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Gels
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Aerogels
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Aerogels

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

Deadline for manuscript submissions: closed (25 October 2015) | Viewed by 51674

Special Issue Editors

Dr. Francoise Quignard

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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
Dr. Nathalie Tanchoux

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 well know, 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. Françoise 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 submissions that pass pre-check are 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 monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). 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 (6 papers)

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Research

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5978 KiB  
Article
Effect of Granule Sizes on Acoustic Properties of Protein-Based Silica Aerogel Composites via Novel Inferential Transmission Loss Method
by Mahesh Sachithanadam and Sunil C. Joshi
Gels 2016, 2(1), 11; https://doi.org/10.3390/gels2010011 - 9 Mar 2016
Cited by 19 | Viewed by 6483
Abstract
The acoustic properties of the silica aerogel (SA) granules of various sizes from 0.50 to 3.35 mm, distributed into six groups of nominal sizes and measured via a two-microphone impedance tube, are presented. The absorption coefficients of the SA granules were evaluated at [...] Read more.
The acoustic properties of the silica aerogel (SA) granules of various sizes from 0.50 to 3.35 mm, distributed into six groups of nominal sizes and measured via a two-microphone impedance tube, are presented. The absorption coefficients of the SA granules were evaluated at ultra- to super-low frequency range from 50–1600 Hz. It was observed that nominal SA granules with sizes of 1.2 mm (AG2) and 1.7 mm (AG3) displayed the best absorption coefficients. When tested with granules filled at 5 cm depth, AG2 and AG3 absorption coefficients peaked at 980 Hz with values of 0.86 and 0.81, respectively. A novel approach to measure transmission loss (TL) by using “inferential” principle is presented. This novel method, named “Inferential Transmission Loss Method” (InTLM), revealed that the average TL, TLavg for both AG2 and AG3 SA granules was 14.83 dB and 15.35 dB, respectively. Gelatin silica aerogels doped with sodium dodecyl sulfate (GSA–SDS) composites comprising of 1.2 mm (GSA–AG2) and 1.7 mm (GSA–AG3) granules of various configurations were fabricated and evaluated for absorption coefficients and TL with known traditional acoustic panels. The results showed that GSA–AG3 had a better absorption coefficient over other configurations for the same corresponding thickness reaching the peak of 0.6 from 1300 to 1450 Hz with TLavg between 10.7 and 20.3 decibels. The four-layered GSA–AG2 and GSA–AG3 composites showed exceptionally high absorption from 500 to 800 Hz suitable for narrow band applications. Lastly, the “InTLM” was matched with the sound meter measurements, with high accuracy between 0.3 and 3.2 dB for low-frequency testing (50–1600 Hz). Full article
(This article belongs to the Special Issue Aerogels)
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3329 KiB  
Article
Synthesis of Porous and Mechanically Compliant Carbon Aerogels Using Conductive and Structural Additives
by Carlos Macias, Gloria Rasines, Tomas E. García, María C. Zafra, Pedro Lavela, José L. Tirado and Conchi O. Ania
Gels 2016, 2(1), 4; https://doi.org/10.3390/gels2010004 - 15 Jan 2016
Cited by 17 | Viewed by 6187
Abstract
We report the synthesis of conductive and mechanically compliant monolithic carbon aerogels prepared by sol-gel polycondensation of melamine-resorcinol-formaldehyde (MRF) mixtures by incorporating diatomite and carbon black additives. The resulting aerogels composites displayed a well-developed porous structure, confirming that the polymerization of the precursors [...] Read more.
We report the synthesis of conductive and mechanically compliant monolithic carbon aerogels prepared by sol-gel polycondensation of melamine-resorcinol-formaldehyde (MRF) mixtures by incorporating diatomite and carbon black additives. The resulting aerogels composites displayed a well-developed porous structure, confirming that the polymerization of the precursors is not impeded in the presence of either additive. The aerogels retained the porous structure after etching off the siliceous additive, indicating adequate cross-linking of the MRF reactants. However, the presence of diatomite caused a significant fall in the pore volumes, accompanied by coarsening of the average pore size (predominance of large mesopores and macropores). The diatomite also prevented structural shrinkage and deformation of the as-prepared monoliths upon densification by carbonization, even after removal of the siliceous framework. The rigid pristine aerogels became more flexible upon incorporation of the diatomite, favoring implementation of binderless monolithic aerogel electrodes. Full article
(This article belongs to the Special Issue Aerogels)
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7030 KiB  
Article
From Fragile to Resilient Insulation: Synthesis and Characterization of Aramid-Honeycomb Reinforced Silica Aerogel Composite Materials
by Marina Schwan, Matthias Rößler, Barbara Milow and Lorenz Ratke
Gels 2016, 2(1), 1; https://doi.org/10.3390/gels2010001 - 22 Dec 2015
Cited by 15 | Viewed by 8953
Abstract
The production of a new composite material embedding aramid honeycomb materials into nano-porous silica aerogels is studied. Our aim is to improve the poor mechanical strength of silica aerogels by aramid honeycombs without losing the amazing properties of the aerogels like little density [...] Read more.
The production of a new composite material embedding aramid honeycomb materials into nano-porous silica aerogels is studied. Our aim is to improve the poor mechanical strength of silica aerogels by aramid honeycombs without losing the amazing properties of the aerogels like little density and low thermal conductivity. The composite materials were prepared using two formulations of silica aerogels in combination with aramid honeycomb materials of different cell sizes. The silica aerogels are prepared using silicon alkoxides methyltrimethoxysilane and tetraethylorthosilicate as precursors in a two-step acid–base sol–gel process. Shortly in advance of the gelation point, the aramid honeycombs were fluted by the sol, gelation occurred and, after the aging process, the gel bodies were supercritically dried. The properties of the received composite materials are satisfying. Even the thermal conductivities and the densities are a bit higher than for pure aerogels. Most importantly, the mechanical strength is improved by a factor of 2.3 compared to aramid honeycomb materials and by a factor of 10 compared to the two silica aerogels themselves. The composite materials have a good prospective to be used as an impressive insulation material. Full article
(This article belongs to the Special Issue Aerogels)
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2845 KiB  
Article
On the Road to Biopolymer Aerogels—Dealing with the Solvent
by Raman Subrahmanyam, Pavel Gurikov, Paul Dieringer, Miaotian Sun and Irina Smirnova
Gels 2015, 1(2), 291-313; https://doi.org/10.3390/gels1020291 - 21 Dec 2015
Cited by 83 | Viewed by 12503 | Correction
Abstract
Aerogels are three-dimensional ultra-light porous structures whose characteristics make them exciting candidates for research, development and commercialization leading to a broad scope of applications ranging from insulation and catalysis to regenerative medicine and pharmaceuticals. Biopolymers have recently entered the aerogel foray. In order [...] Read more.
Aerogels are three-dimensional ultra-light porous structures whose characteristics make them exciting candidates for research, development and commercialization leading to a broad scope of applications ranging from insulation and catalysis to regenerative medicine and pharmaceuticals. Biopolymers have recently entered the aerogel foray. In order to fully realize their potential, progressive strategies dealing with production times and costs reduction must be put in place to facilitate the scale up of aerogel production from lab to commercial scale. The necessity of studying solvent/matrix interactions during solvent exchange and supercritical CO2 drying is presented in this study using calcium alginate as a model system. Four frameworks, namely (a) solvent selection methodology based on solvent/polymer interaction; (b) concentration gradient influence during solvent exchange; (c) solvent exchange kinetics based on pseudo second order model; and (d) minimum solvent concentration requirements for supercritical CO2 drying, are suggested that could help assess the role of the solvent in biopolymer aerogel production. Full article
(This article belongs to the Special Issue Aerogels)
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4123 KiB  
Article
On the Size Effect of Gelation Kinetics in RF Aerogels
by Lorenz Ratke and Anna Hajduk
Gels 2015, 1(2), 276-290; https://doi.org/10.3390/gels1020276 - 10 Dec 2015
Cited by 6 | Viewed by 4361
Abstract
We experimentally and theoretically investigate the size effect of gelation using Resorcinol-Formaldehyde aerogels. We find a clear dependence of gelation time on the sample size under mild shear conditions. We developed a theoretical model based on Smoluchowski’s aggregation model adding, however, a growth [...] Read more.
We experimentally and theoretically investigate the size effect of gelation using Resorcinol-Formaldehyde aerogels. We find a clear dependence of gelation time on the sample size under mild shear conditions. We developed a theoretical model based on Smoluchowski’s aggregation model adding, however, a growth term which accounts for the continuous growth of the colloidal particles while clustering happens. The model is solved analytically and agrees with our experimental observations for base catalyzed RF-gels. Full article
(This article belongs to the Special Issue Aerogels)
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Review

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1039 KiB  
Review
Mechanical Properties and Brittle Behavior of Silica Aerogels
by Thierry Woignier, Juan Primera, Adil Alaoui, Pascal Etienne, Florence Despestis and Sylvie Calas-Etienne
Gels 2015, 1(2), 256-275; https://doi.org/10.3390/gels1020256 - 10 Dec 2015
Cited by 67 | Viewed by 12020
Abstract
Sets of silica gels: aerogels, xerogels and sintered aerogels, have been studied in the objective to understand the mechanical behavior of these highly porous solids. The mechanical behaviour of gels is described in terms of elastic and brittle materials, like glasses or ceramics. [...] Read more.
Sets of silica gels: aerogels, xerogels and sintered aerogels, have been studied in the objective to understand the mechanical behavior of these highly porous solids. The mechanical behaviour of gels is described in terms of elastic and brittle materials, like glasses or ceramics. The magnitude of the elastic and rupture modulus is several orders of magnitude lower compared to dense glass. The mechanical behaviours (elastic and brittle) are related to the same kinds of gel characteristics: pore volume, silanol content and pore size. Elastic modulus depends strongly on the volume fraction of pores and on the condensation reaction between silanols. Concerning the brittleness features: rupture modulus and toughness, it is shown that pores size plays an important role. Pores can be considered as flaws in the terms of fracture mechanics and the flaw size is related to the pore size. Weibull’s theory is used to show the statistical nature of flaw. Moreover, stress corrosion behaviour is studied as a function of environmental conditions (water and alcoholic atmosphere) and temperature. Full article
(This article belongs to the Special Issue Aerogels)
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