Aerogels 2018

A special issue of Gels (ISSN 2310-2861).

Deadline for manuscript submissions: closed (27 May 2018) | Viewed by 72901

Special Issue Editors


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Guest Editor
Institut Charles Gerhardt-Montpellier, Matériaux Avancés pour la Catalyse et la Santé, UMR5253 CNRS-ENSCM-UM2-UM1, 8 rue de l'Ecole Normale, 34296 Montpellier, France
Interests: polysaccharides; aerogel; textural properties; self-assembly; chemical modification; catalysis; medical devices
Special Issues, Collections and Topics in MDPI journals

E-Mail Website
Guest Editor
Institut Charles Gerhardt-Montpellier, Matériaux Avancés pour la Catalyse et la Santé, UMR5253 CNRS-ENSCM-UM2-UM1, 8 rue de l'Ecole Normale, 34296 Montpellier, France
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

As you know well, “aerogel” is a broad term used for a special class of ultra-light porous materials. An aerogel is formed when a gel retains the structure of the parent gel upon drying, thus resulting in a highly porous material. These amazing materials provide advantages in terms of surface area, diffusion properties, thermal conductivity, refractive index, and dielectric constant. Thus, aerogels of inorganic or organic/bio-organic gels can find applications in a variety of domains, from super insulation and supercapacitors to trapping of molecules and biological entities, adsorbent, catalysts, sensors, and biomedical devices.

This Special Issue will provide an international forum for researchers to discuss the most recent studies concerning the preparation, characterization and applications of such aerogels. Through this Special Issue, the present state and future will be discussed by a wide range of authors.

Dr. Francoise Quignard
Dr. Nathalie Tanchoux
Guest Editors

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Keywords

  • aerogels
  • textural properties
  • thermal conductivity
  • biomedical scaffold
  • drug release

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Published Papers (11 papers)

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Editorial

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3 pages, 192 KiB  
Editorial
Editorial on Special Issues “Aerogels” and “Aerogels 2018”
by Françoise Quignard and Nathalie Tanchoux
Gels 2020, 6(3), 19; https://doi.org/10.3390/gels6030019 - 29 Jun 2020
Viewed by 2154
Abstract
Aerogels can be defined as ultralight materials with a 3D porous structure, similar to their parent wet gels, where the solvent has been replaced by a gas without a collapse of the gel structure, thanks to the drying process used (supercritical CO2 [...] Read more.
Aerogels can be defined as ultralight materials with a 3D porous structure, similar to their parent wet gels, where the solvent has been replaced by a gas without a collapse of the gel structure, thanks to the drying process used (supercritical CO2 drying, freeze drying, etc [...] Full article
(This article belongs to the Special Issue Aerogels 2018)

Research

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16 pages, 4240 KiB  
Article
Influence of Structure-Directing Additives on the Properties of Poly(methylsilsesquioxane) Aerogel-Like Materials
by Marta Ochoa, Alyne Lamy-Mendes, Ana Maia, António Portugal and Luísa Durães
Gels 2019, 5(1), 6; https://doi.org/10.3390/gels5010006 - 28 Jan 2019
Cited by 9 | Viewed by 3580
Abstract
The effect of glycerol (GLY) and poly(ethylene glycol) (PEG) additives on the properties of silica aerogel-like monoliths obtained from methyltrimethoxysilane (MTMS) precursor was assessed. The tested molar ratios of additive/precursor were from 0 to 0.1 and the lowest bulk densities were obtained with [...] Read more.
The effect of glycerol (GLY) and poly(ethylene glycol) (PEG) additives on the properties of silica aerogel-like monoliths obtained from methyltrimethoxysilane (MTMS) precursor was assessed. The tested molar ratios of additive/precursor were from 0 to 0.1 and the lowest bulk densities were obtained with a ratio of 0.025. When a washing step was performed in the sample containing the optimum PEG ratio, the bulk density could be reduced even further. The analysis of the material’s microstructure allowed us to conclude that GLY, if added in an optimum amount, originates a narrower pore size distribution with a higher volume of mesopores and specific surface area. The PEG additive played a binder effect, leading to the filling of micropores and the appearance of large pores (macropores), which caused a reduction in the specific surface area. The reduction of the bulk density and the microstructural changes in the aerogels induced by adding a small amount of these additives confirm the possibility of fine control of properties of these lightweight materials. The achieved high porosity (97%) and low thermal conductivity (~35 mW·m−1·K−1) makes them suitable to be used as thermal insulators. Full article
(This article belongs to the Special Issue Aerogels 2018)
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11 pages, 3630 KiB  
Article
Millimeter-Size Spherical Polyurea Aerogel Beads with Narrow Size Distribution
by Despoina Chriti, Grigorios Raptopoulos, Maria Papastergiou and Patrina Paraskevopoulou
Gels 2018, 4(3), 66; https://doi.org/10.3390/gels4030066 - 6 Aug 2018
Cited by 21 | Viewed by 5606
Abstract
We report the room temperature synthesis of spherical millimeter-size polyurea (PUA) aerogel beads. Wet-gels of said beads were obtained by dripping a propylene carbonate solution of an aliphatic triisocyanate based on isocyanurate nodes into a mixture of ethylenediamine and heavy mineral oil. Drying [...] Read more.
We report the room temperature synthesis of spherical millimeter-size polyurea (PUA) aerogel beads. Wet-gels of said beads were obtained by dripping a propylene carbonate solution of an aliphatic triisocyanate based on isocyanurate nodes into a mixture of ethylenediamine and heavy mineral oil. Drying the resulting wet spherical gels with supercritical fluid (SCF) CO2 afforded spherical aerogel beads with a mean diameter of 2.7 mm, and a narrow size distribution (full width at half maximum: 0.4 mm). Spherical PUA aerogel beads had low density (0.166 ± 0.001 g cm–3), high porosity (87% v/v) and high surface area (197 m2 g–1). IR, 1H magic angle spinning (MAS) and 13C cross-polarization magic angle spinning (CPMAS) NMR showed the characteristic peaks of urea and the isocyanurate ring. Scanning electron microscopy (SEM) showed the presence of a thin, yet porous skin on the surface of the beads with a different (denser) morphology than their interior. The synthetic method shown here is simple, cost-efficient and suitable for large-scale production of PUA aerogel beads. Full article
(This article belongs to the Special Issue Aerogels 2018)
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9 pages, 1569 KiB  
Article
Prevention of the Aggregation of Nanoparticles during the Synthesis of Nanogold-Containing Silica Aerogels
by István Lázár and Hanna Judit Szabó
Gels 2018, 4(2), 55; https://doi.org/10.3390/gels4020055 - 19 Jun 2018
Cited by 16 | Viewed by 5150
Abstract
Nanogold is widely used in many areas of physics and chemistry due to its environment-sensitive plasmon resonance absorption. The immobilization of gold nanoparticles in highly porous silica aerogel offers an attractive alternative to liquid gold solutions as they show a mechanically stable structure, [...] Read more.
Nanogold is widely used in many areas of physics and chemistry due to its environment-sensitive plasmon resonance absorption. The immobilization of gold nanoparticles in highly porous silica aerogel offers an attractive alternative to liquid gold solutions as they show a mechanically stable structure, are permeable to gases, and can even be used at elevated temperatures. We have found that the commercially available citrate-stabilized 10 nm gold nanoparticles may suffer from aggregation prior to or under the base-catalyzed gelation process of tetramethoxy silane. In the wet gels, Au particles increased in size, changed shape, and demonstrated the loss of plasmon resonance absorption, due to the formation of larger aggregates. We have studied a range of water-miscible organic solvents, stabilizing agents, and the gelation conditions to minimize changes from occurring in the aerogel setting and the supercritical drying process. It has been found that atmospheric carbon dioxide has a significant effect on aggregation, and it cannot be entirely excluded under normal synthetic conditions. Methanol resulted in an increase in the particle size only, while dimethyl sulfoxide, dimethylformamide, and urea changed the shape of nanoparticles to rod-like shapes, and diols led to an increase in both size and shape. However, using the polymeric stabilizer poly(vinyl pyrrolidone) efficiently prevented the aggregation of the particles, even in the presence of high concentrations of carbon dioxide, and allowed the production of nanoAu containing silica aerogels in a single step, without the modification of technology. Full article
(This article belongs to the Special Issue Aerogels 2018)
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13 pages, 3422 KiB  
Article
Advanced Recycled Polyethylene Terephthalate Aerogels from Plastic Waste for Acoustic and Thermal Insulation Applications
by Hong Wei Koh, Duyen K. Le, Gek Nian Ng, Xiwen Zhang, Nhan Phan-Thien, Umeyr Kureemun and Hai M. Duong
Gels 2018, 4(2), 43; https://doi.org/10.3390/gels4020043 - 17 May 2018
Cited by 71 | Viewed by 9970
Abstract
This work presents for the first time, a simple, practical and scalable approach to fabricating recycled polyethylene terephthalate (rPET) aerogels for thermal and acoustic insulation applications. The rPET aerogels were successfully developed from recycled PET fibers and polyvinyl alcohol (PVA) and glutaraldehyde (GA) [...] Read more.
This work presents for the first time, a simple, practical and scalable approach to fabricating recycled polyethylene terephthalate (rPET) aerogels for thermal and acoustic insulation applications. The rPET aerogels were successfully developed from recycled PET fibers and polyvinyl alcohol (PVA) and glutaraldehyde (GA) cross-linkers using a freeze-drying process. The effects of various PET fiber concentrations (0.5, 1.0 and 2.0 by wt.%), fiber deniers (3D, 7D and 15D) and fiber lengths (32 mm and 64 mm) on the rPET aerogel structures and multi-properties were comprehensively investigated. The developed rPET aerogels showed a highly porous network structure (98.3–99.5%), ultra-low densities (0.007–0.026 g/cm3), hydrophobicity with water contact angles of 120.7–149.8°, and high elasticity with low compressive Young’s modulus (1.16–2.87 kPa). They exhibited superior thermal insulation capability with low thermal conductivities of 0.035–0.038 W/m.K, which are highly competitive with recycled cellulose and silica-cellulose aerogels and better than mineral wool and polystyrene. The acoustic absorption results were also found to outperform a commercial acoustic foam absorber across a range of frequencies. Full article
(This article belongs to the Special Issue Aerogels 2018)
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10 pages, 42133 KiB  
Article
The Relation between the Rheological Properties of Gels and the Mechanical Properties of Their Corresponding Aerogels
by Mingze Sun, Hua Sun, Yutao Wang, Miguel Sánchez-Soto and David A. Schiraldi
Gels 2018, 4(2), 33; https://doi.org/10.3390/gels4020033 - 9 Apr 2018
Cited by 33 | Viewed by 6306
Abstract
A series of low density, highly porous clay/poly(vinyl alcohol) composite aerogels, incorporating ammonium alginate, were fabricated via a convenient and eco-friendly freeze drying method. It is significant to understand rheological properties of precursor gels because they directly affect the form of aerogels and [...] Read more.
A series of low density, highly porous clay/poly(vinyl alcohol) composite aerogels, incorporating ammonium alginate, were fabricated via a convenient and eco-friendly freeze drying method. It is significant to understand rheological properties of precursor gels because they directly affect the form of aerogels and their processing behaviors. The introduction of ammonium alginate impacted the rheological properties of colloidal gels and improved the mechanical performance of the subject aerogels. The specific compositions and processing conditions applied to those colloidal gel systems brought about different aerogel morphologies, which in turn translated into the observed mechanical properties. The bridge between gel rheologies and aerogel structures are established in the present work. Full article
(This article belongs to the Special Issue Aerogels 2018)
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9 pages, 775 KiB  
Article
Densification and Strengthening of Aerogels by Sintering Heat Treatments or Plastic Compression
by Thierry Woignier and Laurent Duffours
Gels 2018, 4(1), 12; https://doi.org/10.3390/gels4010012 - 31 Jan 2018
Cited by 14 | Viewed by 3831
Abstract
Due to their broad range of porosity, aerogels are suited to various applications. The advantages of a broad range of porosity are used directly, for example, in thermal and acoustic insulation, as materials for space applications or in catalysers. However, an overly high [...] Read more.
Due to their broad range of porosity, aerogels are suited to various applications. The advantages of a broad range of porosity are used directly, for example, in thermal and acoustic insulation, as materials for space applications or in catalysers. However, an overly high pore volume can also be a drawback, for example, in a glass precursor and host matrix. Fortunately, aerogel porosity can be tailored using sintering or isostatic compression. Sets of silica aerogels—sintered and compressed aerogels—have been studied with the objective of comparing these different densification mechanisms. We focus on the mechanical changes during the two processes of densification. Full article
(This article belongs to the Special Issue Aerogels 2018)
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15 pages, 8712 KiB  
Article
Clay-Facilitated Aqueous Dispersion of Graphite and Poly(vinyl alcohol) Aerogels Filled with Binary Nanofillers
by Lei Liu, Yuxin Wang, Saeed M. Alhassan, Hua Sun, Kyungwho Choi, Choongho Yu and David A. Schiraldi
Gels 2018, 4(1), 8; https://doi.org/10.3390/gels4010008 - 12 Jan 2018
Cited by 9 | Viewed by 4390
Abstract
Dispersion of graphite in water was achieved using clay as dispersing aid. In the absence of polymer, the clay/graphite suspensions were sufficiently stable to produce aerogels composed of very thin layers of uniformly dispersed nanoparticles. Poly(vinyl alcohol) (PVOH) aerogels containing binary nanofillers (clay [...] Read more.
Dispersion of graphite in water was achieved using clay as dispersing aid. In the absence of polymer, the clay/graphite suspensions were sufficiently stable to produce aerogels composed of very thin layers of uniformly dispersed nanoparticles. Poly(vinyl alcohol) (PVOH) aerogels containing binary nanofillers (clay plus graphite) were then fabricated and tested. These composites were found to maintain low thermal and electrical conductivities even with high loading of graphite. A unique compressive stress-strain behavior was observed for the aerogel, exhibiting a plateau in the densification region, likely due to sliding between clay and graphite layers within the PVOH matrix. The aerogels containing only graphite exhibited higher compressive modulus, yield stress and toughness values than the samples filled with binary nanofillers. X-ray diffraction (XRD) spectra for the same composite aerogel before and after compression testing illustrated the compression-induced dispersion changes of nanofillers. Composites containing 50 wt % graphite demonstrated a downshift of its 2D Raman peak implying graphite exfoliation to graphene with less than 5 layers. Full article
(This article belongs to the Special Issue Aerogels 2018)
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13 pages, 3673 KiB  
Article
Enhancement Studies on Manufacturing and Properties of Novel Silica Aerogel Composites
by Sunil Chandrakant Joshi, Periyasamy Manikandan and Yogeswari Jothi
Gels 2018, 4(1), 5; https://doi.org/10.3390/gels4010005 - 7 Jan 2018
Cited by 9 | Viewed by 5536
Abstract
Silica Aerogel composites are ultra-low density, highly porous foam-like materials that exhibit excellent thermal insulation and high strain recovery characteristics. In the present work, environment-friendly silica aerogel composites are fabricated using silica aerogel granules with bio based porcine-gelatin as the binding agent dissolved [...] Read more.
Silica Aerogel composites are ultra-low density, highly porous foam-like materials that exhibit excellent thermal insulation and high strain recovery characteristics. In the present work, environment-friendly silica aerogel composites are fabricated using silica aerogel granules with bio based porcine-gelatin as the binding agent dissolved in water and by further drying the mix at sub-zero condition. This article focuses on improvement studies carried on the mold design and the manufacturing process to achieve better geometric compliance for the silica aerogel composites. It also presents contact angle measurements, compressive behavior under different cycles of loading, time dependent behavior and flexural response of the composites. The influence of additives, such as fumed silica and carbon nanotubes on mechanical properties of the composites is also deliberated. Water droplet contact angle experiments confirmed the ultra-hydrophobic nature of the composites. The mechanical properties were characterized under cyclic loading-unloading compression and three-point flexure tests. On successive compression in three consecutive load cycles, the strain and thickness recovery were found to decrease by around 30%. The flexural properties of the aerogel composites were investigated using it as the core covered by thin carbon composite face sheets. It was found that the flexural strength and the failure strain of this aerogel sandwich composites is approximately half of the conventional nomex honeycomb sandwich equivalent. Full article
(This article belongs to the Special Issue Aerogels 2018)
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Review

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14 pages, 5179 KiB  
Review
Non-Conventional Methods for Gelation of Alginate
by Pavel Gurikov and Irina Smirnova
Gels 2018, 4(1), 14; https://doi.org/10.3390/gels4010014 - 1 Feb 2018
Cited by 100 | Viewed by 11853
Abstract
This review presents and critically evaluates recent advances in non-conventional gelation method of native alginate. A special focus is given to the following three methods: cryotropic gelation, non-solvent induced phase separation and carbon dioxide induced gelation. A few other gelation approaches are also [...] Read more.
This review presents and critically evaluates recent advances in non-conventional gelation method of native alginate. A special focus is given to the following three methods: cryotropic gelation, non-solvent induced phase separation and carbon dioxide induced gelation. A few other gelation approaches are also briefly reviewed. Results are discussed in the context of subsequent freeze and supercritical drying. The methods are selected so as to provide the readers with a range of novel tools and tactics of pore engineering for alginate and other anionic polysaccharides. Full article
(This article belongs to the Special Issue Aerogels 2018)
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5083 KiB  
Review
Kinetics of Supercritical Drying of Gels
by İbrahim Şahin, Yaprak Özbakır, Zeynep İnönü, Zeynep Ulker and Can Erkey
Gels 2018, 4(1), 3; https://doi.org/10.3390/gels4010003 - 29 Dec 2017
Cited by 97 | Viewed by 12503
Abstract
Supercritical drying of gels is considered as the most important step of aerogel production since it enables preservation of the three-dimensional pore structure which lead to unique material properties such as high porosity, low density, and large surface area. An understanding of the [...] Read more.
Supercritical drying of gels is considered as the most important step of aerogel production since it enables preservation of the three-dimensional pore structure which lead to unique material properties such as high porosity, low density, and large surface area. An understanding of the kinetics of supercritical drying is necessary to provide insight into material development, scale-up, and optimization of the aerogel manufacturing process. Thus, investigation of supercritical drying is gaining increased attention in recent years. This review paper covers the experimental considerations and techniques to study the kinetics of supercritical drying, fundamental mass transfer mechanisms during the drying process and modeling efforts to predict the drying kinetics for varying operating conditions and gel properties. Transport phenomena involving diffusion, convection, spillage by volume expansion, and axial dispersion are discussed by providing the fundamental equations and empirical correlations to predict transfer coefficients. A detailed review of literature covering experimental and theoretical studies on kinetics of supercritical drying is presented. Full article
(This article belongs to the Special Issue Aerogels 2018)
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