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International audience; This study proposes a novel sepiolite-based Aquivion electrolyte membrane which could be operated at low relative humidity. In the study, it was discovered that the functionalization of sepiolite with fluorinated groups (i.e., -C7F15), named SEP-F, helps its dispersion in the composite membrane, compared with the use of natural sepiolite. The Aquivion/SEP-F composite membrane showed increased water uptake, thermo-mechanical and chemical stability as well as proton conductivity and decreased swelling compared with commercially available Nafion HP and pristine Aquivion. Their behavior in single cell MEA testing conditions was also assessed. Aquivion/SEP-F composite membrane can be an interesting alternative for low relative humidity operation of PEMFC (proton exchange membrane fuel cell).

This study introduces the relationship between physicochemical properties and blending time for two different clays, sepiolite nanofibers (SEP) and halloysite nanotubes (HNT) inside a Nafion matrix...

International audience; A facile method to synthesize light weight thermally superinsulating composite aerogel is being presented here. A polymethylsilsesquioxane (PMSQ) – cellulose composite aerogel starting from a trifunctional precursor viz. methyltrimethoxysilane (MTMS) and kapok fibers have been synthesized. Kapok fibers have been employed as they have a homogeneous hollow structure and also possess intrinsic low density. A PMSQ-Kapok composite aerogel with a density as low as 0.053 gcm−3 with a thermal conductivity of 0.018 W m−1 K−1 in room conditions has been synthesized. Besides, a flexural strength (at maximum stress) of 108 kPa ± 21 has been obtained through three points bending test. All the composite aerogels are mesoporous as characterized by N2 sorption isotherms and hydrophobic as shown by sessile drop experiments. On comparison with the earlier reported works and with some of the commercially available aerogel composites, the current results seem promising. For demonstrating the real application purpose, thin composite aerogel sheets have also been synthesized which could be easily rolled/bended.

Aerogels are highly porous, ultra-light (density around 0.1 g/cm3) nanostructured materials. One of their most extraordinary properties is thermal super-insulation, i.e. thermal conductivity below that of the air: 0.015 vs 0.025 W/(m.K) in room conditions. However, classical silica aerogels are extremely fragile and organic/synthetic (resorcinol-formaldehyde) aerogels may include toxic components, which hinders their wide application. Bio-aerogels are a new generation of aerogels made from biomass-based polymers, mainly polysaccharides. We prepared aerogels from cellulose (“aerocellulose” /1, 2/) and pectin (“aeropectin” /3/) via polymer dissolution, coagulation and drying with super-critical CO2. Their density varies from 0.05 to 0.2 g/cm3 and specific surface area is around 200-300 m2/g. Bio-aerogels are mechanically strong, with Young’s moduli from 1-2 to 20-30 MPa and plastic deformation up to 60-70% strain before the pore walls collapse. Aeropectin thermal conductivity turned to be around 0.015 – 0.020 W/(m.K) making it the first reported thermal super-insulating fully biomass-based aerogel. The thermal conductivity of aerocellulose is rather “high”, around 0.030-0.035 W/(m.K), due to the presence of large macropores. We demonstrate that by using polysaccharide functionalization and making polymer-silica aerogel hybrids it is possible to vary specific surface area (increase to 800-900 m2/g) and decrease aerogel thermal conductivity below that of the air.

International audience; Silica aerogels are excellent thermal insulators, but their brittle nature has prevented widespread application. To overcome these mechanical limitations, silica–biopolymer hybrids are a promising alternative. A one-pot process to monolithic, superinsulating pectin–silica hybrid aerogels is presented. Their structural and physical properties can be tuned by adjusting the gelation pH and pectin concentration. Hybrid aerogels made at pH 1.5 exhibit minimal dust release and vastly improved mechanical properties while remaining excellent thermal insulators. The change in the mechanical properties is directly linked to the observed “neck-free” nanoscale network structure with thicker struts. Such a design is superior to “neck-limited”, classical inorganic aerogels. This new class of materials opens up new perspectives for novel silica–biopolymer nanocomposite aerogels.

International audience; Preface : In September 2016, the “Third International Seminar on Aerogels”, co-organized with the International Society for the Advancement of Supercritical Fluids (ISASF) and Technical University of Hamburg-Harburg (TUHH) was hosted by MINES ParisTech in Sophia Antipolis (Alpes-Maritimes, France). This Special Issue gathers 17 full original articles related to topics and presentations of this event.

International audience; Increasing the activity of a photocatalyst goes through the improvement of both its absorption (light) and adsorption (reactant) properties. For a given semiconducting material, the charge carrier separation is also a very important step. Properly combining chosen phases is one option to improve this separation (example of the commercial P25) and depositing platinum on the surface of the catalyst, another one. In some cases, coupling both may nevertheless lead to a decrease of photoactivity or at least limit the potentiality of the catalyst. A third option, consisting in modifying the morphology of the photoactive phase, has shown very promising results. In this study, we have elaborated, characterized and evaluated the hydrogen evolution potentiality (through methanol assisted water splitting) of different TiO2 morphologies: nanoparticles, nanotubes and aerogels. These materials have shown different behaviours depending on both their composition and morphology. Different types of separation processes have been claimed to account for the observed different photoactivities, with more or less pronounced synergetic effects, due to: the use of Pt as a co-catalyst, the mixture of different TiO2 phases (anatase and TiO2(B) or rutile) and the specific morphology of the samples (nanotubes or aerogels). Among all the tested samples, the TiO2 aerogel supported Pt one exhibited very promising performances, three times as active as P25 supported Pt, which is already much more active than pure P25 in our testing conditions.

A series of hybrid supported catalysts was prepared by sequentially grafting Cp 2 ZrCl 2 and ( n BuCp) 2 ZrCl 2 (1:3 ratio) onto synthesized xerogel, aerogel and commercial silicas. Supports and catalysts were characterized by Rutherford backscattering spectrometry, energy-dispersive X-ray scanning electron microscopy, atomic force microscopy and nitrogen adsorption. Grafted metal content laid between 0.15 and 0.5 wt.% Zr/SiO 2 . All the systems were shown to be active in ethylene polymerization with methylaluminoxane as the co-catalyst. Catalyst activity and molecular weight were shown to depend on the textural characteristic of the silicas, namely grain size and pore diameter. The highest activity in ethylene polymerization (ca. 5310 kg PE mol Zr −1 h −1 ) was obtained with the supported catalyst using commercial silicas with average particle size around 50 μm. Particles with sizes of 80–90 μm obtained less activity. Resulting polymers were characterized by gel permeation chromatography and differential scanning calorimetry.

A silyl-functionalized benzazole dye, fluorescent by excited state intramolecular proton transfer (ESIPT) mechanism, was synthesized by reacting 2-(2'-hydroxyphenyl)benzoxazole with 3-(triethoxysilyl)propyl isocyanate. The fluorescent silica gel was prepared by the addition of a solution of 2-propanol and the fluorescent dye after the gelation time. The monolithic aerogel was obtained via supercritical CO 2 drying of the fluorescent gel. The resulting aerogel is transparent in the visible light and fluorescent in the blue-green region under UV radiation.

Previously published results have shown that washing and aging treatments (respectively in water/ethanol and water/polyethoxydisiloxane solutions) of silica gels (synthesized from polyethoxydisiloxane precursors through HF catalysis) significantly enhance both the permeability and mechanical properties of the wet gels. Unfortunately, scaling-up the process induces severe cracks during supercritical drying. This phenomenon has been related to a pore-size distribution gradient between the surface and the bulk of the gel that appears after aging of thick gels. We report efforts to optimize the aging step. Aging in less-concentrated polyethoxydisiloxane solutions yields gels with a more homogeneous pore-size distribution and has enabled us to obtain large monolithic and crack-free aerogels that remain light and transparent.

International audience; Evaporative drying of polyurethane-based gels produces xerogels. Supercritical drying after replacement of interstitial liquid by supercritical CO2 produces aerogels. SEM micrographs show that both materials are made up of small size particles gathered up in filament-shaped, strongly cross-linked aggregates. Density measurements show that they both have a large pore volume. When submitted to mercury porosimetry, the behavior of these materials is similar to that of inorganic aerogels, as previously observed. Mercury does not penetrate the pore network, but the whole material is densified. The usual Washburn equation cannot be used to analyze the mercury porosimetry. A well-suited equation based on a buckling model of filament-shaped aggregates has been developed in order to determine the pore volume distribution of mineral dried gels. This equation is also valid for analyzing the texture of organic hyperporous materials like polyurethane dried nanoporous gel. © 2003 Elsevier Science Ltd. All rights reserved.

Silica gels form a large family of materials, obtained from more or less complex processes; their elaboration involves several steps that basically include a sol gel transition or a precipitation, ...

International audience; Large monolithic crack-free transparent silica aerogels were prepared by a patented sol-gel route, and then directly washed and dried with supercritical CO2. In order to characterise as precisely as possible the apparent thermal conductivity of such superinsulating materials, two methods were developed (so-called hot-band and micro-fluxmeter techniques) and the results obtained at room temperature and atmospheric pressure were compared with the standard hot-wire measurements under the same conditions. A reproducibility study showed no large deviations between the thermal conductivities obtained by these different techniques. This leads to the conclusion that aerogels prepared in this way present a good thermal and optical compromise (low thermal conductivity, high light transmission, and no significant radiative heat transport component at room temperature) and can be considered as transparent superinsulating materials.

6th International Symposium on Aerogels (ISA-6) Albuquerque, New Mexico, October 08-11, 2000; International audience; Recent investigations have shown that the structure of organic aerogels can be significantly modified by changing the precursors, the solvent and the nature of the catalyst involved in the sol-gel reaction. It is therefore highly desirable to investigate the sol-gel mechanism. For this purpose, dynamic light scattering (DLS) measurements have been performed at different stages of the reaction for base- or acid-catalyzed gelation of resorcinol-formaldehyde (RF) using water or acetone as solvents. The structure of aged gels was investigated by small-angle X-ray scattering (SAXS) and compared to that of the aerogels obtained after exchange of solvent by supercritical CO2 and drying of the aged gels. It is shown that acid-catalyzed gelation of RF in acetone can be described by percolation, which explains that this series of aerogels consists of mass fractal aggregates (Dm = 2.5). The partial collapse of this polymeric gel yielding colloidal particles in the aerogel can be attributed to deswelling in supercritical CO2. DLS indicates that gelation of RF with a base catalyst yields a colloidal gel whose structure remains practically unchanged in the aerogel, as shown by SAXS.

International audience; This chapter focuses on isocyanurate and cellulose-based aerogels. First, it presents the global sol-gel synthetic path by polycondensation. Then, it summarizes all the main results on these two families of organic aerogels. Finally, some of the recent advancements concerning their use for hybridization of silica aerogels are shortly presented. Through a brief description of the basics, together with a short overview of the main properties, this article highlights the huge potential of those two classes of urethane-based aerogels.

International audience; The present chapter is focused on describing the intimate link which exists between aerogels and thermal superinsulation. For long, this applied field has been considered as the most promising potential market for these nanostructured materials. Most likely this old vision will become reality in the near future.Following a short presentation of the global need for superinsulation together with a closer look at the specific situation in the building sector, we propose within this synopsis a brief analysis of (1) the world's insulation markets, (2) superinsulating aerogel materials and their alternatives, (3) commercial aerogel insulation products available today, and (4) our estimation of their most likely applications worldwide in the future. We conclude this chapter with some first considerations on health, toxicity, and environmental aspects.Based on recent developments in the field, it can be stated that aerogels still offer the greatest potential for nonevacuated superinsulation systems and consequently must be considered as an amazing opportunity for sustainable development. This chapter of the handbook bridges the gap between those dealing with thermal insulation properties of aerogel materials in general (Chap. 21) and the various commercial products described in Part XV.

International audience; A series of silica-based materials were employed as sorbents within solid-phase microextraction vials. The aim of the study was to evaluate the effect of an additional phase on the distribution of the volatile and less volatile analytes. The adsorption of six probe molecules, namely isoamyl acetate, ethyl hexanoate (ethyl caproate), phenylethyl alcohol, ethyl octanoate (ethyl caprilate), 2-phenylethyl acetate, and ethyl decanoate, was monitored by detecting the desorbed amount on a DVD-CAR-PDMS fiber from Pilsen beer. The microextraction process involved the presence of different silica-based phases produced via different methods: xerogel produced by hydrolytic and non-hydrolytic routes, aerogel, pyrogenic, and precipitated silica. The resulting data are discussed in correlation with sorbent texture properties (specific area and pore diameter). The modification of silica with alkyl groups also affects the preconcentrated amount of the target molecules in the headspace. The presence of sorbents was shown to affect the analyte signal more than the addition of NaCl or the use of ultrasound.

Five silyl-functionalized benzazole dyes, fluorescent by excited state intramolecular proton transfer (ESIPT) mechanism, were synthesized by reaction of amino benzazole derivatives with 3-(triethoxysilyl)propyl isocyanate. Fluorescent silica gels were prepared and monolithic aerogels (d ≈ 0.18 g cm−3) were obtained via supercritical CO2 drying of the fluorescent gel. The photophysical behaviour of the dyes and fluorescent silica aerogels was investigated by UV–vis and steady-state fluorescence spectroscopy.

International audience; Novel various aerogel-like materials were prepared from the biomass, cellulose and cellulose derivatives, either from their solutions or via physical or chemical gelation and drying in CO2 under supercritical conditions. Two classes of materials will be discussed: based on pure cellulose and on cellulose acetate. Pure cellulose highly porous material, Aerocellulose, was made from cellulose dissolved in green solvents, aqueous NaOH or ionic liquids. An overview of the main preparation steps is given, from cellulose dissolution and solution-state properties, to regeneration kinetics, solvent exchange and drying. The porosity of Aerocellulose is higher than 90% with pore sizes from a few tens of nanometers to a few tens of micrometers. The density ranges from 0.06 to 0.3 g/cm3. Aerogels based on cellulose acetate were synthesised by crosslinking cellulose acetate dissolved in acetone with a non-toxic isocyanate as a cross-linker, using different catalysts (dibutyltin dilaurate, a triethylamine and pyridine). Mesoporous nanostructured network was obtained after drying; pore sizes vary from 10 to 30 nm and density from 0.25 to 0.85 cm3/g. Two applications of these new materials are discussed: as thermal insulators and carbons in proton exchange membrane fuel cell.