Jean-Louis Bantignies

Wettability contrasts in kaolinite and illite clays; characterization by infrared and X-ray absorption spectroscopies

A reservoir rock is a porous geological formation in contact with 2 liquids, brine and oil. An improved knowledge of rock wettability is of primary importance to estimate the amount of crude oil in underground resources. The petroleum industries have observed that wettability contrasts in sedimentary reservoir rocks are largely correlated to the presence of clays, illite and/or kaolinite in the rocks’ intergranular space.More precisely, the grain surfaces of illite show a preference for brine. Kaolinite preferentially adsorbs oil, which imparts its hydrophobic characteristics to the mineral surface. Using X-ray absorption spectroscopy (XAS) and Fourier transform infrared (FTIR) spectroscopy, we studied the adsorption process of asphaltenes in the presence of water at the microscopic level. We demonstrate experimentally that the wettability contrasts observed in kaolinite and illite are related to structural differences between these 2 clays, and we show the role of the grain surface hydroxyls. With clay materials, the purity of the samples is the most important limitation of the quantitative use of extended X-ray absorption fine structure (EXAFS).

Eu3+-Based Bridged Silsesquioxanes for Transparent Luminescent Solar Concentrators

The sol-gel preparation of a bridged silsesquioxane containing europium(III) salts and 2-thenoyltrifluoroacetone has been achieved from a new ethane tetracarboxamide-based organosilane. Free-standing films with thicknesses up to 440 μm and maximum absolute quantum yield (q) of 0.34 ± 0.03 (excitation at 320 nm) were prepared by the drop cast method, while thin films (∼200-400 nm) spin-coated on glass substrates led to highly luminescent coatings with q = 0.60 ± 0.02 (excitation at 345 nm). The thin films were tested as planar luminescent solar concentrators and the optimized device displays an optical conversion efficiency of 12.3% in the absorbing spectral region of the active layer (300-380 nm).

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.

Self-assembly of bridged silsesquioxanes: modulating structural evolution via cooperative covalent and noncovalent interactions.

The self-assembly of a bis-urea phenylene-bridged silsesquioxane precursor during sol-gel synthesis has been investigated by in situ infrared spectroscopy, optical microscopy, and light scattering. In particular, the evolution of the system as a function of processing time was correlated with covalent interactions associated with increasing polycondensation and noncovalent interactions such as hydrogen bonding. A comprehensive mechanism based on the hydrolysis of the phenylene-bridged organosilane precursor prior to the crystallization of the corresponding bridged silsesquioxane via H-bonding and subsequent irreversible polycondensation is proposed.

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.

Turning Peptide Sequences into Ribbon Foldamers by a Straightforward Multicyclization Reaction

The conformational control of molecular scaffolds allows the display of functional groups in defined spatial arrangement. This is of considerable interest for developing fundamental and applied systems in both the fields of biology and material sciences. Peptides afford a large diversity of functional groups, and peptide synthetic routes are very attractive and accessible. However, most short peptides do not possess well-defined secondary structures. Herein, we developed a simple strategy for converting peptide sequences into structured γ-lactam-containing oligomers while keeping the amino acids side chain diversity. We showed the propensity of these molecules to adopt ribbon-like secondary structures. The periodic distribution of the functional groups on both sides of the ribbon plane is encoded by the initial peptide sequence.

THE TRAPPING OF B FROM WATER BY EXFOLIATED AND FUNCTIONALIZED VERMICULITE

Micron-grade natural vermiculite was modified by several physical and chemical treatments in order to increase the adsorption capacity of this material for B. A thermal exfoliation (T = 600°C) of pristine material, a chemical exfoliation through reaction with hydrogen peroxide (H2O2 35%), or grafting of a specific B complexant (i.e. N-methyl-D-glucamine: NMDG) led to an increase in the uptake of B at low initial concentrations of the aqueous solutions ([B] ≈ 5 mg L−1). The more efficient material is the NMDG-grafted clay, for which the adsorption uptake is four times greater than that of raw vermiculite, and reaches 0.04 mmol g−1. For all modified materials, the effect of the pH on B adsorption and the adsorption kinetics were studied and compared to raw vermiculite. Adsorption isotherms were also plotted and fitted well with the Freundlich equation.

Origin of Invariant Gel Melting Temperatures in the c-T Phase Diagram of an Organogel.

Binary c-T phase diagrams of organogelators in solvent are frequently simplified to two domains, gel and sol, even when the melting temperatures display two distinct regimes, an increase with T and a plateau. Herein, the c-T phase diagram of an organogelator in solvent is elucidated by rheology, DSC, optical microscopy, and transmitted light intensity measurements. We evidence a miscibility gap between the organogelator and the solvent above a threshold concentration, cL. In this domain the melting or the formation of the gel becomes a monotectic transformation, which explains why the corresponding temperatures are nonvariant above cL. As shown by further studies by variable temperature FTIR and NMR, different types of H-bonds drive both the liquid-liquid phase separation and the gelation.