Séverinne Rigolet

Pure silica chabazite molecular spring: a structural study on water intrusion-extrusion processes.

Water intrusion-extrusion isotherms performed at room temperature on hydrophobic pure silica chabazite show that the water-Si-CHA system displays real spring behavior. However, differences in pressure-volume diagrams are observed between the first and the other intrusion-extrusion cycles, indicating that some water molecules interact with the inorganic framework after the first intrusion. (29)Si and especially (1)H solid-state NMR showed the creation of new defect sites upon the intrusion-extrusion of water and the existence of two kinds of water molecules trapped in the supercage of Si-CHA: a first layer of water strongly hydrogen bonded with the silanols of the framework and a subsequent layer of liquidlike physisorbed water molecules undergoing interaction with the first layer. This hydrogen bonding scheme is also supported by X-ray powder diffraction.

Insights into photoinduced sol-gel polymerization: an in situ infrared spectroscopy study.

Photoacid-catalyzed sol-gel polymerization is now recognized as a powerful single-step synthetic approach to the synthesis of hybrid films, which can be distinguished from conventional sol-gel methods by higher reactivity and a solvent-free process. Despite its utility, the mechanism is not yet understood, in particular what chemical, physical, and photochemical parameters determine the precise sequence, kinetics, and advancement of this UV inorganic photopolymerization. Here, using mainly transmission real-time Fourier transformed infrared (RT-FTIR) spectroscopy, we characterize in situ the hydrolysis-condensation reactions of oligomeric silicon alkoxides and the formation of byproducts. Systematic review and assessment of numerous processing variables (relative humidity, film thickness, precursor structure, nature, and the concentration of photoacid generator) prove that the reaction kinetics are controlled by the two independent phenomena: the intrinsic chemical reaction rates and the water vapor permeation into the film.

Synthesis of purely silica MFI-type nanosheets for molecular decontamination

Conventional syntheses of zeolites generally lead to the formation of crystals whose sizes are of the order of several microns which is not detrimental in a large number of industrial applications. However, the capacity and kinetics of pollutant adsorption which are sensitive to diffusion phenomena, surface and porous volume could potentially be improved by the use of nanocrystal or hierarchical zeolites (micro/mesoporous or micro/macroporous). Indeed, zeosil nanosheets hold great potential because of their small size and their high porous volume that promote access of pollutants and increase the adsorption capacity. Herein, silicalite-1 zeosil with a lamellar morphology was successfully synthesized under hydrothermal conditions (110 °C, 10 days) using diquaternary ammonium as structuring agent. Compared to the conventional silicalite-1 material, the porous volume of the synthesized nanosheets determined from the N2 adsorption–desorption isotherms was found to be multiplied by 3.5 (0.62 cm3 g−1) without altering the microporous volume (0.18 cm3 g−1). This result was also confirmed by the increase of the n-hexane adsorption capacity and kinetics in the silicalite-1 nanosheets compared to the conventional silicalite-1. This approach indicates a new way for obtaining zeosil materials of controlled sizes and shapes for molecular decontamination.

Bridged polysilsesquioxane films via photoinduced sol–gel chemistry

The synthesis and characterization of bridged polysilsesquioxane films was performed via a photoacid-catalyzed sol–gel method using a series of three precursors with different organic moiety structures.

Self-Organized Poly(n-octadecylsilsesquioxane) Films via Sol–Gel Photopolymerization

We describe a novel solvent- and water-free sol-gel process for n-octadecyltriclorosilane (C(18)H(37)SiCl(3)) film catalyzed by photogenerated Brönsted acids. Driven by hydrophobic van der Waals interactions, a photoinduced self-assembly process occurs to afford a long-range ordered lamellar mesostructure, characterized by X-ray diffraction and transmission electron microscopy. Real-time Fourier transform IR spectroscopy was instrumental to probe the fast hydrolysis kinetics and assess the change of conformational behavior of the alkyl chains during UV irradiation. A unique combination of different solid-state NMR techniques ((29)Si, (13)C, (1)H) provided an insight into the supramolecular organization of this hybrid film.

Simultaneous sol–gel and anionic photopolymerization of 3-(glycidyloxypropyl)trimethoxysilanevia photobase catalysis

Type II polyether–silica hybrid films were successfully synthesized from 3-(glycidyloxypropyl)trimethoxysilane (GPTMS) through a novel photobase-catalyzed sol–gel and anionic polymerization using an α-amino acetophenone derivative as a tertiary amine photogenerator. We report here some characterization evidence establishing that the hybrid precursor undergoes two different polymerization reactions in a single step. FTIR analysis as well as solid-state NMR (13C, 29Si) shed light onto the tandem formation of the silica network and the polyether chains. The prominent role played by α-amino acetophenone in the dual catalysis was also highlighted by comparison with other O-acyloxime-based photobase generators.

Photoinduced synthesis and ordering of lamellar n-alkylsiloxane films†

Self-assembled organosilica films exhibiting various lamellar structures were prepared without solvent and watervia the fast photoacid-catalyzed sol–gel process of n-alkyltrimethoxysilanes (CnTMS, n = 8, 10, 12, 16 and 18). This facile photochemical route towards nanostructured hybrid films relies on superacid photocatalyst generated by the UV photolysis of a soluble lipophilic iodonium salt: (C12H25)2Φ2I+ SbF6−. A main emphasis has been on discussing the effect of the alkyl chain length on the level of ordering of the layered mesostructure (short- or long-range order), the alkyl chain packing arrangement (bilayered or interdigitated) and its conformational order (gauche and trans). X-Ray diffraction and electron microscopy (TEM and SEM) proved the high periodicity achieved with the long chain alkylsilanes (n = 16 and 18). Real-time Fourier transform infrared spectroscopy (RT-FTIR) was also instrumental in giving a unique insight into the sol–gel reaction kinetics and the progressive conformational ordering of the alkyl chains during the photoinduced self-assembly. Further, the combination of different solid-state NMR techniques (29Si and 13C) shed light on the siloxy layer microstructure and the conformational structure of the alkyl chain respectively.

Macroporous organosilica films via a template-free photoinduced sol–gel process

In the present work, we have designed a simple and original procedure for the spontaneous formation of macroporous organosilica films by photopolymerization-induced phase separation, avoiding the intervention of a template. The simple mixture of 3-(glycidyloxypropyl)trimethoxysilane (CH3O)3Si(CH2)3OCH2-CHCH2O (GPTMS), and poly(diethoxysiloxane) (C2H5O)2SiO)n (PDEOS, n ≈ 5), without solvent and water followed by UV illumination in the presence of a diaryl iodonium salt (photoacid generator) afforded macroporous hybrid films. This method relies on a single-step photoinduced sol–gel process with photogenerated Bronsted acids, resulting from the iodonium salt photolysis, which catalyse the hydrolysis–condensation reactions of both precursors. The formation of macropores was found to be strongly dependent on the concentration of PDEOS. It has been indeed proven that an increase in the fraction of PDEOS yielded macropores of increased diameters from 100 nm to 50 μm. In this study, our efforts have been focused on two essential aspects. On the one hand, the characterization of the macroporous films with regard to morphology, organic–inorganic microstructure and optical properties was commented upon thoroughly; on the other hand a general mechanism leading to the development of macropores was proposed and discussed.

Block Copolymer Self-Assembly in Mesostructured Silica Films Revealed by Real-Time FTIR and Solid-State NMR

Over the past ten years, understanding the self-assembly process within mesostructured silica films has been a major concern. Our characterization approach relies on two powerful and complementary techniques: in situ time-resolved FTIR spectroscopy and ex situ solid-state NMR. As model systems, three silica/surfactant films displaying various degrees of mesostructuration were synthesized using an amphiphilic block copolymer (PEO-b-PPO-b-PEO) via a UV light induced self-assembly process. The key idea is that the hydration state of the hydrophobic PPO chain is expected to be different depending upon whether the sample is amorphous (blend) or mesostructured (segregated). With real-time FTIR experiments, we show that the methyl deformation mode can act as a signature for the PPO microenvironment so as to trace the progressive copolymer self-association throughout the irradiation time. In (1)H solid-state NMR, the dependence of the (1)H chemical shift on the PPO hydration state has been exploited to evidence the extent of mesostructuration.

Thick mesostructured films via light induced self-assembly

As an alternative to solvent evaporation, we show that UV light can serve as a stimulus to promote self-assembly during the formation of surfactant-templated silica films. Despite practical and conceptual advantages, the Light Induced Self-Assembly (LISA) route has been poorly described in comparison with its evaporation induced analogue. In this article, we give an exhaustive overview of the potentiality of this photoinduced process using a range of PEO-b-PPO-b-PEO amphiphilic triblock copolymers, and investigating systematically the structural (29Si MAS NMR, XRD) and textural properties (TEM, N2 sorption) of the resultant worm-like mesostructured films. Practically, UV irradiation is applied directly to isotropic micrometric films consisting of a nonhydrolyzed alkoxide-amphiphilic copolymer-photoacid generator mixture, obviating the addition of solvent and water. Photoliberation of Bronsted photoacid generates on demand hydrophilic silica species, driving the micellization of the copolymer. The process is single-step and fast, yielding transparent mesostructured films within a few seconds. A target addressed in this feature is to investigate the film structural evolution resulting from the UV irradiation by in situ Fourier transformed infrared analysis (FTIR). Without the interference of solvent, this powerful technique provides a new perspective on the course of the sol–gel process in mesostructured films. For the first time, hydrolysis is assessed kinetically as well as the silica network condensation and the water content of the film.