Correlation between the elastic modulus and heat transport along the solid phase in highly porous materials: Theoretical approaches and experimental validation using polyurea aerogels

Weigold, Lena; Reichenauer, Gudrun

doi:10.1016/j.supflu.2015.06.008

Cited by 6 publications

(4 citation statements)

References 28 publications

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“…The key parameters that allowed for a microstructural decoupling of mechanical and thermal properties were identified as the microscopic homogeneity of the solid network and the curvature of its network elements. In the second approach [ 70 ], similar studies were conducted with two series of samples prepared in the density range of 0.03 to 0.3 g·cm −3 . Again, the elastic modulus was found to correlate with solid thermal conductivity, irrespective of microstructural details.…”

Section: The Literature On Polyurea Aerogelsmentioning

confidence: 99%

Polyurea Aerogels: Synthesis, Material Properties, and Applications

Leventis

2022

Polymers

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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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Section: The Literature On Polyurea Aerogelsmentioning

confidence: 99%

Polyurea Aerogels: Synthesis, Material Properties, and Applications

Leventis

2022

Polymers

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“…While mechanical properties of monolithic materials with macroscopic dimensions are reliably determined by mechanical testing, respective data for hierarchical porous materials, exhibiting, for example, meso- and macroporosity, on their different structural levels are not easily accessible. Nevertheless, they are important to optimize the macroscopic moduli for handling and application as well as quantities related to them, such as thermal insulation properties. , Especially monolithic meso-macroporous materials used as a column in HPLC or flow catalysis require sufficient mechanical stability. , …”

Section: Introductionmentioning

confidence: 99%

“…Nevertheless, they are important to optimize the macroscopic moduli for handling and application as well as quantities related to them, such as thermal insulation properties. 1,2 Especially monolithic meso-macroporous materials used as a column in HPLC or flow catalysis require sufficient mechanical stability. 3,4 Different approaches are available to access mechanical properties such as…”

Section: Introductionmentioning

confidence: 99%

Determining Mechanical Moduli of Disordered Materials with Hierarchical Porosity on Different Structural Levels

et al. 2022

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The impact of synthesis parameters and structural properties, respectively, on mechanical properties of porous materials on different structural levels provides valuable information for designing materials for specific applications. Within this study, we apply two nonstandard approaches for determining the mechanical properties of the mesoporous backbone phase in a series of disordered SiO2-based monolithic materials possessing hierarchical meso-macroporosity, that is, deformation upon mercury porosimetry and in situ dilatometry during nitrogen adsorption analysis. By using ordered porous model materials, the latter method has been recently proven to provide reliable mechanical moduli. This concept was now applied to a SiO2 monolith developed for high-performance liquid chromatography exhibiting disordered hierarchical meso- and macroporosity, as well as a series of analogue phenyl-modified meso-macroporous SiO2 monoliths with up to 36.1 at% organic modification. The phenyl group was introduced by adding phenyltrimethoxysilane to the sol–gel mixture. The study aimed at investigating in detail the impact of the organic modification on the morphology of the porous solid and the resulting mechanical properties. The study shows that both Hg porosimetry and in situ dilatometry performed during N2 adsorption at 77 K provide similar and reasonable moduli of compression for the mesoporous backbone of the silica materials investigated. These data were compared with moduli of the macroscopic sample as determined from sound velocity measurements by describing the fully connected macroporous backbone with a foam model. The comparison reveals an otherwise overseen side effect of the organic modification of the silica framework: in contrast to the pure reference SiO2 meso-macroporous monoliths, the hybrid material is composed of a more particulate morphology on the mesoscale, that is, mesoporous particles and corresponding necks between them are formed, which results in significant softening of the porous solid on the macroscale.

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“…Although the mechanical properties and solid-phase thermal conductivities (representing the main thermal transport path in ambient conditions) of aerogels are connected to the porosity in a first-order approximation [4][5][6], these properties are also strongly controlled by other characteristics, such as the branching of the gel backbone and its connectivity, as Processes 2021, 9, 672 2 of 12 well as the necks between the subunits forming the gel skeleton, i.e., properties that are hard to quantify experimentally. Within the material development process, analysis by small-angle X-ray scattering (SAXS) provides fast characterization of structural quantities such as specific surface area and branching (fractality) of the solid phase, as well as particle and cluster size.…”

Section: Introductionmentioning

confidence: 99%

Advances in the Development of Sol-Gel Materials Combining Small-Angle X-ray Scattering (SAXS) and Machine Learning (ML)

et al. 2021

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The requirements for new materials are increasing with each new application, which, in most cases, means an enhancement in the complexity of the development process. Nanoporous sol-gel-based materials, especially aerogels, are promising candidates for thermal superinsulation, electrodes for energy conversion and storage or high-end adsorbers. Their synthesis and processing route is complex, and the relationship between the material/processing parameters and the resulting structural and physical properties is not straightforward. Using small-angle X-ray scattering (SAXS) allows for fast structural characterization of both the gel and the resulting aerogel; combining these results with the respective physical properties of the aerogels and using these data as inputs for machine learning (ML) algorithms provide an approach to predict physical properties on the basis of a structural dataset. This data-driven strategy may be a feasible approach to speed up the development process. Thus, the study aimed to provide a proof of concept of ML-based model derivation from material, process and SAXS data to predict physical properties such as the solid-phase thermal conductivity (λs) of silica aerogels from a structural dataset. Here, we used different data subsets as predictors according to different states of synthesis (wet and dry) to evaluate the model performance.

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Correlation between the elastic modulus and heat transport along the solid phase in highly porous materials: Theoretical approaches and experimental validation using polyurea aerogels

Cited by 6 publications

References 28 publications

Polyurea Aerogels: Synthesis, Material Properties, and Applications

Polyurea Aerogels: Synthesis, Material Properties, and Applications

Determining Mechanical Moduli of Disordered Materials with Hierarchical Porosity on Different Structural Levels

Advances in the Development of Sol-Gel Materials Combining Small-Angle X-ray Scattering (SAXS) and Machine Learning (ML)

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