Philippe Dieudonné

One‐Pot Construction of Multipodal Hybrid Periodic Mesoporous Organosilica Nanoparticles with Crystal‐Like Architectures

The design of hybrid multipodal PMO (mp-PMO) nanoparticles with crystal-like architectures elaborated in a one-pot, two-step process, involving the preparation of a benzene-based spherical PMO core followed by the formation of ethylene-based rod-shaped PMO pods on these cores is described.

Toward organization of cyano-bridged coordination polymer nanoparticles within an ionic liquid crystal.

Size controlled cyano-bridged coordination polymer nanoparticles Mn1.5[Cr(CN)6] have been synthesized and organized at the nanolevel by using the room temperature ionic liquid crystal (ILC) C12-MIMBF4. The as-obtained material was studied by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), optical microscopy, and X-ray diffraction. These analyses reveal the presence of a long-range organization of cyano-bridged nanoparticles at the nanoscale level within the ILC phase. The magnetic study of these nanoparticles reveals an appearance of a nanocluster-glass-like regime caused by magnetostatic interactions between neighboring nanoparticles. The properties of these organized nanoparticles have been compared with the properties of nanoparticles of the same composition and stoichiometry obtained and randomly dispersed into the isotropic IL C10-MIMBF4.

Two fractal structures in aerogel

Abstract Composite aerogels have been prepared by the addition of silica soot (aerosil) in the solution before gelation. The fractal network previously described which results from the aggregation mechanism of the organosiloxane is strongly affected by the influence of the aerosil soot. Ultra small angle X-ray scattering measurements at ESRF show that besides the fractal network built up by the organosiloxane, the silica soot is forming another fractal structure at a higher scale. The fractal dimension characterizing the inorganic network could be interpreted as the signature of the linkage between the polymeric clusters. From a mechanical point of view, for aerosil content lower than 40 wt% , the elastic modulus is not dependent on the aerosil fractal network and the mechanical features are those of the polymeric gel.

Organosilicas based on purine–pyrimidinebase pair assemblies: a solid state NMR point of view

Organosilicas based on adenine (A) and thymine (T) assemblies have been synthesized. A surfactant-free route, based on specific molecular recognition between A and T entities, has been developed. The characterization of the H-bond networks, in both homo- and hetero-assemblies, has been emphasized by using 1H solid state NMR (nuclear magnetic resonance). The latest experimental developments were implemented (i.e. very fast MAS (magic angle spinning) experiments at 750 MHz and 33 kHz), in order to enhance drastically the spectral resolution. Moreover, 1H experiments at 67 kHz in 1.3 mm rotors were performed. Spatial connectivities between protons were established by using 1H–1H DQ (double quantum) MAS experiments, allowing the precise characterization of A/A, T/T and A/T associations.

Structural ordering of self-assembled alkylene-bridged silsesquioxanes probed by X-ray diffraction experiments

Powder X-ray diffraction experiments have been performed to analyse the structural order in alkylene bridged silsesquioxanes. These organic–inorganic hybrids were obtained by the hydrolysis–condensation of a series of six α,ω-bis[triethoxysilyl(propyl)ureido]alkylenes associating hydrophobic alkylene units with various chain length and H-bonding urea groups. The sol–gel hydrolysis in ethanol with a stoichiometric amount of water and using fluoride anion as catalyst only afforded amorphous bridged silsesquioxanes. Conversely, the hydrolysis with a large excess of water under acidic catalysis produced materials as layered sheets. A lamellar periodicity on the molecular scale level was observed for longer alkylene chain (Cn C8–C12). Under similar reaction conditions, the hydrolysis of the short alkylene chain precursor (C6) led to an amorphous solid. The medium to long range arrangement of the organic fragment in the solids is attributable to a combination of the hydrogen bonding interactions between the urea groups and of the van der Waals interactions between the long alkylene chains. In excess water, the hydrophobic nature of the long alkylene chains prevails and favours the formation of the intermolecular H-bonds between the urea groups leading to ordered assemblies of the organic substructures in the silsesquioxane network.

In situ X-ray measurements to probe a new solid-state polycondensation mechanism for the design of supramolecular organo-bridged silsesquioxanes.

A long-range ordered organic/inorganic material is synthesized from a bis-silane, (EtO)(3)Si-(CH(2))(3)-NHCONH-C(6)H(4)-NHCONH-(CH(2))(3)-Si(OEt)(3). This crosslinked sol-gel solid exhibits a supramolecular organization via intermolecular hydrogen bonding interactions between urea groups (-NHCONH-) and covalent siloxane bonding, triple bond Si-O-Si triple bond. Time-resolved in situ X-ray measurements (coupling small- and wide-angle X-ray scattering techniques) are performed to follow the different steps involved in the synthetic process. A new mechanism based on the crystallization of the hydrolyzed species followed by their polycondensation in solid state is proposed.

Nanostructured assemblies from nucleotide-based amphiphiles

A synthetic route to 3′-O-alkyl nucleotides is described that provides easy access to a series of nucleotide-based amphiphiles. Physicochemical experiments demonstrate that these nucleotide amphiphiles possess different aggregating properties compared to both their non-nucleotide analogues and simple nucleotides. The data collected from TEM, SEM, FT-IR and WAXS studies indicate that the aqueous dispersion of these nucleotide amphiphiles provides nanostructured assemblies such as ribbon-like structures for the thymidine derivatives and small aggregates for adenine. These results indicate that the nature of the base has an impact on aggregate morphology. A molecular model illustrating the 3D supramolecular arrangements of a thymidine nucleoamphiphile forming ribbons is proposed.

Very large-scale structures in sintered silica aerogels as evidenced by atomic force microscopy and ultra-small angle X-ray scattering experiments

During the last few years the bulk structure of silica aerogels has been extensively studied mainly by scattering techniques (neutrons, X-rays, light). It has been shown that small silica particles aggregate to constitute a fractal network. Its spatial extension and fractal dimension are strongly dependent on the synthesis conditions (e.g., pH of gelifying solutions). These typical lengths range from 1 to 10 nm. Ultra-small angle X-ray scattering (USAXS) and atomic force microscopy (AFM) experiments have been carried out on aerogels at different steps of densification. The results presented in this paper reveal the existence of a spatial arrangement of the solid part at a very large length scale. The evolution of this very large-scale structure during the densification process has been studied and reveals a contraction of this macro-structure made of aggregates of clusters.

Nanostructuring of Hybrid Silicas through a Self‐Recognition Process

The hydrolysis and condensation of a silylated derivative of ureidopyrimidinone led to nanostructured hybrid silica, such as that depicted, as clearly shown by powder XRD studies. The nanostructuring was directly related to molecular recognition through hydrogen bonding. By combining FTIR, solution and solid-state NMR spectroscopic data, the transcription of the hydrogen-bonding networks from the precursor to the final product was clearly evidenced.

Formation of nanocomposites of platinum nanoparticles embedded into heavily fluorinated aniline and displaying long range organization

The synthesis of platinum nanoparticles organized inside rod or wire shaped superstructures is described. Such organization results from the combination of an organometallic route leading to size-controlled nanoparticles with the use of a fluorinated aniline able to self-assemble as a stabilizing agent. Several techniques were employed to characterize the nanomaterials obtained including TEM, HRTEM, WAXS, SEM-FEG and SAXS which confirmed the nanoparticle organization.