Special Issue "Aerogels 2018"

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

Deadline for manuscript submissions: 27 May 2018

Special Issue Editors

Guest Editor
Dr. Francoise Quignard

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
Website | E-Mail
Interests: polysaccharides; aerogel; textural properties; self-assembly; chemical modification; catalysis; medical devices
Guest Editor
Dr. Nathalie Tanchoux

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
Website | E-Mail

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

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Gels is an international peer-reviewed open access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) is waived for well-prepared manuscripts submitted to this issue. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

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

Published Papers (7 papers)

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Research

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Open AccessArticle Advanced Recycled Polyethylene Terephthalate Aerogels from Plastic Waste for Acoustic and Thermal Insulation Applications
Received: 18 April 2018 / Revised: 11 May 2018 / Accepted: 14 May 2018 / Published: 17 May 2018
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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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Open AccessArticle The Relation between the Rheological Properties of Gels and the Mechanical Properties of Their Corresponding Aerogels
Received: 7 March 2018 / Revised: 2 April 2018 / Accepted: 3 April 2018 / Published: 9 April 2018
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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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Open AccessArticle Densification and Strengthening of Aerogels by Sintering Heat Treatments or Plastic Compression
Received: 4 January 2018 / Revised: 18 January 2018 / Accepted: 24 January 2018 / Published: 31 January 2018
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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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Open AccessArticle Clay-Facilitated Aqueous Dispersion of Graphite and Poly(vinyl alcohol) Aerogels Filled with Binary Nanofillers
Received: 10 October 2017 / Revised: 20 December 2017 / Accepted: 4 January 2018 / Published: 12 January 2018
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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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Open AccessArticle Enhancement Studies on Manufacturing and Properties of Novel Silica Aerogel Composites
Received: 29 November 2017 / Revised: 2 January 2018 / Accepted: 5 January 2018 / Published: 7 January 2018
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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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Open AccessReview Non-Conventional Methods for Gelation of Alginate
Received: 22 December 2017 / Revised: 25 January 2018 / Accepted: 26 January 2018 / Published: 1 February 2018
Cited by 1 | PDF Full-text (5179 KB) | HTML Full-text | XML Full-text
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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Open AccessReview Kinetics of Supercritical Drying of Gels
Received: 7 December 2017 / Revised: 26 December 2017 / Accepted: 27 December 2017 / Published: 29 December 2017
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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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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Developing Aerogel Surfaces via Switchable-Hydrophilicity Tertiary Amidine Coating for Improved Oil Recovery
Authors: Osman Karatum 1, Stephen A. Steiner III 2 and Desiree L. Plata 1,3 
Affiliations:
1 Department of Civil and Environmental Engineering, Hudson Hall, Duke University, Durham, NC 27707, USA 2 Aerogel Technologies, LLC, Boston, MA 02127, USA
3 Department of Chemical and Environmental Engineering, Mason Laboratory, Yale University, New Haven, CT 06511, USA
Abstract: Blanket aerogels (i.e., Cabot™ Thermal Wrap® (TW) and Aspen™ Spaceloft® (SL)) with surfaces that have controllable wettability are promising advanced materials for oil recovery applications, where high oil uptake during deployment could be coupled with high oil release to enable reusability of recovered oil.The study presented here details the preparation of CO2-switchable blanket aerogel surfaces through the synthesis and application of switchable-hydrophilicity tertiary amidine (i.e., tributylpentanamidine (TBPA)) onto aerogel blanket surfaces using drop casting, dip coating, and physical vapor deposition (PVD) techniques. The structure of the synthesized TBPA verified with 1H NMR, 13C NMR, and mass spectroscopy was and the deposition of TBPA was confirmed by X-ray photoelectron spectroscopy (XPS). Water contact angles on modified aerogel blanket surfaces in air and under a CO2 and water vapor were determined to identify hydrophobic-hydrophilic switchability. Our experiments revealed that surface coating of TBPA onto aerogel blankets was partially successful within limited set of process conditions (e.g., 290 ppm CO2 and 5500 ppm humidity for PVD, 106 ppm CO2 and 700 ppm humidity for drop casting and dip coating), but that the post-aerogel curing modification strategies yielded poor, heterogeneous reproducibility. Overall, more than 40 samples were tested for their switchability from hydrophobic to hydrophilic in the presence of CO2 and water vapor, respectively, and the success rate was 6.25, 11.7 and 18% for PVD, drop casting, and dip coating, respectively. The most likely reasons for unsuccessful coating onto aerogel surfaces are: (1) the heterogeneous fiber structure of the aerogel blankets, which is comprised of not only pure silica aerogel particles but also a mixture of polyester and/or fiberglass and (2) poor distribution of the chemical modifier TBPA over the aerogel blanket surface (i.e., poor coverage). Nevertheless, when successful, the aerogel hydrophobic-hydrophilic switchability produced the desired chemical behavior that should enhance oil recovery. These results indicate that pre-curing aerogel modification strategies, rather than post-curing depositional strategies, would improve the distribution and attachment of TBPA to the aerogel surfaces and enhance the performance of advanced aerogels for oil recovery operations.

 

Title: Prevention of aggregation of nanoparticles during the synthesis of nanogold-containing silica aerogels
Authors: István Lázár* and Hanna J. Szabó
Affiliations: Department of Inorganic and Analytical Chemistry, University of Debrecen, Egyetem tér 1, Debrecen, Hungary, H-4032, e-mail: lazar@science.unideb.hu
Abstract: Nanogold is widely used in many areas of physics and chemistry due to its environment-sensitive plasmon resonance absorption. Immobilization of gold nanoparticles in highly porous silica aerogel offers an attractive alternative over liquid gold solutions as they show a mechanically stable structure, are permeable to gases and can be used even at elevated temperatures. We have found that the commercially available, citrate-stabilized 10 nm gold nanoparticles may suffer aggregation prior to or under the base-catalyzed gelation process of tetramethoxy silane. In the wet gels, Au particles showed increased sizes, changed shapes and 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 occurring in the aerogel setting and 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, dimethyl sulfoxide, dimethyl formamide, and urea changed the shape of nanoparticles converting to rod-like shapes, while diols led to an increase in both size and shape. However, using the polymeric stabilizer poly(vinyl pyrrolidone) efficiently prevented aggregation of the particles even in the presence of high concentration of carbon dioxide and allowed production of nanoAu containing silica aerogels in a single step, without modification of the technology.

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