Properties Of Aerogels Research Articles

Preparation of SiO2 aerogel by water glass: effect of different sodium removal methods on aerogel properties

Preparation of SiO2 aerogel by water glass: effect of different sodium removal methods on aerogel properties

Preparation and physical properties of basalt fiber-reinforced silica aerogels

Preparation and physical properties of basalt fiber-reinforced silica aerogels

Upcycling stale bread into (meso)porous materials: xerogels and aerogels

This work explores the upcycling of stale bread into bio-based, low-density porous materials with partial mesoporosity, produced through gelatinization and drying, using either supercritical CO2 (aerogels) or low-vacuum conditions (xerogels). Cryogels were also fabricated via freeze-drying for comparison purposes. Stale bread particles (Bread) were subjected to proteolytic gluten depletion (Gluten-Depleted Bread, GDB) or particle size reduction (Finely milled Bread, FB) to investigate the effect of protein removal or particle size on porous materials’ properties. Porous materials made from wheat starch (WS) and wheat flour (Flour) were also examined for comparison. The solvent exchange induced volume shrinkage (SE-VS), which accounted for over 87% of the total shrinkage, ranged from 62% in GDB to 78% in WS. Bread-based porous materials presented comparable specific surface area (∼ 40 m2/g) and water absorption capacity (∼ 400%) to WS materials, but outperformed in resistance to volume shrinkage, resulting in lower density. FB porous materials possessed a higher specific surface area than Bread materials, indicating the benefits of particle size reduction. Furthermore, gluten depletion resulted in GDB-aerogels with the highest specific surface area (∼ 80 m2/g), highlighting the benefits of gluten depletion. However, WS materials exhibited significantly greater maximum compressive stress (> 2.0 MPa) and compressive modulus (> 6 MPa) than stale bread-based porous materials. Importantly, the porous properties of xerogels and aerogels were similar (differences < 10%), indicating the feasibility of using low vacuum drying to produce new porous materials with partial mesoporosity (surface area 60–80 m2/g) from stale bread at a lower cost.

Ease-of-manufacture highly transparent thin polyvinyl alcohol aerogel

The earliest silicon-based aerogels attracted attention due to their nanoscale porous structure and high transparency. Still, they need to be more balanced with the poor mechanical properties. Their brittle structure limits the development of this promising new material. Therefore, the goal of this work is to optimize the mechanical properties of aerogels while maintaining transparency. The good mechanical properties of polymers have made them the material of choice for this work. Polyvinyl alcohol (PVA), which can undergo self-crosslinking through side-chain hydroxyl groups forming hydrogen bonds, was chosen as the raw material to simplify and expedite the production process. The production process was experimented with, analyzed, and refined. Considering the time efficiency of the experimental process, a one-step gelling method was invented to facilitate the sol-gel transition. The one-step gelling method maintained the high transparency of PVA aerogels and reduced the time required for the gelation process compared to the freeze-thawing method. This work employs carbon dioxide supercritical drying to ensure minimal structural collapse and maximize the porous structure’s retention. The transmittance of PVA aerogels can reach up to 93.67% at a wavelength of 1333 nm. The internal structure of aerogels with different PVA concentrations was observed using a Scanning electron microscope. Applying Beer-Lambert’s Law eliminated the effect of sample thickness on transparency. The relationship between the transparency of PVA aerogels, their microstructure, and macroscopic concentration was studied and analyzed for the first time. While ensuring light transmittance, the modulus of the PVA aerogel reached as high as 6.18 ± 0.56 MPa at 13 wt%.

Regulation of Adsorption Properties of Whey Protein Isolate Fibril-Calcium Alginate Aerogels by Controlling Protein Fibrillation Time.

Amyloid-like fibrils have a relatively high specific surface area, which makes them suitable as absorbents. In this study, we prepared absorbent composite aerogels from whey protein isolate fibril (WPIF) and calcium alginate (CA). The impact of protein fibrillation time (4-24 h) on the adsorption properties of these aerogels was assessed, as this influences the nature of the WPIFs formed. Fourier transform infrared spectroscopy analysis indicated that hydrogen bonding, hydrophobic interactions, and electrostatic interactions were the main molecular interactions in the composite aerogels. Then, the adsorption properties of the aerogels were investigated using crystal violet as a model compound. The adsorption properties of all composite aerogels were significantly improved compared to CA aerogels, which was mainly attributed to the numerous functional groups of the surfaces of the WPIFs, as well as the rougher surface topology of the composite aerogels. The adsorption capacity of the composite aerogels first increased and then decreased with increasing fibrillation time, with 8 h fibrillation leading to the largest adsorption capacity (1886.11 mg/g). Thioflavin T fluorescence, atomic force microscopy, light extinction, average particle size, and zeta potential analysis indicated that the high fibril content, mature fibril morphology, large number of available functional groups on the surface, and relatively low zeta potential of WPIF8 might be the main reasons. Adsorption kinetics and isothermal adsorption profile analysis suggested that monolayer adsorption occurred through chemical adsorption processes. The edible aerogel with high adsorption properties developed in this work has potential application in food and biomedical fields.

Effect of Solvents on the Performance and Structure of Polymethylacrylimide Aerogels.

Solvent effects play a critical role in solution polymerization, especially in free radical polymerization, where they influence both monomer-solvent interactions and the resulting polymer structure. In this study, polymethacrylimide (PMI) aerogels were synthesized via freeze-drying using dimethylformamide (DMF), dimethylacetamide (DMAc), and dimethyl sulfoxide (DMSO) as solvents. The effects of monomer reactivity ratios, monomer distribution, and solvent-monomer interactions on the shrinkage, bulk density, pore size, and compressive properties of the aerogels were investigated. Results demonstrated that solvent choice significantly impacted the polymerization process, leading to variations in the structure and properties of the final aerogels. Notably, aerogels synthesized in DMSO, the most polar solvent, exhibited the lowest shrinkage (33.98%), highest density (0.1582 g·cm-3), and highest compressive stress (1695.48 kPa at 70% strain). These findings underscore the importance of solvent selection in controlling the microstructure and enhancing the mechanical performance of PMI aerogels.

Ceramic Microsphere Aerogels by Curled Precursor Molecular Chain: Antishrinkage, Thermal Insulation and Multiscale Simulations.

Ceramic aerogels prepared by the route of polymer-derived ceramics (PDCs) have been of significant attention in high-temperature insulation. However, the application of ceramic aerogels was seriously confined due to the structural damage and shrinkage cracking of ceramic precursors during pyrolysis. In this investigation, precursor ceramic microsphere aerogels with outstanding antishrinkage properties were prepared by storing strain in curled molecular chains and using polysilazane (PSZ) as the precursor. Meanwhile, precursor ceramic microsphere aerogels with different curled molecular chain structures were prepared by modulating solvent interactions and cross-linked structures. Different curled molecular chain structures were formed, and the impact on the antishrinkage properties of precursor aerogels was analyzed. The shrinkage resistance, thermal insulation, and mechanical properties of the prepared aerogels were tested and compared. Furthermore, the mechanism of the impact of different curled molecular chain structures on thermal insulation and mechanical properties was investigated through multiscale simulations combined with fractal theory. The thermal and stress transfer at the interfaces of different microsphere skeleton structures and the mechanisms were investigated. An idea for solving the problem of pyrolytic shrinkage in the preparation of ceramic aerogels was provided in this investigation. In addition, insights into the influence of the microsphere skeleton structure on the thermal and mechanical properties of ceramic aerogels were provided.

Preparation and Properties of Flexible Phenolic Silicone Hybrid Aerogels for Thermal Insulation

In order to prepare flexible thermal protection aerogel materials, using dimethyldimethoxysilane (DMDMS) and methyltrimethoxysilane (MTMS) as co-precursors, isocyanate-propyltrimethoxysilane (CFS-006) was added to the co-precursor as a coupling agent, and resorcinol and formaldehyde were added to the sol solution to prepare a phenolic silicone hybrid aerogel (FAS) by the sol–gel method. The prepared FAS aerogel had no phase separation problem, the density was only 0.118 g/cm3, the hydrophobic angle reached 155.3°, and it had certain flexibility. It could be compressed to 70% and still be restored to its original state. The FAS aerogel also had a low thermal conductivity of 0.0318 W/(m·K) and good high temperature insulation. The introduction of phenolic groups improved thermal stability; Tmax increased to 643.7 °C, and the residual carbon rate was 24.5%. This work has positive significance for the future combination of aerogels and textiles in the preparation of firefighting protective clothing.

Prediction of Broadband and Highly-Efficient Electromagnetic Wave-Absorbing SiC@SiO2 Nanowire Aerogel by Genetic Algorithm.

Searching for lightweight and high-temperature stable electromagnetic wave-absorbing materials with broad absorbing bandwidth and high efficiency is of significance for applications in daily life and industry. Optimizing the dielectric properties of SiC nanowire aerogel by both compositional and structural designs is an efficient way to obtain simultaneous efficient wave-dissipation ability and good impendence matching and thus the desired properties. However, due to the complex effects of dielectric parameters on the wave-absorbing properties, rational design of high-performance electromagnetic wave-absorbing materials remains challenging. Herein, we propose a genetic algorithm-based approach to predict broadband and highly efficient electromagnetic wave-absorbing materials in a SiC@SiO2 nanowire aerogel-based system. The obtained SiC@SiO2 nanowire aerogels exhibit a gradient multilayered structure with a low dielectric outer layer, a medium layer with alternatively distributed electromagnetic wave transparent and attenuation layers, and an inner high attenuation layer, giving it a broadband electromagnetic wave-absorbing performance covering almost all the 2-18 GHz bandwidth and simultaneous high efficiency. The results show that the genetic algorithm-based approach is efficient in predicting high-performance electromagnetic wave-absorbing ceramic aerogels.

Recent Advances in MXene-Based Aerogels for Electromagnetic Wave Absorption.

Developing lightweight, high-performance electromagnetic wave (EMW) absorbing materials those can absorb the adverse electromagnetic radiation or waves are of great significance. Transition metal carbides and/or nitrides (MXenes) are a novel type of 2D nanosheets associated with a large aspect ratio, abundant polar functional groups, adjustable conductivity, and remarkable mechanical properties. This contributes to the high-efficiency assembly of MXene-based aerogels possessing the ultra-low density, large specific surface area, tunable conductivity, and unique 3D porous microstructure, which is beneficial for promoting the EMW absorption. Therefore, MXene-based aerogels for EMW absorption have attracted widespread attention. This review provides an overview of the research progress on MXene-based aerogels for EMW absorption, focusing on the recent advances in component and structure design strategies, and summarizes the main strategies for constructing EMW absorbing MXene-based aerogels. In addition, based on EMW absorption mechanisms and structure regulation strategies, the preparation methods and properties of MXene-based aerogels with varieties of components and pore structures are detailed to advance understanding the relationships of composition-structure-performance. Furthermore, the future development and challenges faced by MXene-based aerogels for EMW absorption are summarized and prospected.

Cellulose nanofiber aerogels: effect of the composition and the drying method

Highly porous and lightweight aerogels of cellulose nanofibers (CNFs) have emerged as a promising class of material. This study delves into the impact of the composition (lignocellulose nanofibers–LCNFs and CNFs) and the drying methods (supercritical drying and freeze-drying) on the morphology and the properties of nanocellulose-based aerogels. The investigation evaluates the concentrations of nanofibers and the influence of lignin, a constituent of LCNFs recognized for enhancing the rigidity of plant cell walls, on the aerogel’s properties. The shrinkage rates, density, pore structure, and mechanical properties of the obtained aerogels are comprehensively compared. Supercritical drying proves advantageous for aerogel formation, resulting in materials with lower density and higher surface area than their freeze-dried counterparts at each concentration level. The use of acetone for supercritical drying contributes to reduce the shrinkage rates compared to ethanol. This decrease is attributed to the formation of a more rigid hydrogel during solvent exchange. Freeze-drying exhibits the lowest shrinkage rates and relatively higher porosity. The presence of lignin in the nanofibers influences the microstructure, yielding smoother and thicker pore walls. This study contributes to the comprehensive understanding of the intricate factors shaping nanocellulose aerogel properties, paving the way for the development of innovative and environmentally-friendly materials.

Molecular dynamics method to investigate the interaction energy and mechanical properties of the reinforced graphene aerogel with paraffin as the phase change material in the presence of different external heat fluxes

BackgroundGraphene aerogels (GA), known for their exceptional lightweight and sturdy characteristics, present a promising avenue for improving thermal energy (TE) storage and transfer efficiency. It might be possible to make better thermal management systems in fields like electronics, aerospace, and energy storage by studying how heat flux (HF) affects the strength and stability of graphene aerogels. MethodsThe study used molecular dynamics (MD) simulation to investigate how the mechanical properties of graphene aerogels strengthened with paraffin as phase change material (PCM) change in response to external heat flux (EHF). These simulation methods provided a detailed view of molecular interactions and dynamics at the atomic level, allowing researchers to understand the behavior of materials under various conditions. The change in toughness, interaction energy (IE), Young's modules (YM), and ultimate strength (US) was examined for this reason. Significant findingsThe results indicate that when the HF increased from 0.1 to 0.3 W/m2, the ultimate strength and Young's modules increased from 8.91 and 5.37 GPa to 14.546 and 8.59 GPa, respectively. These values declined when HF increased by more than 0.3 W/m2. When EHF went up to 0.3 W/m², these graphene aerogel properties went up. This was because the atoms moved around more and there were more bonding contacts among the graphene sheets, which made the structure of material stronger. However, at heat flux levels exceeding 0.3 W/m², excessive thermal energy may lead to thermal degradation, causing bond breakage and loss of structural integrity, ultimately resulting in a decrease in these mechanical properties. Also, the results reveal that interaction energy increased from -1522.098 to -1546.325 eV as external HF increased to 0.3 W/m2. The thermal motion of atoms enhanced as the HF increased, enabling closer clustering and better alignment of graphene sheets, thereby strengthening their interactions. This study gave us useful information about how to improve the mechanical properties of graphene aerogels in different HF conditions. This made it more likely that these materials can be used in energy storage systems and thermal management.

Enhanced post-combustion CO2 capture and direct air capture by plasma surface functionalization of graphene adsorbent

Graphene has enormous potential to capture CO2 due to its unique properties and cost-effectiveness. However, graphene-based adsorbents have drawbacks of lower CO2 adsorption capacity and poor selectivity. This work demonstrates a one-step rapid and sustainable N2/H2 plasma treatment process to prepare graphene-based sorbent material with enhanced CO2 adsorption performance. Plasma treatment directly enriches amine species, increases surface area, and improves textural properties. The CO2 adsorption capacity increases from 1.6 to 3.3 mmol/g for capturing flue gas, and from 0.14 to 1.3 mmol/g for direct air capture (DAC). Importantly, the electrothermal property of the plasma-modified aerogels has been significantly improved, resulting in faster heating rates and significantly reducing energy consumption compared to conventional external heating for regeneration of sorbents. Modified aerogels display improved selectivity of 42 and 87 after plasma modification for 5 and 10 min, respectively. The plasma-treated aerogels display minimal loss between 17% and 19% in capacity after 40 adsorption/desorption cycles, rendering excellent stability. The N2/H2 plasma treatment of adsorbent materials would lower energy expenses and prevent negative effects on the global economy caused by climate change.

Effect of supercritical CO2 drying variables and gel composition on the textural properties of cellulose aerogels

Cellulose aerogels are interesting platforms for biomedical and drug delivery applications, due to their biocompatibility, biodegradability, water absorption capacity, and good textural properties. Supercritical CO2 drying has been proven as an efficient technology for obtaining aerogels and preserving the porous structure. In this work, the effect of relevant process variables (CO2 density, depressurization rate, and intermediate depressurization mode) and gel composition on the textural properties of cellulose aerogels is studied. Experiments are performed in batch-mode, and aerogel monoliths are characterized in terms of apparent density, porosity, specific surface area, and crystalline morphology. Water uptake in different buffer solutions is also evaluated. The use of thiourea in the gel formation leads to lower porosity. On the other hand, higher porosity and surface area are obtained when depressurization is slow and the system is only partially depressurized between drying cycles. Aerogels showed a good and fast water uptake capacity, regardless of the pH (200–500 %).

Ambient drying to fabricate polybenzoxazine aerogels for thermal insulation in aerospace

Polybenzoxazine (PBz) aerogels are promising high-performance, halogen-free flame-retardant thermal insulation materials in aerospace applications. But their widespread use is hindered by high costs, significant drying shrinkage, and poor machinability. Herein, we successfully addressed these challenges by developing PBz aerogel composites using a cost-effective ambient pressure drying method that reduces energy consumption and shortening the preparation cycle. This approach expands the range of available monomers, reduces the inherent rigidity of the network structure, and enhances processability. The resulting PBz aerogels demonstrate low drying shrinkage (as low as 5.68 %), lightweight properties (lowest to 0.322 g cm−3), excellent fire-retardant (self-extinguishing in 1.8 s), and exceptional thermal insulation performance (as low as 0.0402 W m−1 K−1 at room temperature and normal pressure). Further studies under various pressures show that at an atmospheric pressure of 10 Pa, the thermal conductivity at room temperature can reach as low as 0.027 W m−1 K−1. Moreover, cryogenic treatment at −196 °C significantly enhances the compressive properties of PBz aerogels without inducing any noticeable shrinkage. Notably, PBz aerogels exhibit outstanding flame resistance, rated as nonflammable rating in vertical burning tests (UL-94, V-1 class), and showing a limiting oxygen index (LOI) as high as 33.7 %. Overall, these remarkable features underscore the exceptional potential of PBz aerogels as advanced thermal insulation materials in the aerospace industry.

Advancing sustainable molded packaging: Integrating silica aerogel into recycled paper pulp for the fabrication of thermally and mechanically stable superhydrophobic composites

In recent years, the growing demand for sustainable packaging has significantly fueled the quest to explore novel approaches that enhance the applicability of renewable alternatives. This study leverages the unique properties of silica aerogel (SA) to address the limitations of traditional molded pulp products. By integrating SA into recycled paper pulp (RP), we aimed to improve water resistance, thermal stability, and mechanical properties. Composites were prepared with varying SA concentrations (1–10 %). Contact angle measurements showed enhanced hydrophobicity, with RP/SA3 % achieving a contact angle of 152.09°, compared to 122.39° for neat RP. The tensile index (TI) of RP/SA composites with 3 % SA increased by 21.09 % compared to neat RP, indicating better mechanical strength. Thermal conductivity significantly decreased, with RP/SA10 % reducing from 0.155 W m−1·K−1 in neat RP to 0.088 W m−1·K−1, a 43.2 % improvement in thermal insulation. Additionally, composites with 1 % and 3 % SA maintained high biodegradability, showing over 50 % degradation after six weeks in soil. These results suggest that incorporating SA into RP composites enhances their functionality without compromising biodegradability, offering a promising solution for sustainable packaging. As regulatory bodies emphasize resource management and waste reduction, the potential of these innovative and environmentally friendly packaging solutions becomes increasingly significant.

Vanillin-crosslinked gelatin-polyvinyl alcohol aerogels: Improved physicochemical properties and antimicrobial activity

Crosslinking is a promising way to fabricate high-performance aerogels. In this study, vanillin (Van) crosslinked gelatin–polyvinyl alcohol (Gel−PVA) aerogels were prepared by vacuum freeze-drying method. The effects of different addition levels of Van on FTIR spectra, microstructures and physicochemical properties including water stability, mechanical properties, thermal stability and thermal insulation properties of aerogels were characterized, and antimicrobial activity of aerogels were validated. The results showed that Van exerted its crosslinking function through Schiff base bonding with Gel and hydrogen bonding with Gel and PVA. Although Van addition caused a slight decline in the thermal insulation performance and the obvious increase in pore diameter of aerogels, moderate Van crosslinking contributed to water stability, mechanical properties and thermal stability of aerogels. Besides, Van crosslinked Gel−PVA aerogel could effectively inhibit the growth of E. coli and B. cinerea. This suggests that the aerogel has promising applications in antimicrobial food packaging.

Effect of Strain Rate on the Structure Properties of Silica Aerogel

Silica aerogel is a versatile material used in adsorption, filtration, and thermal insulation. However, its mechanical strength is a notable weakness, making it prone to damage. This study utilized molecular dynamics simulations to investigate the mechanical properties of aerogels. We compared the simulation results with the data from the experiments. The dimensionless specific surface areas of both are nearly identical at densities below 0.7 g/cm³. We explored the impact of strain rate on aerogel properties. The compression rate had minimal effects on stress and density during uniaxial compression. The specific surface area exhibited an initial increase followed by a decrease with a rising compression rate, peaking at 2 1/ns. Furthermore, we determined the solid thermal conductivity of the aerogel, which was 0.0764 W/(m·K) without strain. The solid thermal conductivity showed little variation with compression rate but was highly sensitive to density. The stretching rate during uniaxial stretching influenced the heat transfer coefficient, density, specific surface area, and stress. However, in the low-strain region (strain < 0.3), the tensile rate had a negligible impact on these performance metrics. This investigation offers a theoretical analysis of the mechanical properties of aerogels, establishing a foundational understanding of their efficient application.

Removal of malachite green in wastewater and its mechanism by three-dimensional graphene oxide-based aerogels

Malachite green (MG) is a significant water pollutant due to its widespread use and harmful properties, making its effective removal crucial. Graphene oxide (GO) has emerged as a promising material for dye adsorption. Doping GO into cellulose aerogels enhances mechanical properties and prevents GO dissolution. Many reports claim the advantages of GO in adsorption, but challenges remain in understanding and optimizing the adsorption of MG in three-dimensional cellulosic GO (CLGO) aerogels. In this study, three-dimensional CLGO aerogels were prepared using the freeze-drying method. They achieved an MG maximum adsorption capacity of 33.98 mg g−1, and the adsorbent still had 97.04 % adsorption capacity at the seventh adsorption–desorption cycle. The photothermal properties of the CLGO aerogels were also studied, contributing to the development of the zero-liquid discharge (ZLD) post-processing concept. Molecular force field simulations indicated that π-π interaction is the primary force between MG and CLGO aerogels in the absorption process. We believe our research will guide the future optimization of MG specialized absorbent.

A Building Information Modeling driven approach for improving building envelope energy efficiency in hot arid climates

As a response to growing energy demand and greenhouse gas emissions, enhancing the energy performance of buildings has become a global focus. Studies have shown that building openings are responsible for 40–50% of their energy loss, and these percentages are growing steadily. Silica aerogel represents a potential energy-saving technology for buildings. It has demonstrated its effectiveness as an insulating material in various climates; especially cold climates, however its success in hot arid climates has not been examined yet. Therefore, this paper aims to assess the thermal properties of silica aerogel to determine the dominant parameters that impact its thermal performance in a hot, arid climate. A numerical model of the silica aerogel is conducted using Autodesk Ecotect Analysis. The impact of different factors (thermal conductivity, density, specific heat, and thickness of silica aerogel) on the energy efficiency of the glass window was investigated. Results show that the thickness of silica aerogel has the highest impact on the thermal behavior of silica aerogel, followed by thermal conductivity. Meanwhile, density and specific heat showed a negligible effect on the energy performance of the material. Results showed that a 5 mm-thick aerogel layer and a thermal conductivity of 0.014 W/(mK) exploit the energy performance of the proposed material in hot, arid climates and could provide energy savings of around 63% and 15% in heating and cooling demands, respectively.