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Gels
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Aerogels 2020
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Aerogels 2020

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

Deadline for manuscript submissions: closed (30 November 2020) | Viewed by 29834

Special Issue Editors

Dr. Nathalie Tanchoux

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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
Special Issues, Collections and Topics in MDPI journals
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

Special Issue Information

Dear Colleagues,

As you know well, “aerogel” is a broad term used for a special class of ultralight 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 Editor

Manuscript Submission Information

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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 2100 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

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Published Papers (7 papers)

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Research

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17 pages, 42265 KiB  
Article
Durability of Thermal Renders with Lightweight and Thermal Insulating Aggregates: Regranulated Expanded Cork, Silica Aerogel and Expanded Polystyrene
by André Morgado, António Soares, Inês Flores-Colen, Maria do Rosário Veiga and Maria Glória Gomes
Gels 2021, 7(2), 35; https://doi.org/10.3390/gels7020035 - 25 Mar 2021
Cited by 12 | Viewed by 3382
Abstract
Following the trend of energy-efficient construction, renders with thermal insulation properties have been studied for replacing conventional renders. However, there are still few studies on the durability of these renders that may become a barrier for their implementation. In this study, the performance [...] Read more.
Following the trend of energy-efficient construction, renders with thermal insulation properties have been studied for replacing conventional renders. However, there are still few studies on the durability of these renders that may become a barrier for their implementation. In this study, the performance of lightweight renders for thermal insulation to accelerated aging cycles and freeze/thaw cycles is discussed. For this purpose, renders with regranulated expanded cork (GEC), silica aerogel (SA), and expanded polystyrene (EPS) were produced and tested for compressive strength, ultra-sound velocity, Young’s modulus, and thermal conductivity before and after accelerated aging cycles (hygrothermal, IR and freeze/thaw cycles). With this study, a comparison between the influence of different aggregates on renders is carried out in order to understand their effect on different properties of renders. Full article
(This article belongs to the Special Issue Aerogels 2020)
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13 pages, 3630 KiB  
Article
Evaluation of Polyurea-Crosslinked Alginate Aerogels for Seawater Decontamination
by Patrina Paraskevopoulou, Grigorios Raptopoulos, Faidra Leontaridou, Maria Papastergiou, Aikaterini Sakellari and Sotirios Karavoltsos
Gels 2021, 7(1), 27; https://doi.org/10.3390/gels7010027 - 4 Mar 2021
Cited by 15 | Viewed by 4139
Abstract
Polyurea-crosslinked Ca-alginate (X-Ca-alginate) aerogel beads (diameter: 3.3 mm) were evaluated as adsorbents of metal ions, organic solvents, and oils. They were prepared via reaction of an aromatic triisocyanate (Desmodur RE) with pre-formed Ca-alginate wet gels and consisted of 54% polyurea and 2% calcium. [...] Read more.
Polyurea-crosslinked Ca-alginate (X-Ca-alginate) aerogel beads (diameter: 3.3 mm) were evaluated as adsorbents of metal ions, organic solvents, and oils. They were prepared via reaction of an aromatic triisocyanate (Desmodur RE) with pre-formed Ca-alginate wet gels and consisted of 54% polyurea and 2% calcium. X-Ca-alginate aerogels are hydrophobic nanoporous materials (90% v/v porosity), with a high BET surface area (459 m2/g−1), and adsorb PbII not only from ultrapure water (29 mg/g−1) but also from seawater (13 mg/g−1) with high selectivity. The adsorption mechanism involves replacement of CaII by PbII ions coordinated to the carboxylate groups of the alginate backbone. After treatment with a Na2EDTA solution, the beads can be reused, without significant loss of activity for at least two times. X-Ca-alginate aerogels can also uptake organic solvents and oil from seawater; the volume of the adsorbate can be as high as the total pore volume of the aerogel (6.0 mL/g−1), and the absorption is complete within seconds. X-Ca alginate aerogels are suitable for the decontamination of aquatic environments from a broader range of inorganic and organic pollutants. Full article
(This article belongs to the Special Issue Aerogels 2020)
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13 pages, 2143 KiB  
Article
Cellulose Nanofibrils/Xyloglucan Bio-Based Aerogels with Shape Recovery
by Samuel Mandin, Samuel Moreau, Malika Talantikite, Bruno Novalès, Jean-Eudes Maigret, Bernard Cathala and Céline Moreau
Gels 2021, 7(1), 5; https://doi.org/10.3390/gels7010005 - 5 Jan 2021
Cited by 14 | Viewed by 4183
Abstract
Bio-based aerogels containing cellulose nanofibrils (CNFs) are promising materials due to the inherent physical properties of CNF. The high affinity of cellulose to plant hemicelluloses (xyloglucan, xylan, pectin) is also an opportunity to develop biomaterials with new properties. Here, we prepared aerogels from [...] Read more.
Bio-based aerogels containing cellulose nanofibrils (CNFs) are promising materials due to the inherent physical properties of CNF. The high affinity of cellulose to plant hemicelluloses (xyloglucan, xylan, pectin) is also an opportunity to develop biomaterials with new properties. Here, we prepared aerogels from gelled dispersions of CNFs and xyloglucan (XG) at different ratios by using a freeze-casting procedure in unidirectional (UD) and non-directional (ND) manners. As showed by rheology analysis, CNF and CNF/XG dispersions behave as true gels. We investigated the impact of the freezing procedure and the gel’s composition on the microstructure and the water absorption properties. The introduction of XG greatly affects the microstructure of the aerogel from lamellar to cellular morphology. Bio-based aerogels showed high water absorption capacity with shape recovery after compression. The relation between morphology and aerogel compositions is discussed. Full article
(This article belongs to the Special Issue Aerogels 2020)
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16 pages, 3659 KiB  
Article
Investigation of Aerogel Production Processes: Solvent Exchange under High Pressure Combined with Supercritical Drying in One Apparatus
by Artem Lebedev, Ekaterina Suslova, Aleksander Troyankin and Daria Lovskaya
Gels 2021, 7(1), 4; https://doi.org/10.3390/gels7010004 - 5 Jan 2021
Cited by 13 | Viewed by 3944
Abstract
This work aims to contribute to the theoretical and experimental research of supercritical processes for intensification and combination in one apparatus. Investigation is carried out to improve production technology of organic alginate aerogels. It is proposed within the investigation to carry out the [...] Read more.
This work aims to contribute to the theoretical and experimental research of supercritical processes for intensification and combination in one apparatus. Investigation is carried out to improve production technology of organic alginate aerogels. It is proposed within the investigation to carry out the solvent exchange stage, an important stage of organic aerogels production, under pressure in a carbon dioxide medium in the same apparatus used for supercritical drying. The phase behavior in the system “carbon dioxide–water–2-propanol”, which arises during such a solvent exchange stage, is studied theoretically. An experimental study of the process of step-by-step solvent exchange under pressure was carried out through multiphase and homogeneous regions of the phase diagram of such a system. As a result, new highly efficient technology for the production of organic aerogels was proposed, which can be implemented by combining the two main stages of the process. Full article
(This article belongs to the Special Issue Aerogels 2020)
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12 pages, 3906 KiB  
Article
Starch-Based Aerogels Obtained via Solvent-Induced Gelation
by Mirelle Dogenski, Pavel Gurikov, Victor Baudron, J. Vladimir de Oliveira, Irina Smirnova and Sandra R. S. Ferreira
Gels 2020, 6(3), 32; https://doi.org/10.3390/gels6030032 - 19 Sep 2020
Cited by 10 | Viewed by 5543
Abstract
In this work, the ability of several solvents to induce gel formation from amylomaize starch solubilized in dimethyl sulfoxide (DMSO) was investigated. The formed gels were subjected to solvent exchange using ethanol and dried with supercritical carbon dioxide (sc-CO2) to obtain [...] Read more.
In this work, the ability of several solvents to induce gel formation from amylomaize starch solubilized in dimethyl sulfoxide (DMSO) was investigated. The formed gels were subjected to solvent exchange using ethanol and dried with supercritical carbon dioxide (sc-CO2) to obtain the aerogels. The influence of starch concentration (3–15 wt%) and solvent content (20–80 wt%) on gel formation was also studied. It was demonstrated that the gelation of starch in binary mixtures of solvents can be rationalized by Hansen Solubility Parameters (HSP) revealing a crucial hole of hydrogen bonding for the gel’s strength, which is in agreement with rheological measurements. Only the addition of water or propylene glycol to starch/DMSO solutions resulted in strong gels at a minimum starch and solvent content of 7.5 wt% and 50 wt%, respectively. The resulting aerogels showed comparably high specific surface areas (78–144 m2 g−1) and low envelope densities (0.097–0.203 g cm−3). The results of this work indicate that the HSP parameters could be used as a tool to guide the rational selection of water-free gelation in starch/DMSO systems. In addition, it opens up an attractive opportunity to perform starch gelation in those solvents that are miscible with sc-CO2, avoiding the time-consuming step of solvent exchange. Full article
(This article belongs to the Special Issue Aerogels 2020)
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16 pages, 6466 KiB  
Article
In Situ Measurement Methods for the CO2-Induced Gelation of Biopolymer Systems
by Imke Preibisch, Lena-Marie Ränger, Pavel Gurikov and Irina Smirnova
Gels 2020, 6(3), 28; https://doi.org/10.3390/gels6030028 - 9 Sep 2020
Cited by 6 | Viewed by 3115
Abstract
This work presents two novel methods to investigate in situ the carbon dioxide (CO2)-induced gelation of biopolymer-based solutions. The CO2-induced gelation is performed in a viewing cell at room temperature under CO2 pressure (20 to 60 bar), whereby [...] Read more.
This work presents two novel methods to investigate in situ the carbon dioxide (CO2)-induced gelation of biopolymer-based solutions. The CO2-induced gelation is performed in a viewing cell at room temperature under CO2 pressure (20 to 60 bar), whereby calcium precursors are used as cross-linkers. The novel methods allow the in situ optical observation and evaluation of the gelation process via the change in turbidity due to dissolution of dispersed calcium carbonate (CaCO3) particles and in situ pH measurements. The combination of both methods enables the determination of the gelation direction, gelation rate, and the pH value in spatial and temporal resolution. The optical gelation front and pH front both propagate equally from top to bottom through the sample solutions, indicating a direct link between a decrease in the pH value and the dissolution of the CaCO3 particles. Close-to-vertical movement of both gelation front and pH front suggests almost one dimensional diffusion of CO2 from the contact surface (gel–CO2) to the bottom of the sample. The gelation rate increases with the increase in CO2 pressure. However, the increase in solution viscosity and the formation of a gel layer result in a strong decrease in the gelation rate due to a hindrance of CO2 diffusion. Released carbonate ions from CaCO3 dissolution directly influence the reaction equilibrium between CO2 and water and therefore the change in pH value of the solution. Increasing the CaCO3 concentrations up to the solubility results in lower gelation rates. Full article
(This article belongs to the Special Issue Aerogels 2020)
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Review

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16 pages, 3355 KiB  
Review
Fractal Structure in Silica and Composites Aerogels
by Thierry Woignier, Juan Primera, Adil Alaoui, Philippe Dieudonne, Laurent Duffours, Isabelle Beurroies, Sylvie Calas-Etienne, Florence Despestis, Annelise Faivre and Pascal Etienne
Gels 2021, 7(1), 1; https://doi.org/10.3390/gels7010001 - 26 Dec 2020
Cited by 18 | Viewed by 4550
Abstract
Silica aerogels are known to be materials with exceptional characteristics, such as ultra-low density, high surface area, high porosity, high adsorption, and low-thermal conductivity. In addition, these unique properties are mainly related to their specific processing. Depending on the aerogel synthesis procedure, the [...] Read more.
Silica aerogels are known to be materials with exceptional characteristics, such as ultra-low density, high surface area, high porosity, high adsorption, and low-thermal conductivity. In addition, these unique properties are mainly related to their specific processing. Depending on the aerogel synthesis procedure, the aerogels texture can be tailored with meso and/or macroporosity. Fractal geometry has been observed and used to describe silica aerogels at nanoscales in certain conditions. In this review paper, we describe the fractal structure of silica aerogels that can develop depending on the synthesis conditions. X-ray and neutron scattering measurements allow to show that silica aerogels can exhibit a fractal structure over one or even more than two orders of magnitude in length. The fractal dimension does not depend directly on the material density but can vary with the synthesis conditions. It ranges typically between 1.6 and 2.4. The effect of the introduction of silica particles or of further thermal treatment or compression of the silica aerogels on their microstructure and their fractal characteristics is also resumed. Full article
(This article belongs to the Special Issue Aerogels 2020)
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