Pectin aerogels, with very low density (around 0.1 g cm−3) and high specific surface area (up to 600 m2 g−1), are excellent thermal insulation materials since their thermal conductivity is below that of air at ambient conditions (0.025 W m−1 K−1). However, due to their intrinsic hydrophilicity, pectin aerogels collapse when in contact with water vapor, losing superinsulating properties. In this work, first, pectin aerogels were made, and the influence of the different process parameters on the materials’ structure and properties were studied. All neat pectin aerogels had a low density (0.04–0.11 g cm−1), high specific surface area (308–567 m2 g−1), and very low thermal conductivity (0.015–0.023 W m−1 K−1). Then, pectin aerogels were hydrophobized via the chemical vapor deposition of methyltrimethoxysilane using different reaction durations (2 to 24 h). The influence of hydrophobization on material properties, especially on thermal conductivity, was recorded by conditioning in a climate chamber (25 °C, 80% relative humidity). Hydrophobization resulted in the increase in thermal conductivity compared to that of neat pectin aerogels. MTMS deposition for 16 h was efficient for hydrophobizing pectin aerogels in moist environment (contact angle 115°) and stabilizing material properties with no fluctuation in thermal conductivity (0.030 W m−1 K−1) and density for the testing period of 8 months.

In this work, we focus on a novel sepiolite-incorporated Aquivion composite membrane that can be operated in a proton-exchange membrane fuel cell (PEMFC) at a relative humidity (RH) below 30%. The maximum power density reduction of the developed membrane is only 0.77% at 30% RH. In the study, we demonstrated adding sepiolite grafted with fluorination groups enhanced the homogeneity of the composite membrane prepared with Aquivion compared to composite membranes prepared with natural sepiolite. In addition to functionalization, a specific acidic post-treatment enhanced fuel cell performance. The acidic treatment was intended to remove some of the Fe cations in the sepiolite to prevent Aquivion degradation. Although this effect was not evident, this treatment removed some of the Al and Mg cations, resulting in a more amorphous structure of fluorinated sepiolite with increased porosity, roughness, and lumen. This significantly enhanced the proton diffusion in the composite membranes. Compared to commercially available membranes and membranes developed by other research groups, the Aquivion/fluorinated and post-treated sepiolite composite membranes (Aq/pSEP-F5) exhibited increased swelling behavior, water uptake, mechanical property, chemical stability, proton conductivity, cell voltage, and maximum power density in the Membrane Electrode Assembly (MEA). Thus, they are highly advantageous and a promising alternative for the functioning of PEMFC at low relative humidity.

This chapter focuses on the use of aerogel materials as superinsulation. For long, this applied field has been considered as the most promising potential market for these nanostructured materials. The exciting developments of the last 20 years strongly support this old vision. Following a short presentation of the global need for superinsulation, we give an overview on the relevant physical principles and classify the existing superinsulating materials besides aerogels. We then take a look at the chemistry and the characteristics of aerogel materials and describe the currently available commercial aerogel products. We quantify the global insulation and superinsulation markets followed by a presentation of the most relevant application areas of aerogel as superinsulation: the built environment, offshore oil and gas, industrial insulation, apparel, and aerospace. Based on recent developments in the field, aerogels still offer the greatest potential for non-evacuated superinsulation systems and consequently are 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. 9 by Hans-Peter Ebert) and the various commercial products described in Part X.

The present review is focused on one of the most studied aerogel materials, silica aerogels. It aims at presenting a brief overview of the elaboration steps (sol–gel synthesis, ageing, and drying), the textural and chemical characteristics (aggregation features, porosity and surface chemistry), the main physical properties (from thermal, mechanical, acoustical, and optical to biological, medical, etc.) and a rather broad panel of related potential applications of these fascinating nanostructured materials. It cannot be considered as an exhaustive synopsis but must be used as a simple tool to initiate further bibliographic studies on silica aerogels, which are amazing very light solid materials, as shown in Fig. 13.1.

The proton exchange membrane (PEM) is pivotal among the various components of proton exchange membrane fuel cells (PEMFCs). From the many PEMs, perfluorosulfonic acid and non-fluorinated hydrocarbon electrolyte membranes are used in PEMFC operation, but they have a limited performance above 90 degrees C and at a relative humidity (RH) below 50%. Hence, the incorporation of nanoclay, an inorganic filler, into polymer matrixes has been attempted to improve the performance of PEMs. Nanoclays, such as montmorillonite and laponite in a layered silicate morphology, sepiolite nanofibers and halloysite nanotubes, with their fiber morphologies, and layered double hydroxide are attractive for composite membranes because they improve the hydrophilicity, hygroscopicity, and thermal stability of composite membranes at intermediate temperatures and low RH. The introduction of nanoclays also improves the mechanical properties. Furthermore, nanoclays are cost-competitive among the nanomaterials, thereby offering the potential to reduce composite membranes costs. This review highlights the preparation of composite membranes containing sulfonic, perfluorosulfonic, and amine groups, and other types of functionalized nanoclays, as well as the characterization of the composite membranes and cell performances operating at low RH.

Executive Summary: In the context of global climate control policies, improving the energy efficiency of existing buildings represents a great challenge, worldwide as well as at the European level. Reducing the energy consumption of buildings is nowadays preferably achieved by increasing the thermal resistance of the insulation layer in the building envelope. The AEROCOINs project, in order to contribute to the future reduction of energy consumption by decreasing heating and cooling demands of existing-buildings, has been working on the clever combination of sol-gel science and nanotechnology aiming to advance on the design and development of

Aquivion membrane displays improved properties as compared to Nafion membrane, partly due to shorter side chains. However, some improvements are still necessary for proton exchange membrane fuel cell to operate at low relative humidity. To overcome this drawback, the addition of clay nanoparticle into the Aquivion matrix can be considered. In this study, different composite membranes have been prepared mixing short-side-chain PFSA (perfluorosulfonic acid) Aquivion and selectively modified halloysite nanotubes for PEMFC low relative humidity operation. Halloysites were grafted with fluorinated groups, sulfonated groups, or perfluoro-sulfonated groups on inner or outer surface of the tubes. The obtained composite membranes showed improved properties, especially higher water uptake associated with reduced swelling and better mechanical strength compared to pristine Aquivion membrane and commercially available Nafion HP used as reference. The best performance in this study was obtained with Aquivion loaded with 5 wt% of pretreated perfluoro-sulfonated halloysite. The composite membrane, referred to as Aq/pHNT-SF5, displayed the largest water uptake and proton conductivity among the panel of membranes tested. The chemical stability was not affected by the presence of halloysite in the Aquivion matrix.

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 aemgel 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 N-2 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.

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...

Short (<2.5 mm) cellulose fiber–silica composite aerogels were synthesized by dispersing cellulose fibers in polyethoxydisiloxane-based sol. After in situ gelation, silica phase was hydrophobized with hexamethyldisilazane, and the composites were dried either at ambient pressure or with supercritical (sc) CO 2 . Fiber concentration was varied from 0 to 25 wt% (corresponding to 0–2.1 vol%) of the final dried composite. Preformed cellulosic fiber network preserved the monolithic shape of the silica-based composites during ambient drying. At room conditions, thermal conductivities were 0.015 ± 0.001 W/(m K) for sc-dried aerogels and 0.017 ± 0.001 W/(m K) for their ambient-dried counterparts. Materials dried with either method exhibited large specific surface areas, from 570 to 730 m 2 /g, and SEM analysis did not show significant differences in the global structure of the silica network. Composite aerogels were hydrophobic with water contact angles around 138°. Based on this proof of concept, the same approach was used with a variety of natural and recycled cellulosic fibers also resulting in silica-based monoliths with low thermal conductivities in the 0.016–0.023 W/(m K) range, all produced via ambient drying.

Short man-made cellulose fibers (TENCEL® fibers) were used to mechanically reinforce thermal superinsulating silica aerogels. The aerogels were prepared via two drying techniques: ambient pressure drying and with supercritical CO2, in both cases resulting in monolithic non-brittle materials. The influence of fiber length and concentration on the thermal conductivity and flexural properties of both types of composite aerogels was evaluated. Thermal conductivity in room conditions varied from 0.015 to 0.018W/mK; it slightly increased with fiber concentration but remained in superinsulation domain. The importance of fiber percolation concentration for synthesizing monolithic ambient pressure dried composite aerogels was demonstrated. Contrary to neat silica aerogels, non-brittle behavior was observed for composite aerogels regardless of the drying method when reinforced with cellulose fibers. Macroscopic short cellulose based fibers are efficient and easy to use for preparing robust, monolithic, thermal superinsulating aerogel materials.

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.

This chapter focuses on one of the most studied aerogel materials, silica aerogels. It aims at presenting a brief overview of the elaboration steps (sol–gel synthesis, aging, and drying), the textural and chemical characteristics (aggregation features, porosity, and surface chemistry), the main physical properties (from thermal, mechanical, acoustical, and optical, to biological, medical, etc.), and a rather broad panel of related potential applications of these fascinating nanostructured materials. It cannot be considered as an exhaustive synopsis but must be used as a simple tool to initiate further bibliographic studies on silica aerogels.

Silica-based aerogels have been studied for many decades for thermal superinsulation applications. Commercial products exhibiting excellent thermal insulation properties are already available on the market but ambient-drying routes are still intensively studied in order to compete with supercritical drying and further reduce associated costs of production. One of the main issues concerns preservation of monolithicity of the wet gels via ambient-drying. Most known works were related to use of non-woven fibrous mats to produce so-called blankets. Additionally, recent studies have demonstrated that it is possible to obtain superinsulating silica-based monoliths by using Ormosils precursors at lab-scale [1]. Within the present study, we have demonstrated that it is also possible to maintain macroscopic cohesion of the silica phase by using short cellulosic fibers and still working with TEOS. These ambient-dried monolithic organic-inorganic composites present morphological, structural and thermal properties similar to those of their supercritical CO2 counterparts. The presence of fibers lead to a significant improvement of mechanical properties as shown by 3-points bending characterization. Compared to pure silica samples, brittle behavior disappears but more interesting, ambient-dried composites appear more ductile than the supercritically dried ones. Proof of concept was first demonstrated with reference cellulosic fibers (Tencel® product coming from Lyocel process). Then this lab-scale method was extended successfully to other cellulose based fibers such as wood and flax. Using different fiber geometries and concentrations as well as alternative fibers allowed us to achieve levels of thermal conductivity lower than 0.015 W/m.K in room conditions. We will present global processing route, materials properties, comparison with supercritical drying and effect of fiber concentration and length on the properties of the composites. [1] Hayase G, Kanamori K, Maeno A, Kaji H, Nakanishi K (2016) Dynamic spring-back behavior in evaporative drying of polymethylsilsesquioxane monolithic gels for low-density transparent thermal superinsulators, J Non-Cryst Solids 434:115-119

Organic-inorganic composite aerogels were synthesized via a facile one-step impregnation of a wet hydrophobic cellulose II matrix with polyethoxydisiloxane solution followed by in situ NH4OH-catalysed formation of a nanostructured mesoporous silica network. The silica phase was subsequently hydrophobised with hexamethyldisilazane. By tuning synthesis conditions, organic-inorganic composite aerogels with various morphology (from meso- to macroporous), specific surface area (from 200 to 850m2/g) and hydrophilic-hydrophobic balance (from fully hydrophilic to highly hydrophobic) were prepared after supercritical CO2 drying. The obtained organic-inorganic aerogels are monolithic, resistant to humidity and thermally superinsulating with the thermal conductivity 0.021–0.022W/(m·K) in room conditions.

The Third International Seminar on Aerogels took place on 22 – 23 September 2016 in Sophia Antipolis (France) at MINES ParisTech. Researchers from more than 25 countries and representatives of industry used two days to exchange views and ideas on the production, processing, and applications of aerogels from inorganic and organic materials. Aerogels from different precursors like silica, metal oxides, polyurethanes, urea, proteins, polysaccharides and their composites were presented to the auditorium. Structure and properties of new aerogels produced with common and new gelation and drying processes were shown. Aerogels were functionalized regarding their hydrophilicity, mechanical stability, and drug release properties via embedding of elements or fibres or coating. Modelling of gelation and drying of aerogels for scale up and transfer of processes to new products were presented. Scale-up strategies for existing processes were discussed to enable the next step to industrial production of aerogels. Besides improved aerogels for insulation applications and encapsulation of drugs or bioactive components for foods, new possible inorganic and organic aerogel applications, like electrical applications (capacitors, batteries), aerogels for catalysis, foods and packaging, as well as membranes for pumps were pointed out. 150 oral and poster research communications were accomplished with the presentations of the latest industrial achievements allowing learning from the “first hand” about the new aerogel materials and prospects in their applications. The conference ended with an aerogel art show. The seminar was possible thanks to the sponsoring of several European, American and Japanese industrial companies (Aerogel technologies, ASPEN, BASF, ENERSENS, NATEX, PAREX Group, TIEM Factory) and the local community (CASA), and to the strong support of MINES-ParisTech.