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Wang C, Guo Y, Türel T, Tomović Ž. Fabrication of High-Performance Polyisocyanurate Aerogels through Cocyclotrimerization of 4,4'-Methylene Diphenyl Diisocyanate and Its Mono-Urethane Derivatives. ACS APPLIED MATERIALS & INTERFACES 2024; 16:35604-35612. [PMID: 38920358 PMCID: PMC11247422 DOI: 10.1021/acsami.4c07480] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2024] [Revised: 06/17/2024] [Accepted: 06/18/2024] [Indexed: 06/27/2024]
Abstract
Aromatic polyisocyanurate (PIR) aerogels are recognized as advanced porous materials and extensively studied due to their lightweight nature, high porosity, and specific surface area, which attribute to their outstanding thermal insulation properties. The inherent thermal stability of the PIR moieties, combined with great insulating performance, renders PIR aerogels highly suitable for building insulation applications. Nevertheless, materials containing isocyanurate obtained through direct trimerization of aromatic isocyanates exhibit brittleness, resulting in inferior mechanical performance. In order to enhance the processability of the PIR aerogels, we propose a cocyclotrimerization approach involving mixtures of mono- and difunctional aromatic isocyanates. This approach is designed to develop a PIR network with decreased cross-linking density and brittleness. Herein, we developed an array of PIR aerogels from different alkyl chain-modified isocyanate mixtures. The resulting PIR aerogels exhibited high porosity (>89%), a large surface area (∼300 m2/g), superinsulating performance with ultralow thermal conductivity (∼16.8 mW m-1 K-1), notable thermal stability (Td5% ∼ 250 °C), improved mechanical performance, and intrinsic hydrophobicity without the need for postmodification. These high-performance organic aerogels hold significant promise for applications requiring superinsulating materials.
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Affiliation(s)
- Changlin Wang
- Polymer Performance Materials
Group, Department of Chemical Engineering and Chemistry, Eindhoven University
of Technology, 5600 MB Eindhoven, The Netherlands
| | - Yunfei Guo
- Polymer Performance Materials
Group, Department of Chemical Engineering and Chemistry, Eindhoven University
of Technology, 5600 MB Eindhoven, The Netherlands
| | - Tankut Türel
- Polymer Performance Materials
Group, Department of Chemical Engineering and Chemistry, Eindhoven University
of Technology, 5600 MB Eindhoven, The Netherlands
| | - Željko Tomović
- Polymer Performance Materials
Group, Department of Chemical Engineering and Chemistry, Eindhoven University
of Technology, 5600 MB Eindhoven, The Netherlands
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Pinilla-Peñalver E, Cantero D, Romero A, Sánchez-Silva L. Exploring the Impact of the Synthesis Variables Involved in the Polyurethane Aerogels-like Materials Design. Gels 2024; 10:209. [PMID: 38534627 DOI: 10.3390/gels10030209] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2024] [Revised: 03/13/2024] [Accepted: 03/15/2024] [Indexed: 03/28/2024] Open
Abstract
This research presents a novel approach to synthesising polyurethane (PUR)-based aerogels at the pilot scale, optimizing synthesis variables such as the gelation solvent, solids content, chain extender/isocyanate ratio, and dispersion mode. The solids content (2-11 wt.%) is the parameter with the most influence on the density of the aerogels, with a clear decrease in this property as the solids content decreases. On the other hand, it was demonstrated that minimizing the excess of ethylenediamine (used as chain extender) in relation to the isocyanate is a valuable consideration to improve the thermal conductivity of the aerogel. Related to the chain extender/isocyanate ratio, a compromise situation where the initial isocyanate reacts almost completely is crucial. Fourier-transform infrared spectroscopy was used to conduct such monitoring during the reaction. Once the conditions were optimised, the aerogel showing improved properties was synthesised using ethyl acetate as the gelling solvent, a 3.7 wt.% solids content, an ethylenediamine/isocyanate ratio of 0.20, and sonication as the dispersion mode, attaining a thermal conductivity of 0.030 W m-1 K-1 and a density of 0.046 g cm-3. Therefore, the synthesized aerogel emerges as a promising candidate for use in the construction and automotive industries.
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Affiliation(s)
- Esther Pinilla-Peñalver
- Department of Chemical Engineering, University of Castilla-La Mancha, Avda. Camilo José Cela 12, 13071 Ciudad Real, Spain
| | - Darío Cantero
- Department of Chemical Engineering, University of Castilla-La Mancha, Avda. Camilo José Cela 12, 13071 Ciudad Real, Spain
| | - Amaya Romero
- Department of Chemical Engineering, University of Castilla-La Mancha, Avda. Camilo José Cela 12, 13071 Ciudad Real, Spain
| | - Luz Sánchez-Silva
- Department of Chemical Engineering, University of Castilla-La Mancha, Avda. Camilo José Cela 12, 13071 Ciudad Real, Spain
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Malfait WJ, Ebert HP, Brunner S, Wernery J, Galmarini S, Zhao S, Reichenauer G. The poor reliability of thermal conductivity data in the aerogel literature: a call to action! JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY 2024; 109:569-579. [PMID: 38419740 PMCID: PMC10896818 DOI: 10.1007/s10971-023-06282-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/07/2023] [Accepted: 11/26/2023] [Indexed: 03/02/2024]
Abstract
Aerogels are an exciting class of materials with record-breaking properties including, in some cases, ultra-low thermal conductivities. The last decade has seen a veritable explosion in aerogel research and industry R&D, leading to the synthesis of aerogels from a variety of materials for a rapidly expanding range of applications. However, both from the research side, and certainly from a market perspective, thermal insulation remains the dominant application. Unfortunately, continued progress in this area suffers from the proliferation of incorrect thermal conductivity data, with values that often are far outside of what is possible within the physical limitations. This loss of credibility in reported thermal conductivity data poses difficulties in comparing the thermal performance of different types of aerogels and other thermal superinsulators, may set back further scientific progress, and hinder technology transfer to industry and society. Here, we have compiled 519 thermal conductivity results from 87 research papers, encompassing silica, other inorganic, biopolymer and synthetic polymer aerogels, to highlight the extent of the problem. Thermal conductivity data outside of what is physically possible are common, even in high profile journals and from the world's best universities and institutes. Both steady-state and transient methods can provide accurate thermal conductivity data with proper instrumentation, suitable sample materials and experienced users, but nearly all implausible data derive from transient methods, and hot disk measurements in particular, indicating that under unfavorable circumstances, and in the context of aerogel research, transient methods are more prone to return unreliable data. Guidelines on how to acquire reliable thermal conductivity data are provided. This paper is a call to authors, reviewers, editors and readers to exercise caution and skepticism when they report, publish or interpret thermal conductivity data. Graphical Abstract
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Affiliation(s)
- Wim J. Malfait
- Laboratory for Building Energy Materials and Components, Empa - Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland
| | | | - Samuel Brunner
- Laboratory for Building Energy Materials and Components, Empa - Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland
| | - Jannis Wernery
- Laboratory for Building Energy Materials and Components, Empa - Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland
| | - Sandra Galmarini
- Laboratory for Building Energy Materials and Components, Empa - Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland
| | - Shanyu Zhao
- Laboratory for Building Energy Materials and Components, Empa - Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland
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Payanda Konuk O, Alsuhile AAAM, Yousefzadeh H, Ulker Z, Bozbag SE, García-González CA, Smirnova I, Erkey C. The effect of synthesis conditions and process parameters on aerogel properties. Front Chem 2023; 11:1294520. [PMID: 37937209 PMCID: PMC10627014 DOI: 10.3389/fchem.2023.1294520] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2023] [Accepted: 10/12/2023] [Indexed: 11/09/2023] Open
Abstract
Aerogels are remarkable nanoporous materials with unique properties such as low density, high porosity, high specific surface area, and interconnected pore networks. In addition, their ability to be synthesized from various precursors such as inorganics, organics, or hybrid, and the tunability of their properties make them very attractive for many applications such as adsorption, thermal insulation, catalysts, tissue engineering, and drug delivery. The physical and chemical properties and pore structure of aerogels are crucial in determining their application areas. Moreover, it is possible to tailor the aerogel properties to meet the specific requirements of each application. This review presents a comprehensive review of synthesis conditions and process parameters in tailoring aerogel properties. The effective parameters from the dissolution of the precursor step to the supercritical drying step, including the carbonization process for carbon aerogels, are investigated from the studies reported in the literature.
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Affiliation(s)
- Ozge Payanda Konuk
- Department of Materials Science and Engineering, Koç University, Istanbul, Türkiye
| | - Ala A. A. M. Alsuhile
- Department of Chemical and Biological Engineering, Koç University, Istanbul, Türkiye
| | - Hamed Yousefzadeh
- Department of Chemical Engineering, Yeditepe University, Atasehir, Istanbul, Türkiye
| | - Zeynep Ulker
- School of Pharmacy, Altinbas University, Istanbul, Türkiye
| | - Selmi E. Bozbag
- Department of Chemical and Biological Engineering, Koç University, Istanbul, Türkiye
| | - C. A. García-González
- Departamento de Farmacología, Farmacia Y Tecnología Farmacéutica, I+D Farma (GI-1645), Faculty of Pharmacy, Instituto de Materiales (iMATUS) and Health Research Institute of Santiago de Compostela (IDIS), Universidade de Santiago de Compostela, Santiago de Compostela, Spain
| | - I. Smirnova
- Institute of Thermal Separation Processes, Hamburg University of Technology, Hamburg, Germany
| | - Can Erkey
- Department of Materials Science and Engineering, Koç University, Istanbul, Türkiye
- Department of Chemical and Biological Engineering, Koç University, Istanbul, Türkiye
- Koç University Tüpraş Energy Center (KUTEM), Koç University, Istanbul, Türkiye
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Sivaraman D, Siqueira G, Maurya AK, Zhao S, Koebel MM, Nyström G, Lattuada M, Malfait WJ. Superinsulating nanocellulose aerogels: Effect of density and nanofiber alignment. Carbohydr Polym 2022; 292:119675. [PMID: 35725170 DOI: 10.1016/j.carbpol.2022.119675] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Revised: 05/09/2022] [Accepted: 05/27/2022] [Indexed: 11/30/2022]
Abstract
Cellulose aerogels are potential alternatives to silica aerogels with advantages in cost, sustainability and mechanical properties. However, the density dependence of thermal conductivity (λ) for cellulose aerogels remains controversial. Cellulose aerogels were produced by gas-phase pH induced gelation of TEMPO-oxidized cellulose nanofibers (CNF) and supercritical drying. Their properties are evaluated by varying the CNF concentration (5-33 mg·cm-3) and by uniaxial compression (9-115 mg·cm-3). The aerogels are transparent with specific surface areas of ~400 m2·g-1, mesopore volumes of ~2 cm3·g-1 and a power-law dependence of the E-modulus (α ~ 1.53, and the highest reported E of ~1 MPa). The dataset confirms that λ displays a traditional U-shaped density dependence with a minimum of 18 mW·m-1·K-1 at 0.065 g·cm-3. For a given density, λ is ~5 mW·m-1·K-1 lower for compressed aerogels due to the alignment of nanofibers, confirmed by small angle X-ray scattering (SAXS).
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Affiliation(s)
- Deeptanshu Sivaraman
- Empa - Building Energy Materials and Components, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland; Department of Chemistry, University of Fribourg, Fribourg, Switzerland.
| | - Gilberto Siqueira
- Cellulose & Wood Materials Laboratory, Empa - Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland
| | - Anjani K Maurya
- Empa - Center for X-ray Analytics, Swiss Federal Laboratories for Materials Science and Technology, Empa, St. Gallen, Switzerland
| | - Shanyu Zhao
- Empa - Building Energy Materials and Components, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland
| | - Matthias M Koebel
- Empa - Building Energy Materials and Components, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland
| | - Gustav Nyström
- Cellulose & Wood Materials Laboratory, Empa - Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland; Department of Health Sciences and Technology, ETH Zürich, 8092 Zürich, Switzerland
| | - Marco Lattuada
- Department of Chemistry, University of Fribourg, Fribourg, Switzerland
| | - Wim J Malfait
- Empa - Building Energy Materials and Components, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland
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Jarray A, Feichtinger A, Scholten E. Linking intermolecular interactions and rheological behaviour in capillary suspensions. J Colloid Interface Sci 2022; 627:415-426. [PMID: 35863200 DOI: 10.1016/j.jcis.2022.07.067] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2022] [Revised: 06/20/2022] [Accepted: 07/11/2022] [Indexed: 11/30/2022]
Abstract
HYPOTHESIS Capillary suspensions feature networks of particles connected by liquid bridges, which are obtained by adding a small amount of a second immiscible liquid to a suspension. It is possible to link the network formation as well as the rheological behaviour of capillary suspensions to the intermolecular interactions of their constituents. EXPERIMENTS AND SIMULATIONS Through a combination of experimental and numerical methods, we present a novel approach, based on Hansen solubility parameters computed from Molecular Dynamics (MD) simulations, to rationalize and predict the rheological behaviour of capillary suspensions. We investigated the formation of capillary suspensions for various combinations of bulk and secondary liquids mixed with hydrophilic silica particles. The predictions were confirmed experimentally by rheological analysis, interfacial tension measurements and microscopy (CLSM) imaging. FINDINGS Numerical and experimental results show that the Hansen solubility parameters theory allows to predict the formation of capillary suspensions, whose strength exponentially decays with decreasing intermolecular interactions between the secondary liquids and the dispersed particles. High immiscibility between the bulk and secondary liquid strengthens the gel up to a critical immiscibility point, above which the strength of the gel remains mostly affected by the affinity between the secondary liquids and the dispersed particles. Furthermore, we find that hydrogen-bonding and polar interactions control the formation of capillary suspensions. This simple approach can guide the selection of adequate solvents and immiscible secondary liquids, allowing an easy formulation of new particulate-based gels.
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Affiliation(s)
- Ahmed Jarray
- Physics and Physical Chemistry of Foods, Wageningen University, PO Box 17, 6700 AA Wageningen, the Netherlands; Multi Scale Mechanics (MSM), MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, the Netherlands.
| | - Annika Feichtinger
- Physics and Physical Chemistry of Foods, Wageningen University, PO Box 17, 6700 AA Wageningen, the Netherlands.
| | - Elke Scholten
- Physics and Physical Chemistry of Foods, Wageningen University, PO Box 17, 6700 AA Wageningen, the Netherlands.
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Super-Insulating Transparent Polyisocyanurate-Polyurethane Aerogels: Analysis of Thermal Conductivity and Mechanical Properties. NANOMATERIALS 2022; 12:nano12142409. [PMID: 35889633 PMCID: PMC9320143 DOI: 10.3390/nano12142409] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Revised: 06/25/2022] [Accepted: 07/12/2022] [Indexed: 02/04/2023]
Abstract
A family of transparent polyisocyanurate-polyurethane (PUR-PIR) aerogels with an interesting combination of physical properties were synthesized. First, their textural properties were analyzed aiming to study catalyst influence on the final porous structures and densities. Their thermal conductivities were measured at different temperatures allowing observation of a clear trend relating the initial formulation with the porous structure and reaching values as low as 12 mW/mK, the lowest found in the literature for aerogels based on this polymer matrix. Contributions to thermal conductivity were calculated, improving the understanding of the porous structure-insulating performance relationship. Moreover, their mechanical properties were studied (elastic modulus, stress at different strains and elastic behavior). The aerogels showed tunable stiffness (elastic modulus from 6.32 to 0.13 MPa) by changing the catalyst concentration and significant elasticity. Thus, super-insulating transparent PUR-PIR aerogels with tailored mechanical properties were obtained opening a wide range of potential applications in the energy, building, automotive and aeronautical sectors, among others. The exceptional insulation of silica aerogels was reached at the same time that their general brittleness was improved while keeping good transparency to visible light (85%, 650 nm). Therefore, these aerogels may constitute an alternative to silica aerogels.
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Merillas B, Vareda JP, Martín-de León J, Rodríguez-Pérez MÁ, Durães L. Thermal Conductivity of Nanoporous Materials: Where Is the Limit? Polymers (Basel) 2022; 14:2556. [PMID: 35808603 PMCID: PMC9269606 DOI: 10.3390/polym14132556] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2022] [Revised: 06/14/2022] [Accepted: 06/15/2022] [Indexed: 02/04/2023] Open
Abstract
Nowadays, our society is facing problems related to energy availability. Owing to the energy savings that insulators provide, the search for effective insulating materials is a focus of interest. Since the current insulators do not meet the increasingly strict requirements, developing materials with a greater insulating capacity is needed. Until now, several nanoporous materials have been considered as superinsulators achieving thermal conductivities below that of the air 26 mW/(m K), like nanocellular PMMA/TPU, silica aerogels, and polyurethane aerogels reaching 24.8, 10, and 12 mW/(m K), respectively. In the search for the minimum thermal conductivity, still undiscovered, the first step is understanding heat transfer in nanoporous materials. The main features leading to superinsulation are low density, nanopores, and solid interruptions hindering the phonon transfer. The second crucial condition is obtaining reliable thermal conductivity measurement techniques. This review summarizes these techniques, and data in the literature regarding the structure and thermal conductivity of two nanoporous materials, nanocellular polymers and aerogels. The key conclusion of this analysis specifies that only steady-state methods provide a reliable value for thermal conductivity of superinsulators. Finally, a theoretical discussion is performed providing a detailed background to further explore the lower limit of superinsulation to develop more efficient materials.
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Affiliation(s)
- Beatriz Merillas
- Cellular Materials Laboratory (CellMat), Department of Condensed Material Physics, Facultad de Ciencias, University of Valladolid, 47011 Valladolid, Spain; (B.M.); (J.M.-d.L.); (M.Á.R.-P.)
| | - João Pedro Vareda
- University of Coimbra, Chemical Process Engineering and Forest Products Research Centre, Department of Chemical Engineering, Rua Sílvio Lima, 3030-790 Coimbra, Portugal;
| | - Judith Martín-de León
- Cellular Materials Laboratory (CellMat), Department of Condensed Material Physics, Facultad de Ciencias, University of Valladolid, 47011 Valladolid, Spain; (B.M.); (J.M.-d.L.); (M.Á.R.-P.)
| | - Miguel Ángel Rodríguez-Pérez
- Cellular Materials Laboratory (CellMat), Department of Condensed Material Physics, Facultad de Ciencias, University of Valladolid, 47011 Valladolid, Spain; (B.M.); (J.M.-d.L.); (M.Á.R.-P.)
- BioEcoUVA Research Institute on Bioeconomy, University of Valladolid, 47011 Valladolid, Spain
| | - Luisa Durães
- University of Coimbra, Chemical Process Engineering and Forest Products Research Centre, Department of Chemical Engineering, Rua Sílvio Lima, 3030-790 Coimbra, Portugal;
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Leventis N. Polyurea Aerogels: Synthesis, Material Properties, and Applications. Polymers (Basel) 2022; 14:969. [PMID: 35267798 PMCID: PMC8912528 DOI: 10.3390/polym14050969] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2022] [Revised: 02/23/2022] [Accepted: 02/24/2022] [Indexed: 12/10/2022] Open
Abstract
Polyurea is an isocyanate derivative, and comprises the basis for a well-established class of polymeric aerogels. Polyurea aerogels are prepared either via reaction of multifunctional isocyanates with multifunctional amines, via reaction of multifunctional isocyanates and water, or via reaction of multifunctional isocyanates and mineral acids. The first method is the established one for the synthesis of polyurea, the third is a relatively new method that yields polyurea doped with metal oxides in one step, while the reaction of isocyanates with water has become the most popular route to polyurea aerogels. The intense interest in polyurea aerogels can be attributed in part to the low cost of the starting materials-especially via the water method-in part to the extremely broad array of nanostructural morphologies that allow study of the nanostructure of gels as a function of synthetic conditions, and in part to the broad array of functional properties that can be achieved even within a single chemical composition by simply adjusting the synthetic parameters. In addition, polyurea aerogels based on aromatic isocyanates are typically carbonizable materials, making them highly competitive alternatives to phenolic aerogels as precursors of carbon aerogels. Several types of polyurea aerogels are already at different stages of commercialization. This article is a comprehensive review of all polyurea-based aerogels, including polyurea-crosslinked oxide and biopolymer aerogels, from a fundamental nanostructure-material properties perspective, as well as from an application perspective in thermal and acoustic insulation, oil adsorption, ballistic protection, and environmental cleanup.
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Affiliation(s)
- Nicholas Leventis
- Aspen Aerogels, Inc. 30 Forbes Road, Bldg B, Northborough, MA 01532, USA
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Juhász L, Moldován K, Gurikov P, Liebner F, Fábián I, Kalmár J, Cserháti C. False Morphology of Aerogels Caused by Gold Coating for SEM Imaging. Polymers (Basel) 2021; 13:polym13040588. [PMID: 33669181 PMCID: PMC7919642 DOI: 10.3390/polym13040588] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2021] [Revised: 02/03/2021] [Accepted: 02/11/2021] [Indexed: 12/02/2022] Open
Abstract
The imaging of non-conducting materials by scanning electron microscopy (SEM) is most often performed after depositing few nanometers thick conductive layers on the samples. It is shown in this work, that even a 5 nm thick sputtered gold layer can dramatically alter the morphology and the surface structure of many different types of aerogels. Silica, polyimide, polyamide, calcium-alginate and cellulose aerogels were imaged in their pristine forms and after gold sputtering utilizing low voltage scanning electron microscopy (LVSEM) in order to reduce charging effects. The morphological features seen in the SEM images of the pristine samples are in excellent agreement with the structural parameters of the aerogels measured by nitrogen adsorption-desorption porosimetry. In contrast, the morphologies of the sputter coated samples are significantly distorted and feature nanostructured gold. These findings point out that extra care should be taken in order to ensure that gold sputtering does not cause morphological artifacts. Otherwise, the application of low voltage scanning electron microscopy even yields high resolution images of pristine non-conducting aerogels.
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Affiliation(s)
- Laura Juhász
- Department of Solid State Physics, University of Debrecen, Egyetem sqr. 1, H-4032 Debrecen, Hungary;
- Doctoral School of Physics, University of Debrecen, Egyetem sqr. 1, H-4032 Debrecen, Hungary
| | - Krisztián Moldován
- MTA-DE Redox and Homogeneous Catalytic Reaction Mechanisms Research Group, Department of Inorganic and Analytical Chemistry, University of Debrecen, Egyetem sqr. 1, H-4032 Debrecen, Hungary; (K.M.); (I.F.)
- Doctoral School of Chemistry, University of Debrecen, Egyetem sqr. 1, H-4032 Debrecen, Hungary
| | - Pavel Gurikov
- Laboratory for Development and Modelling of Novel Nanoporous Materials, Hamburg University of Technology, Eißendorfer Straße 38, 21073 Hamburg, Germany;
| | - Falk Liebner
- Institute for Chemistry of Renewable Resources, University of Natural Resources and Life Sciences, Vienna (BOKU), Konrad-Lorenz-Straße 24, A-3430 Tulln, Austria;
| | - István Fábián
- MTA-DE Redox and Homogeneous Catalytic Reaction Mechanisms Research Group, Department of Inorganic and Analytical Chemistry, University of Debrecen, Egyetem sqr. 1, H-4032 Debrecen, Hungary; (K.M.); (I.F.)
| | - József Kalmár
- MTA-DE Redox and Homogeneous Catalytic Reaction Mechanisms Research Group, Department of Inorganic and Analytical Chemistry, University of Debrecen, Egyetem sqr. 1, H-4032 Debrecen, Hungary; (K.M.); (I.F.)
- Correspondence: (J.K.); (C.C.); Tel.: +36-52-512-900 (J.K.); +36-52-316-073 (C.C.)
| | - Csaba Cserháti
- Department of Solid State Physics, University of Debrecen, Egyetem sqr. 1, H-4032 Debrecen, Hungary;
- Correspondence: (J.K.); (C.C.); Tel.: +36-52-512-900 (J.K.); +36-52-316-073 (C.C.)
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11
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Forgács A, Papp V, Paul G, Marchese L, Len A, Dudás Z, Fábián I, Gurikov P, Kalmár J. Mechanism of Hydration and Hydration Induced Structural Changes of Calcium Alginate Aerogel. ACS APPLIED MATERIALS & INTERFACES 2021; 13:2997-3010. [PMID: 33401895 DOI: 10.1021/acsami.0c17012] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The most relevant properties of polysaccharide aerogels in practical applications are determined by their microstructures. Hydration has a dominant role in altering the microstructures of these hydrophilic porous materials. To understand the hydration induced structural changes of monolithic Ca-alginate aerogel, produced by drying fully cross-linked gels with supercritical CO2, the aerogel was gradually hydrated and characterized at different states of hydration by small-angle neutron scattering (SANS), liquid-state nuclear magnetic resonance (NMR) spectroscopy, and magic angle spinning (MAS) NMR spectroscopy. First, the incorporation of structural water and the formation of an extensive hydration sphere mobilize the Ca-alginate macromolecules and induce the rearrangement of the dry-state tertiary and quaternary structures. The primary fibrils of the original aerogel backbone form hydrated fibers and fascicles, resulting in the significant increase of pore size, the smoothing of the nanostructured surface, and the increase of the fractal dimension of the matrix. Because of the formation of these new superstructures in the hydrated backbone, the stiffness and the compressive strength of the aerogel significantly increase compared to its dry-state properties. Further elevation of the water content of the aerogel results in a critical hydration state. The Ca-alginate fibers of the backbone disintegrate into well-hydrated chains, which eventually form a quasi-homogeneous hydrogel-like network. Consequently, the porous structure collapses and the well-defined solid backbone ceases to exist. Even in this hydrogel-like state, the macroscopic integrity of the Ca-alginate monolith is intact. The postulated mechanism accounts for the modification of the macroscopic properties of Ca-alginate aerogel in relation to both humid and aqueous environments.
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Affiliation(s)
- Attila Forgács
- Department of Inorganic and Analytical Chemistry, University of Debrecen, Egyetem tér 1, Debrecen H-4032, Hungary
- MTA-DE Redox and Homogeneous Catalytic Reaction Mechanisms Research Group, Egyetem tér 1, Debrecen H-4032, Hungary
| | - Vanda Papp
- Department of Inorganic and Analytical Chemistry, University of Debrecen, Egyetem tér 1, Debrecen H-4032, Hungary
| | - Geo Paul
- Department of Science and Technological Innovation, Universitá del Piemonte Orientale, Viale T. Michel 11, 15121 Alessandria, Italy
| | - Leonardo Marchese
- Department of Science and Technological Innovation, Universitá del Piemonte Orientale, Viale T. Michel 11, 15121 Alessandria, Italy
| | - Adél Len
- Neutron Spectroscopy Department, Centre for Energy Research, Konkoly-Thege Miklós út 29-33, Budapest H-1121, Hungary
| | - Zoltán Dudás
- Neutron Spectroscopy Department, Centre for Energy Research, Konkoly-Thege Miklós út 29-33, Budapest H-1121, Hungary
| | - István Fábián
- Department of Inorganic and Analytical Chemistry, University of Debrecen, Egyetem tér 1, Debrecen H-4032, Hungary
- MTA-DE Redox and Homogeneous Catalytic Reaction Mechanisms Research Group, Egyetem tér 1, Debrecen H-4032, Hungary
| | - Pavel Gurikov
- Laboratory for Development and Modelling of Novel Nanoporous Materials, Hamburg University of Technology, Eißendorfer Straße 38, 21073 Hamburg, Germany
| | - József Kalmár
- Department of Inorganic and Analytical Chemistry, University of Debrecen, Egyetem tér 1, Debrecen H-4032, Hungary
- MTA-DE Redox and Homogeneous Catalytic Reaction Mechanisms Research Group, Egyetem tér 1, Debrecen H-4032, Hungary
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12
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Faasen DP, Jarray A, Zandvliet HJW, Kooij ES, Kwiecinski W. Hansen solubility parameters obtained via molecular dynamics simulations as a route to predict siloxane surfactant adsorption. J Colloid Interface Sci 2020; 575:326-336. [PMID: 32387741 DOI: 10.1016/j.jcis.2020.04.070] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2020] [Revised: 04/17/2020] [Accepted: 04/17/2020] [Indexed: 11/25/2022]
Abstract
HYPOTHESIS The Hansen Solubility Parameters (HSP) derived from Molecular Dynamics (MD) simulations can be used as a fast approach to predict surfactants adsorption on a solid surface. Experiments and simulations: We focused on the specific case of siloxane-based surfactants adsorption on silicon oxide surface (SiO2), encountered in inkjet printing processes. A simplified atomistic model of the SiO2 surface was designed to enable the computation of its solubility parameter using MD, and to subsequently determine the interactions of the SiO2 surface with the siloxane-based surfactant and the various solvents employed. Surfactant adsorption was characterized experimentally using contact angle goniometry, ellipsometry, XPS and AFM. FINDINGS Comparison of the numerical results with experiments showed that the HSP theory allows to identify the range of solvents that are likely to prevent surfactant adsorption on the SiO2 surface. The proposed approach indicates that polar solvents, such as acetone and triacetin, which are strongly attracted to the silicon oxide surface might form a shield that prevents siloxane-based surfactants adsorption. This simple approach, can guide the selection of adequate solvents for surfaces and surfactants with specific chemical structures, providing opportunities for controlling interfacial adsorption.
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Affiliation(s)
- Daniël P Faasen
- Physics of Interfaces and Nanomaterials Group, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, the Netherlands.
| | - Ahmed Jarray
- Multi Scale Mechanics (MSM), MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, the Netherlands.
| | - Harold J W Zandvliet
- Physics of Interfaces and Nanomaterials Group, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, the Netherlands.
| | - E Stefan Kooij
- Physics of Interfaces and Nanomaterials Group, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, the Netherlands.
| | - Wojciech Kwiecinski
- Physics of Interfaces and Nanomaterials Group, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, the Netherlands.
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13
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Papastergiou M, Chriti D, Damalas DE, Raptopoulos G, Paraskevopoulou P. Poly(urethane-acrylate) aerogels from the isocyanurate trimer of isophorone diisocyanate. J Supercrit Fluids 2019. [DOI: 10.1016/j.supflu.2019.02.020] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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14
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Wu B, Zhu G, Dufresne A, Lin N. Fluorescent Aerogels Based on Chemical Crosslinking between Nanocellulose and Carbon Dots for Optical Sensor. ACS APPLIED MATERIALS & INTERFACES 2019; 11:16048-16058. [PMID: 30977364 DOI: 10.1021/acsami.9b02754] [Citation(s) in RCA: 51] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Generally produced by solvent sublimation via freeze-drying or critical point drying treatment, nanocellulose-based aerogels have attracted considerable interest in offering the features such as sustainability, available surface reactivity, lightweight, high porosity, and specific surface area. This study presents a novel strategy for the preparation of fluorescent aerogels based on covalent linkage between the natural skeleton of a cellulose nanofibril (CNF) and a fluorescent carbon dot (CD). The maximum CD grafting content on the CNF-based aerogel was 113 mg g-1, providing bright blue fluorescence under ultraviolet radiation with a high fluorescence quantum yield of 26.2%. Besides improved mechanical properties with a 360% increase in compression strength, the covalently bonded CD nanoparticle further serves as a structural stabilizer to endow the characteristic of shape recovery in water for the fabricated fluorescent aerogel. Finally, this aerogel displays high sensitivity and selection on the recognition of NO x and aldehyde species, which is studied for the detection of glutaraldehyde at ultralow concentrations (ppm) in water. Using the innovation of an organic solvent-free route and avoiding the toxic crosslinking reagents or fluorescent sources, the CNF/CD-based fluorescent aerogel developed in this study is a promising functional material for potential optical sensing application.
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Affiliation(s)
- Bolang Wu
- School of Chemistry, Chemical Engineering and Life Sciences , Wuhan University of Technology , Wuhan 430070 , P. R. China
| | - Ge Zhu
- Université Grenoble Alpes, Grenoble INP*, LGP2 , F-38000 Grenoble , France (* Institute of Engineering Université Grenoble Alpes, Grenoble, France)
| | - Alain Dufresne
- Université Grenoble Alpes, Grenoble INP*, LGP2 , F-38000 Grenoble , France (* Institute of Engineering Université Grenoble Alpes, Grenoble, France)
| | - Ning Lin
- School of Chemistry, Chemical Engineering and Life Sciences , Wuhan University of Technology , Wuhan 430070 , P. R. China
- Anhui Province Key Laboratory of Environment-friendly Polymer Materials , Anhui University , Hefei 230601 , P. R. China
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15
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Takeshita S, Sadeghpour A, Malfait WJ, Konishi A, Otake K, Yoda S. Formation of Nanofibrous Structure in Biopolymer Aerogel during Supercritical CO 2 Processing: The Case of Chitosan Aerogel. Biomacromolecules 2019; 20:2051-2057. [PMID: 30908038 DOI: 10.1021/acs.biomac.9b00246] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Supercritical drying is widely considered as the gold standard to produce aerogels that preserve the microstructure of the gels, but we have found this is not always the case. Chitosan aerogel, one of the emerging biopolymer aerogels, was prepared by chemical cross-linking gelation, followed by solvent exchange with methanol and supercritical drying using CO2. Small-angle X-ray scattering analysis shows that the structure of the wet gel, which consists of Gaussian chains of individual molecular strands, converts into a nanofibrous network during CO2 processing. In situ observation reveals a drastic shrinkage of the gel in CO2, demonstrating that physical coagulation caused by the low affinity between chitosan and CO2 is the main structure-forming step. These results challenge the common perception of supercritical drying: it is no longer an inactive drying method, but rather an active nanostructure forming a tool to produce porous biopolymer materials with tailored structure and properties.
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Affiliation(s)
- Satoru Takeshita
- Research Institute for Chemical Process Technology , National Institute of Advanced Industrial Science and Technology (AIST) , Tsukuba 3058565 , Japan
| | - Amin Sadeghpour
- Center for X-ray Analytics , Empa, Swiss Federal Laboratories for Materials Science and Technology , St. Gallen CH-9014 , Switzerland
| | - Wim J Malfait
- Laboratory for Building Energy Materials and Components , Empa, Swiss Federal Laboratories for Materials Science and Technology , Dübendorf CH-8600 , Switzerland
| | - Arata Konishi
- Department of Industrial Chemistry , Tokyo University of Science , Tokyo 1628601 , Japan
| | - Katsuto Otake
- Department of Industrial Chemistry , Tokyo University of Science , Tokyo 1628601 , Japan
| | - Satoshi Yoda
- Research Institute for Chemical Process Technology , National Institute of Advanced Industrial Science and Technology (AIST) , Tsukuba 3058565 , Japan
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16
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Taghvaee T, Donthula S, Rewatkar PM, Majedi Far H, Sotiriou-Leventis C, Leventis N. K-Index: A Descriptor, Predictor, and Correlator of Complex Nanomorphology to Other Material Properties. ACS NANO 2019; 13:3677-3690. [PMID: 30839204 DOI: 10.1021/acsnano.9b00396] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Morphology is a qualitative property of nanostructured matter and is articulated by visual inspection of micrographs. For deterministic procedures that relate nanomorphology to synthetic conditions, it is necessary to express nano- and microstructures numerically. Selecting polyurea aerogels as a model system with demonstrated potential for rich nanomorphology and guided by a statistical design-of-experiments model, we prepared a large array of materials (208) with identical chemical composition but quite different nanostructures. By reflecting on SEM imaging, it was realized that our first preverbal impression about a nanostructure is related to its openness and texture; the former is quantified by porosity ( Π), and the latter is oftentimes related to hydrophobicity, which, in turn, is quantified by the contact angle (θ) of water droplets resting on the material. Herewith, the θ-to-Π ratio is referred to as the K-index, and it was noticed that all polyurea samples of this study could be put in eight K-index groups with separate nanomorphologies ranging from caterpillar-like assemblies of nanoparticles, to thin nanofibers, to cocoon-like structures, to large bald microspheres. A first validation of the K-index as a morphology descriptor was based on compressing samples to different strains: it was observed that as the porosity decreases, the water-contact angle decreases proportionally, and thereby the K-index remains constant. The predictive power of the K-index was demonstrated with 20 polyurea aerogels prepared in 8 binary solvent systems. Subsequently, several material properties were correlated to nanomorphology through the K-index and that, in turn, provided insight about the root cause of the diversity of the nanostructure in polyurea aerogels. Finally, using response surface methodology, K-indexes and other material properties of practical interest were correlated to the monomer, water, and catalyst concentrations as well as the three Hansen solubility parameters of the sol. That enabled the synthesis of materials with up to six prescribed properties at a time, including nanomorphology, bulk density, BET surface area, elastic modulus, ultimate compressive strength, and thermal conductivity.
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Affiliation(s)
- Tahereh Taghvaee
- Department of Chemistry , Missouri University of Science and Technology , Rolla , Missouri 65409 , United States
| | - Suraj Donthula
- Department of Chemistry , Missouri University of Science and Technology , Rolla , Missouri 65409 , United States
| | - Parwani M Rewatkar
- Department of Chemistry , Missouri University of Science and Technology , Rolla , Missouri 65409 , United States
| | - Hojat Majedi Far
- Department of Chemistry , Missouri University of Science and Technology , Rolla , Missouri 65409 , United States
| | - Chariklia Sotiriou-Leventis
- Department of Chemistry , Missouri University of Science and Technology , Rolla , Missouri 65409 , United States
| | - Nicholas Leventis
- Department of Chemistry , Missouri University of Science and Technology , Rolla , Missouri 65409 , United States
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17
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Strong, compressible, bendable and stretchable silicone sponges by solvent-controlled hydrolysis and polycondensation of silanes. J Colloid Interface Sci 2019; 540:554-562. [DOI: 10.1016/j.jcis.2019.01.059] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2018] [Revised: 01/11/2019] [Accepted: 01/12/2019] [Indexed: 01/14/2023]
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18
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Jankovic S, Tsakiridou G, Ditzinger F, Koehl NJ, Price DJ, Ilie AR, Kalantzi L, Kimpe K, Holm R, Nair A, Griffin B, Saal C, Kuentz M. Application of the solubility parameter concept to assist with oral delivery of poorly water-soluble drugs – a PEARRL review. J Pharm Pharmacol 2018; 71:441-463. [DOI: 10.1111/jphp.12948] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2018] [Accepted: 05/28/2018] [Indexed: 01/29/2023]
Abstract
Abstract
Objectives
Solubility parameters have been used for decades in various scientific fields including pharmaceutics. It is, however, still a field of active research both on a conceptual and experimental level. This work addresses the need to review solubility parameter applications in pharmaceutics of poorly water-soluble drugs.
Key findings
An overview of the different experimental and calculation methods to determine solubility parameters is provided, which covers from classical to modern approaches. In the pharmaceutical field, solubility parameters are primarily used to guide organic solvent selection, cocrystals and salt screening, lipid-based delivery, solid dispersions and nano- or microparticulate drug delivery systems. Solubility parameters have been applied for a quantitative assessment of mixtures, or they are simply used to rank excipients for a given drug.
Summary
In particular, partial solubility parameters hold great promise for aiding the development of poorly soluble drug delivery systems. This is particularly true in early-stage development, where compound availability and resources are limited. The experimental determination of solubility parameters has its merits despite being rather labour-intensive because further data can be used to continuously improve in silico predictions. Such improvements will ensure that solubility parameters will also in future guide scientists in finding suitable drug formulations.
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Affiliation(s)
- Sandra Jankovic
- Department of Pharmaceutical Sciences, University of Basel, Basel, Switzerland
- Institute of Pharma Technology, University of Applied Sciences and Arts Northwestern Switzerland, Muttenz, Switzerland
| | - Georgia Tsakiridou
- Pharmathen SA, Product Design & Evaluation, Athens, Greece
- Faculty of Pharmacy, National and Kapodistrian University of Athens, Athens, Greece
| | - Felix Ditzinger
- Department of Pharmaceutical Sciences, University of Basel, Basel, Switzerland
- Institute of Pharma Technology, University of Applied Sciences and Arts Northwestern Switzerland, Muttenz, Switzerland
| | - Niklas J Koehl
- School of Pharmacy, University College Cork, Cork, Ireland
| | - Daniel J Price
- Merck Group, Molecule Characterisation, Darmstadt, Germany
- Goethe University, Frankfurt, Germany
| | - Alexandra-Roxana Ilie
- School of Pharmacy, University College Cork, Cork, Ireland
- Drug Product Development, Janssen Research and Development, Johnson & Johnson, Beerse, Belgium
| | - Lida Kalantzi
- Pharmathen SA, Product Design & Evaluation, Athens, Greece
| | - Kristof Kimpe
- Pharmaceutical Sciences, Janssen Research and Development, Johnson & Johnson, Beerse, Belgium
| | - René Holm
- Drug Product Development, Janssen Research and Development, Johnson & Johnson, Beerse, Belgium
| | - Anita Nair
- Merck Group, Molecule Characterisation, Darmstadt, Germany
| | | | - Christoph Saal
- Merck Group, Molecule Characterisation, Darmstadt, Germany
| | - Martin Kuentz
- Institute of Pharma Technology, University of Applied Sciences and Arts Northwestern Switzerland, Muttenz, Switzerland
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19
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Zhao S, Malfait WJ, Guerrero-Alburquerque N, Koebel MM, Nyström G. Biopolymer-Aerogele und -Schäume: Chemie, Eigenschaften und Anwendungen. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201709014] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Shanyu Zhao
- Building Energy Materials & Components; Eidgenössische Materialprüfungs- und Forschungsanstalt (Empa); Überlandstrasse 129 CH-8600 Dübendorf Schweiz
| | - Wim J. Malfait
- Building Energy Materials & Components; Eidgenössische Materialprüfungs- und Forschungsanstalt (Empa); Überlandstrasse 129 CH-8600 Dübendorf Schweiz
| | - Natalia Guerrero-Alburquerque
- Building Energy Materials & Components; Eidgenössische Materialprüfungs- und Forschungsanstalt (Empa); Überlandstrasse 129 CH-8600 Dübendorf Schweiz
| | - Matthias M. Koebel
- Building Energy Materials & Components; Eidgenössische Materialprüfungs- und Forschungsanstalt (Empa); Überlandstrasse 129 CH-8600 Dübendorf Schweiz
| | - Gustav Nyström
- Angewandte Holzforschung; Eidgenössische Materialprüfungs- und Forschungsanstalt (Empa); Überlandstrasse 129 CH-8600 Dübendorf Schweiz
- Departement Gesundheitswissenschaften und Technologie; ETH Zürich; Schmelzbergstrasse 9 CH-8092 Zürich Schweiz
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20
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Zhao S, Malfait WJ, Guerrero-Alburquerque N, Koebel MM, Nyström G. Biopolymer Aerogels and Foams: Chemistry, Properties, and Applications. Angew Chem Int Ed Engl 2018; 57:7580-7608. [DOI: 10.1002/anie.201709014] [Citation(s) in RCA: 336] [Impact Index Per Article: 56.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Indexed: 12/21/2022]
Affiliation(s)
- Shanyu Zhao
- Building Energy Materials & Components Laboratory; Swiss Federal Laboratories for Materials Science and Technology (Empa); Überlandstrasse 129 CH-8600 Dübendorf Switzerland
| | - Wim J. Malfait
- Building Energy Materials & Components Laboratory; Swiss Federal Laboratories for Materials Science and Technology (Empa); Überlandstrasse 129 CH-8600 Dübendorf Switzerland
| | - Natalia Guerrero-Alburquerque
- Building Energy Materials & Components Laboratory; Swiss Federal Laboratories for Materials Science and Technology (Empa); Überlandstrasse 129 CH-8600 Dübendorf Switzerland
| | - Matthias M. Koebel
- Building Energy Materials & Components Laboratory; Swiss Federal Laboratories for Materials Science and Technology (Empa); Überlandstrasse 129 CH-8600 Dübendorf Switzerland
| | - Gustav Nyström
- Applied Wood Materials Laboratory; Swiss Federal Laboratories for Materials Science and Technology (Empa); Überlandstrasse 129 CH-8600 Dübendorf Switzerland
- Department of Health Science and Technology; ETH Zurich; Schmelzbergstrasse 9 CH-8092 Zürich Switzerland
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