their whole thickness. Numerical analysis of the TEM pictures confirms the space group deduced from the XRD measurements. To our knowledge, these are the first reported thin films obtained by dip-coating in the presence of CTAB which show such extended and highly mono-oriented 3D-hexagonal (P63/mmc) domains. The film thickness, porosity and refractive index were evaluated by ellipsometry for the various treated films.

Amphiphilic liquid-crystal block copolymer nanofibers via RAFT-mediated dispersion polymerization

Well-defined, cholesteryl-based, amphiphilic block copolymer nanofibers have been obtained in a simple, one-pot, ethanol/water dispersion polymerization process using poly((meth)acrylic acid-co-(poly(ethylene glycol) (meth)acrylate) copolymers end-functionalized by a reactive trithiocarbonate end-group as macromolecular reversible addition–fragmentation chain transfer agents (macroRAFT agents). The resulting highly concentrated dispersions were analyzed by TEM (transmission electron microscopy), cryo-TEM, SAXS (small angle X-ray scattering) and SANS (small angle neutron scattering), which allowed the shape and size of the nanoobjects formed in situ to be fully characterized and which revealed moreover the presence of a smectic order in the hydrophobic cores. Due to this particular substructure, the nanofiber organization was observed over a broad composition range of the amphiphilic block copolymers.

Simultaneous Growths of Gold Colloidal Crystals

Natural systems give the route to design periodic arrangements with mesoscopic architecture using individual nanocrystals as building blocks forming colloidal crystals or supracrystals. The collective properties of such supracrystals are one of the main driving forces in materials research for the 21st century with potential applications in electronics or biomedical environments. Here we describe two simultaneous supracrystal growth processes from gold nanocrystal suspension, taking place in solution and at the air-liquid interface. Furthermore, the growth processes involve the crystallinity selection of nanocrystals and induce marked changes in the supracrystal mechanical properties.

A first insight in the mechanisms involved in the self-assembly of 2D-hexagonal templated SiO2 and TiO2 mesostructured films during dip-coating

Since mesoporous materials can be prepared by combining the sol-gel chemistry and the structuring effect of surfactants, they have attracted attention for application in various high technology fields. The present work deals with the analyses of the mechanisms involved in the formation of SiO2 and TiO2 highly organised 2D-hexagonal meso-structured films using Brij 58 as surfactant. The preparation of such films by dip-coating involves rapid evaporation which makes the different steps difficult to control. Simultaneous in-situ SAXS (synchrotron) and interferometry analyses have been performed to get a first understanding of the self-assembly process. SiO2 and TiO2 materials have a different chemical reactivity (kinetics and coordination aspects). However, we show that the mechanisms involved during dip-coating are quite similar : the self-assembly leading to the organised phase takes place at a final stage of the drying process, involves the formation of a disorganised intermediate phase and depends also on the presence of micellar interfaces in addition to film/air and film/substrate interfaces.

Crystallinity Segregation upon Selective Self-Assembling of Gold Colloidal Single Nanocrystals

Spontaneous separation of single from polycrystalline 5 nm gold nanocrystals (NCs) is observed in colloidal solution. This segregation takes place upon self-assembling of single crystalline NCs at the air-solvent interface and in precipitated superlattices. Polycrystalline NCs are observed to remain in the suspension. Transmission electron microscopy analysis of the size distribution of NCs issued from the different populations indicates that the NC size does not change from each other, excluding therefore any size segregation in this process. Using both low-frequency Raman scattering and X-ray diffraction provides reliable characterization of nanocrystallinity for each population of NCs, thus confirming the crystallinity segregation. The single crystalline NCs are found by electron diffraction to self-assemble into close-packed superlattices with long-range translational and orientational ordering, while polycrystalline NCs behave like spheres with no preferential orientation. The face-to-face orientational ordering, which is only observed for single crystalline NCs, supports the relevance of the specific crystallinity-related morphologies of these NCs in their better ability to self-assemble. Exploiting this spontaneous segregation would open up a simple alternative to other demanding routes for controlling crystallinity of nanocrystals and optimizing their properties for potential applications.

Tuning of Solid Phase in Supracrystals Made of Silver Nanocrystals

Decanethiol-passivated silver nanocrystals are shown, by small-angle X-ray diffraction, to organize into hexagonal close packed or face centered cubic (fcc) structures depending on the substrate temperature. When the nanocrystals are passivated by dodecanethiols, fcc and body centered cubic lattices as well as disordered arrangements are observed. The different crystalline phases correspond to thermodynamic equilibrium states. The passivant chain length is shown to control the interactions between the nanocrystals and consequently the superlattice structure.

Monolayer and multilayer assemblies of spherically and cubic-shaped iron oxide nanoparticles

Nowadays, nanoparticles are considered as the building blocks of the future nanotechnological devices and the development of strategies for processing nanoparticles into thin films has become a strategic challenge. In this context, the assembling of spherically shaped iron oxide nanoparticles displaying various sizes and of cubic-shaped nanoparticles has been investigated using the Langmuir–Blodgett technique. Homogeneous and dense monolayer and multilayer films have been obtained on large areas. The organisation in films has been studied by combining GISAXS and image analysis of SEM micrographs. The quality of the film has been determined to be mainly dependent on the chemical nature of the substrate and the amount of surfactant molecules at the surface of the nanoparticles (i.e. the organic coating).