Special Issue "Aerogels: Synthesis, Characterization and Application"

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: closed (30 October 2018).

Special Issue Editor

Dr. Barbara Milow
E-Mail Website
Guest Editor
Institute of Materials Research, German Aerospace Center, Cologne, Germany
Interests: aerogels and aerogel based composites development for applications, defined open porous nanostructured materials, multi-functionality and properties adjustment

Special Issue Information

Dear Colleagues and Friends,

The Special Issue, “Aerogels – Synthesis, Characterization and Application”, will focus on the specific development of aerogels and aerogel based composites for advanced applications. Due to the outstanding combination of properties an awesome variety of applications using aerogels and aerogel based composites is possible. Applications requiring materials for thermal super insulation, light weight construction, electrochemical topics, acoustic damping, adsorption agents, medical issues, as well as cosmetics and personal care products to mention some are under development. All of them are dealing with special combinations of properties which are meanly defined by the open porous nanostructured network and the great variety of chemical origin of the aerogels. The requirements can be matched by a careful setting up, starting with lab-scale experiments followed by a smooth scaling-up and leading to industrial scale production in the near future. The idea of the special issue is to collect the knowledge of the correlation between the necessities of taking care on chemical precursors and reaction conditions during synthesis and suitable drying methods as well as further functionalization to meet the required combination of properties. In this context we would like to invite you to contribute to this special issue. Both original papers and reviews dealing with synthesis, characterization and prospective applications as well as numerical simulations on the design and functionality of aerogels and aerogel based composites are welcome.

Dr. Barbara Milow
Guest Editor

Manuscript Submission Information

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Keywords

  • Aerogel
  • Aerogel composite
  • sol-gel process
  • pre- or post-functionalization
  • thermal conductivity
  • mechanical strength
  • process parameter
  • porosity
  • specific surface, particle diameter, pore size, pore volume
  • open porous nanostructured network
  • adsorption
  • light weight
  • supercritical drying
  • numerical simulation
  • applications
  • safety
  • health care
  • fire resistance
  • process technology (including measurement and control equipment)
  • upscaling
  • social / future challenges

Published Papers (7 papers)

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Research

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Open AccessArticle
Synthesis and Properties of Silica and Alginate Hybrid Aerogel Particles with Embedded Carbon Nanotubes (CNTs) for Selective Sorption
Materials 2019, 12(1), 52; https://doi.org/10.3390/ma12010052 - 24 Dec 2018
Cited by 1
Abstract
The manuscript describes methods for producing hybrid silica microparticles and hybrid alginate beads with carbon nanotube (CNT) contents up to 4.5 and 30 wt.%, respectively. Silica hybrid aerogel microparticles with embedded nanotubes were obtained using a two-stage sol–gel method with a gelling process [...] Read more.
The manuscript describes methods for producing hybrid silica microparticles and hybrid alginate beads with carbon nanotube (CNT) contents up to 4.5 and 30 wt.%, respectively. Silica hybrid aerogel microparticles with embedded nanotubes were obtained using a two-stage sol–gel method with a gelling process in an oil-emulsion. Alginate hybrid aerogels with embedded nanotubes were obtained using cross-linking reactions. The following methods were used to measure the structural characteristics of obtained materials: nitrogen adsorption porosimetry, scanning electron microscopy (SEM), and others. It is shown that specific surface area and pore volume increase with the increase of CNT content in silica aerogel microparticles. Obtained aerogels were tested as adsorbents for argon–oxygen separation. The alginate hybrid aerogel with 30 wt.% CNT content has the best argon adsorption selectivity. Full article
(This article belongs to the Special Issue Aerogels: Synthesis, Characterization and Application)
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Open AccessArticle
Poly(Urethane-Acrylate) Aerogels via Radical Polymerization of Dendritic Urethane-Acrylate Monomers
Materials 2018, 11(11), 2249; https://doi.org/10.3390/ma11112249 - 12 Nov 2018
Cited by 5
Abstract
The purpose of this work was to investigate the effect of multifunctionality on material properties of synthetic polymer aerogels. For this purpose, we present the synthesis and characterization of monolithic dendritic-type urethane-acrylate monomers based on an aliphatic/flexible (Desmodur N3300), or an aromatic/rigid (Desmodur [...] Read more.
The purpose of this work was to investigate the effect of multifunctionality on material properties of synthetic polymer aerogels. For this purpose, we present the synthesis and characterization of monolithic dendritic-type urethane-acrylate monomers based on an aliphatic/flexible (Desmodur N3300), or an aromatic/rigid (Desmodur RE) triisocyanate core. The terminal acrylate groups (three at the tip of each of the three branches, nine in total) were polymerized with 2,2′-azobis(isobutyronitrile) (AIBN) via free radical chemistry. The resulting wet-gels were dried with supercritical fluid (SCF) CO2. Aerogels were characterized with ATR-FTIR and solid-state 13C NMR. The porous network was probed with N2-sorption and scanning electron microscopy (SEM). The thermal stability of aerogels was studied with thermogravimetric analysis (TGA). Most aerogels were macroporous materials (porosity > 80%), with high thermal stability (up to 300 °C). Aerogels were softer at low monomer concentrations and more rigid at higher concentrations. The material properties were compared with those of analogous aerogels bearing only one acrylate moiety at the tip of each branch and the same cores, and with those of analogous aerogels bearing norbornene instead of acrylate moieties. The nine-terminal acrylate-based monomers of this study caused rapid decrease of the solubility of the growing polymer and made possible aerogels with much smaller particles and much higher surface areas. For the first time, aliphatic/flexible triisocyanate-based materials could be made with similar properties in terms of particle size and surface areas to their aromatic/rigid analogues. Finally, it was found that with monomers with a high number of crosslinkable groups, material properties are determined by multifunctionality and thus aerogels based on 9-acrylate- and 9-norbornene-terminated monomers were similar. Materials with aromatic cores are carbonizable with satisfactory yields (20–30% w/w) to mostly microporous materials (BET surface areas: 640–740 m2 g−1; micropore surface areas: 360–430 m2 g−1). Full article
(This article belongs to the Special Issue Aerogels: Synthesis, Characterization and Application)
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Open AccessArticle
Carbon Dioxide Hydrogenation by Means of Plasmonic Resonance Activation in Silica Aerogel Media
Materials 2018, 11(11), 2134; https://doi.org/10.3390/ma11112134 - 30 Oct 2018
Abstract
Surface Plasmon Resonance can be used to activate zinc oxide/copper catalysts in order to perform the carbon dioxide hydrogenation reaction by means of light energy, avoiding high-temperature processes. The synthesis and impregnation methods have been designed to fill glass microreactors with ZnO/Cu nanoparticles [...] Read more.
Surface Plasmon Resonance can be used to activate zinc oxide/copper catalysts in order to perform the carbon dioxide hydrogenation reaction by means of light energy, avoiding high-temperature processes. The synthesis and impregnation methods have been designed to fill glass microreactors with ZnO/Cu nanoparticles supported on transparent silica aerogels to maximize the light absorbed by the catalyst. A LED device surrounding the glass microreactors provided white light to activate the catalyst homogeneously throughout the reactor. Temperature, pressure, amount of catalyst and gases flow were studied as possible variables to enhance the process trying to maximize CO2 conversion rates, achieving the best results working at high pressures. The use of transparent SiO2 Aerogels as supports for photocatalytic gas phase reactions even under high-pressure conditions is demonstrated. Full article
(This article belongs to the Special Issue Aerogels: Synthesis, Characterization and Application)
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Open AccessArticle
Correlating Synthesis Parameters to Morphological Entities: Predictive Modeling of Biopolymer Aerogels
Materials 2018, 11(9), 1670; https://doi.org/10.3390/ma11091670 - 09 Sep 2018
Cited by 6
Abstract
In the past decade, biopolymer aerogels have gained significant research attention due to their typical properties, such as low density and thermal insulation, which are reinforced with excellent biocompatibility, biodegradability, and ease of functionalization. Mechanical properties of these aerogels play an important role [...] Read more.
In the past decade, biopolymer aerogels have gained significant research attention due to their typical properties, such as low density and thermal insulation, which are reinforced with excellent biocompatibility, biodegradability, and ease of functionalization. Mechanical properties of these aerogels play an important role in several applications and should be evaluated based on synthesis parameters. To this end, preparation and characterization of polysaccharide-based aerogels, such as pectin, cellulose and k-carrageenan, is first discussed. An interrelationship between their synthesis parameters and morphological entities is established. Such aerogels are usually characterized by a cellular morphology, and under compression undergo large deformations. Therefore, a nonlinear constitutive model is proposed based on large deflections in microcell walls of the aerogel network. Different sizes of the microcells within the network are identified via nitrogen desorption isotherms. Damage is initiated upon pore collapse, which is shown to result from the failure of the microcell wall fibrils. Finally, the model predictions are validated against experimental data of pectin, cellulose, and k-carrageenan aerogels. Given the micromechanical nature of the model, a clear correlation—qualitative and quantitative—between synthesis parameters and the model parameters is also substantiated. The proposed model is shown to be useful in tailoring the mechanical properties of biopolymer aerogels subject to changes in synthesis parameters. Full article
(This article belongs to the Special Issue Aerogels: Synthesis, Characterization and Application)
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Open AccessArticle
Polysaccharide-Based Aerogel Bead Production via Jet Cutting Method
Materials 2018, 11(8), 1287; https://doi.org/10.3390/ma11081287 - 25 Jul 2018
Cited by 9
Abstract
The aim of this work is to develop a method to produce spherical biopolymer-based aerogel particles, which is capable for scale-up in the future. Therefore, the jet cutting method is suggested. Amidated pectin, sodium alginate, and chitosan are used as a precursor (a [...] Read more.
The aim of this work is to develop a method to produce spherical biopolymer-based aerogel particles, which is capable for scale-up in the future. Therefore, the jet cutting method is suggested. Amidated pectin, sodium alginate, and chitosan are used as a precursor (a 1–3 wt. % solution) for particle production via jet cutting. Gelation is realized via two methods: the internal setting method (using calcium carbonate particles as cross-linkers and citric and acidic acid for pH adjustment) and the diffusion method (in calcium chloride solutions). Gel particles are subjected to solvent exchange to ethanol and consequent supercritical drying with CO2. Spherical aerogel particles with narrow particle size distributions in the range of 400 to 1500 µm and a specific surface area of around 500 m2/g are produced. Overall, it can be concluded that the jet cutting method is suitable for aerogel particle production, although the shape of the particles is not perfectly spherical in all cases. However, parameter adjustment might lead to even better shaped particles in further work. Moreover, the biopolymer-based aerogel particles synthesized in this study are tested as humidity absorbers in drying units for home appliances, particularly for dishwashers. It has been shown that for several cycles of absorption and desorption of humidity, aerogel particles are stable with an absorption capacity of around 20 wt. %. Full article
(This article belongs to the Special Issue Aerogels: Synthesis, Characterization and Application)
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Open AccessArticle
Poly(Amide-imide) Aerogel Materials Produced via an Ice Templating Process
Materials 2018, 11(2), 233; https://doi.org/10.3390/ma11020233 - 03 Feb 2018
Cited by 2
Abstract
Low density composites of sodium montmorillonite and poly(amide-imide) polymers have been created using an ice templating method, which serves as an alternative to the often-difficult foaming of high temperature/high performance polymers. The starting polymer was received in the poly(amic acid) form which can [...] Read more.
Low density composites of sodium montmorillonite and poly(amide-imide) polymers have been created using an ice templating method, which serves as an alternative to the often-difficult foaming of high temperature/high performance polymers. The starting polymer was received in the poly(amic acid) form which can be cured using heat, into a water insoluble amide-imide copolymer. The resulting materials have densities in the 0.05 g/cm3 range and have excellent mechanical properties. Using a tertiary amine as a processing aid provides for lower viscosity and allows more concentrated polymer solutions to be used. The concentration of the amine relative to the acid groups on the polymer backbone has been found to cause significant difference in the mechanical properties of the dried materials. The synthesis and characterization of low density versions of two poly(amide-imide) polymers and their composites with sodium montmorillonite clay are discussed in the present work. Full article
(This article belongs to the Special Issue Aerogels: Synthesis, Characterization and Application)
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Review

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Open AccessReview
Review on the Production of Polysaccharide Aerogel Particles
Materials 2018, 11(11), 2144; https://doi.org/10.3390/ma11112144 - 31 Oct 2018
Cited by 28
Abstract
A detailed study of the production of polysaccharide aerogel (bio-aerogel) particles from lab to pilot scale is surveyed in this article. An introduction to various droplets techniques available in the market is given and compared with the lab scale production of droplets using [...] Read more.
A detailed study of the production of polysaccharide aerogel (bio-aerogel) particles from lab to pilot scale is surveyed in this article. An introduction to various droplets techniques available in the market is given and compared with the lab scale production of droplets using pipettes and syringes. An overview of the mechanisms of gelation of polysaccharide solutions together with non-solvent induced phase separation option is then discussed in the view of making wet particles. The main steps of particle recovery and solvent exchange are briefly described in order to pass through the final drying process. Various drying processes are overviewed and the importance of supercritical drying is highlighted. In addition, we present the characterization techniques to analyse the morphology and properties of the aerogels. The case studies of bio-aerogel (agar, alginate, cellulose, chitin, κ-carrageenan, pectin and starch) particles are reviewed. Potential applications of polysaccharide aerogel particles are briefly given. Finally, the conclusions summarize the prospects of the potential scale-up methods for producing bio-aerogel particles. Full article
(This article belongs to the Special Issue Aerogels: Synthesis, Characterization and Application)
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