Ultralight and fire-resistant ceramic nanofibrous aerogels with temperature-invariant superelasticity

Strong and Fatigue-Resistant Carbon Nanotube Composites Enabled by Amorphous/Crystalline Heterophase Shell

Lightweight materials with high strength and long cyclic lifespan are greatly demanded in practical applications, yet these properties are usually mutually exclusive. Here, we present a strong, lightweight, highly deformation-tolerant, and fatigue-resistant carbon nanotube (CNT) composite enabled by an amorphous/crystalline heterophase carbon shell. In particular, we obtain nanocrystallites with CNT-induced crystalline orientation uniformly embedded within an amorphous matrix by controlled thermal annealing. The heterophase carbon shell effectively alleviates the stress concentration and inhibits crack propagation, which renders our composite superior mechanical properties and high fatigue resistance (106 compression cycles at 20% strain with high stress of 144 kPa, or 5 × 105 cycles at 50% strain with stress up to 260 kPa). This study provides a deep understanding of amorphous-crystalline phase transition and insight into utilizing phase engineering to design and develop other high-performance functional materials such as structural materials and catalysis.

Bio-Informed Porous Mineral-Based Composites

Certain biominerals, such as sea sponges and echinoderm skeletons, display a fascinating combination of mechanical properties and adaptability due to the well-defined structures spanning various length scales. These materials often possess high density normalized mechanical properties because they contain well-defined pores. The density-normalized mechanical properties of synthetic minerals are often inferior because the pores are stochastically distributed, resulting in an inhomogeneous stress distribution. The mechanical properties of synthetic materials are limited by the degree of structural and compositional control currently available fabrication methods offer. In the first part of this review, examples of structural elements nature uses to impart exceptional density normalized Young's moduli to its porous biominerals are showcased. The second part highlights recent advancements in the fabrication of bio-informed mineral-based composites possessing pores with diameters that span a wide range of length scales. The influence of the processing of mineral-based composites on their structures and mechanical properties is summarized. Thereby, it is aimed at encouraging further research directed to the sustainable, energy-efficient fabrication of synthetic lightweight yet stiff mineral-based composites.

Rapid and inexpensive synthesis of liter-scale SiC aerogels

Ceramic aerogels are promising materials for thermal insulation and protection under harsh environments. Yet current synthesis methods fail to provide an energy-, time-, and cost-effective route for high-throughput production and large-scale applications, especially for non-oxide ceramic aerogels. Here we reported a way to synthesize SiC aerogels within seconds and over liter scale, with a demonstrated throughput of ~16 L min-1 in a typical lab experiment. The key lies in renovated combustion synthesis and a fast expansion from powder reactants to aerogel products over 1000% in volume. The synthesis process is self-sustainable and requires minimal energy input. The product is very cheap, with an estimated price of ~$0.7 L-1 (~$7 kg-1). The obtained SiC aerogels have excellent thermo-mechanical properties, including low thermal conductivity, high elasticity, and damage tolerance. Our invention not only offers a practical pathway for large-scale applications of ceramic aerogels, but also calls for rethinking of combustion synthesis in one-step conversion from raw chemicals to bulk products ready for practical applications.

A robust polyaniline hydrogel electrode enables superior rate capability at ultrahigh mass loadings

Simultaneously achieving high mass loading and superior rate capability in electrodes is challenging due to their often mutually constrained nature, especially for pseudocapacitors for high-power density applications. Here, we report a robust porous polyaniline hydrogel (PPH) prepared using a facile ice-templated in situ polymerization approach. Owing to the conductive, robust, and porous nanostructures suitable for ultrafast electron and ion transport, the self-supporting pure polyaniline hydrogel electrode exhibits superior areal capacitance without sacrificing rate capability and gravimetric capacitance at an ultrahigh mass loading and notable current density. It achieves a high areal capacitance (15.2 F·cm-2 at 500 mA·cm-2) and excellent rate capability (~92.7% retention from 20 to 500 mA·cm-2) with an ultrahigh mass loading of 43.2 mg cm-2. Our polyaniline hydrogel highlights the potential of designing porous nanostructures to boost the performance of electrode materials and inspires the development of other ultrafast pseudocapacitive electrodes with ultrahigh loadings and fast charge/discharge capabilities.

Elastic SiC Aerogel for Thermal Insulation: A Systematic Review

SiC aerogels with their lightweight nature and exceptional thermal insulation properties have emerged as the most ideal materials for thermal protection in hypersonic vehicles; However, conventional SiC aerogels are prone to brittleness and mechanical degradation when exposed to complex loads such as shock and mechanical vibration. Hence, preserving the structural integrity of aerogels under the combined influence of thermal and mechanical external forces is crucial not only for stabling their thermal insulation performance but also for determining their practicality in harsh environments. This review focuses on the optimization of design based on the structure-performance of SiC aerogels, providing a comprehensive review of the inherent correlations among structural stability, mechanical properties, and insulation performance. First, the thermal transfer mechanism of aerogels from a microstructural perspective is studied, followed by the relationship between the building blocks of SiC aerogels (0D particles, 1D nanowires/nanofibers) and their compression performance (including compressive resilience, compressive strength, and fatigue resistance). Moreover, the strategy to improve the high-temperature oxidation resistance and insulation performance of SiC aerogels is explored. Lastly, the challenges and future breakthrough directions for SiC aerogels are presented.

Multiphase Symbiotic Engineered Elastic Ceramic-Carbon Aerogels with Advanced Thermal Protection in Extreme Oxidative Environments

Elastic aerogels can dissipate aerodynamic forces and thermal stresses by reversible slipping or deforming to avoid sudden failure caused by stress concentration, making them the most promising candidates for thermal protection in aerospace applications. However, existing elastic aerogels face difficulties achieving reliable protection above 1500 °C in aerobic environments due to their poor thermomechanical stability and significantly increased thermal conductivity at elevated temperatures. Here, a multiphase sequence and multiscale structural engineering strategy is proposed to synthesize mullite-carbon hybrid nanofibrous aerogels. The heterogeneous symbiotic effect between components simultaneously inhibits ceramic crystalline coarsening and carbon thermal etching, thus ensuring the thermal stability of the nanofiber building blocks. Efficient load transfer and high interfacial thermal resistance at crystalline-amorphous phase boundaries on the microscopic scale, coupled with mesoscale lamellar cellular and locally closed-pore structures, achieve rapid stress dissipation and thermal energy attenuation in aerogels. This robust thermal protection material system is compatible with ultralight density (30 mg cm-3), reversible compression strain of 60%, extraordinary thermomechanical stability (up to 1600 °C in oxidative environments), and ultralow thermal conductivity (50.58 mW m-1 K-1 at 300 °C), offering new options and possibilities to cope with the harsh operating environments faced by space exploration.

Highly Flexible and Superelastic Graphene Nanofibrous Aerogels for Intelligent Sign Language

Highly flexible and superelastic aerogels at large deformation have become urgent mechanical demands in practical uses, but both properties are usually exclusive. Here a trans-scale porosity design is proposed in graphene nanofibrous aerogels (GNFAs) to break the trade-off between high flexibility and superelasticity. The resulting GNFAs can completely recover after 1000 fatigue cycles at 60% folding strain, and notably maintain excellent structural integrity after 10000 cycles at 90% compressive strain, outperforming most of the reported aerogels. The mechanical robustness is demonstrated to be derived from the trans-scale porous structure, which is composed of hyperbolic micropores and porous nanofibers to enable the large elastic deformation capability. It is further revealed that flexible and superelastic GNFAs exhibit high sensitivity and ultrastability as an electrical sensors to detect tension and flexion deformation. As proof, The GNFA sensor is implemented onto a human finger and achieves the intelligent recognition of sign language with high accuracy by multi-layer artificial neural network. This study proposes a highly flexible and elastic graphene aerogel for wearable human-machine interfaces in sensor technology.

3D-Printed Mullite-Reinforced SiC-Based Aerogel Composites

There is a growing demand for thermal management materials in electronic fields. Aerogels have attracted interest due to their extremely low density and extraordinary thermal insulation properties. However, the application of aerogels is limited by high production costs and the requirement that aerogel structures not be load-bearing. In this study, mullite-reinforced SiC-based aerogel composite (MR-SiC AC) is prepared through 3D printing combined with in situ growth of SiC nanowires in post processing. The fabricated MR-SiC AC not only has ultra-low thermal conductivity (0.021 W K m-1) and high porosity (90.0%), but also a high Young's modulus (24.4 MPa) and high compressive strength (1.65 MPa), both exceeding the measurements of existing resilient aerogels by an order of magnitude. These properties make MR-SiC AC an ideal solution for the precision thermal management of lightweight structures having complex geometry for functional devices.

Ultrathin aerogel-structured micro/nanofiber metafabric via dual air-gelation synthesis for self-sustainable heating

Incorporating passive heating structures into personal thermal management technologies could effectively mitigate the escalating energy crisis. However, current passive heating materials struggle to balance thickness and insulating capability, resulting in compromised comfort, space efficiency, and limited thermoregulatory performance. Here, a dual air-gelation strategy, is developed to directly synthesize ultrathin and self-sustainable heating metafabric with 3D dual-network structure during electrospinning. Controlling the interactions among polymer, solvent, and water enables the microphase separation of charged jets, while adjusting the distribution of carbon black nanoparticles within charged fluids to form fibrous networks composed of interlaced aerogel micro/nanofibers with heat storage capabilities. With a low thickness of 0.18 mm, the integrated metafabric exhibits exceptional thermal insulation performance (15.8 mW m-1K-1), superhydrophobicity, enhanced mechanical properties, and high breathability while maintaining self-sustainable radiative heating ability (long-lasting warming of 8.8 °C). This strategy provides rich possibilities to develop advanced fibrous materials for smart textiles and thermal management.

A flexible precontact CNT-Al2O3 fiber sensor resistant to extreme temperatures

As a new soft electronic product, a flexible precontact sensor provides spatial position sensing ability. However, the properties of traditional polymer materials change in industrial environments with extreme temperatures, which can cause the sensor function to decline or even fail. In this study, we propose a flexible fiber sensor based on the capacitor principle, which achieves a stable spatial positioning function and is not affected by a wide range of temperature changes. The fiber element of the sensor is obtained through the deposition of a flexible Al2O3 ceramic coating onto the surface of a carbon nanotube fiber (CNTF) via atomic layer deposition (ALD) technology. Coatings of different thicknesses (100 nm, 200 nm, and 300 nm) show different colors. The temperature resistance and flame retardancy of Al2O3 keep the morphology of the composite fiber unaffected by flame or high temperatures. Even at extreme temperatures (-78 °C to 500 °C), the sensor's sensing ability exhibits excellent stability. In addition, the spatial perception of the fibers remained viable after repeated bending (10 000 times). We demonstrate the potential of the sensor to acquire position information during high-temperature industrial pipe docking.

TiO2/SiO2 spiral crimped Janus fibers engineered for stretchable ceramic membranes with high-temperature resistance

The tensile brittleness of ceramic nanofibrous materials makes them unable to withstand the relatively large fracture strain, greatly limiting their applications in extreme environments such as high or ultra-low temperatures. Herein, highly stretchable and elastic ceramic nanofibrous membranes composed of titanium dioxide/silicon dioxide (TiO2/SiO2) bicomponent spiral crimped Janus fibers were designed and synthesized via conjugate electrospinning combined with calcination treatment. Owing to the opposite charges attached, the two fibers assembled side by side to form a Janus structure. Interestingly, radial shrinkage differences existed on the two sides of the TiO2/SiO2 composite nanofibers, constructing a helical crimp structure along the fiber axis. The special configuration effectively improves the stretchability of TiO2/SiO2 ceramic nanofibrous membranes, with up to 70.59% elongation at break, excellent resilience at 20% tensile strain and plastic deformation of only 3.48% after 100 cycles. Additionally, the relatively fluffy ceramic membranes constructed from spiral crimped Janus fibers delivered a lower thermal conductivity of 0.0317 W m-1 K-1, attributed to the increased internal still air content. This work not only reveals the attractive tensile mechanism of ceramic membranes arising from the highly curly nanofibers, but also proposes an effective strategy to make the ceramic materials withstand the complex dynamic strain in extreme temperature environments (from -196 °C to 1300 °C).

High-Performance Multifunctional Carbon Fibrous Sponges Derived from Pitch

3D carbon-based porous sponges are recognized for significant potential in oil absorption and electromagnetic interference (EMI). However, their widespread application is hindered by a common compromise between high performance and affordability of mass production. Herein, a novel approach is introduced that involves laser-assisted micro-zone heating melt-blown spinning (LMHMS) to address this challenge by creating pitch-based submicron carbon fibers (PSCFs) sponge with 3D interconnected structures. These structures bestow the resulting sponge exceptional characteristics including low density (≈20 mg cm-3), high porosity (≈99%), remarkable compressibility (80% maximum strain), and superior conductivity (≈628 S m-1). The resultant PSCF sponges realize an oil/organic solvent sorption capacity over 56 g/g and possess remarkable regenerated ability. In addition to their effectiveness in cleaning up oil/organic solvent spills, they also demonstrated strong electromagnetic shielding capabilities, with a total shielding effectiveness (SE) exceeding 60 dB across the X-band GHz range. In virtue of extreme lightweight of ≈20 mg cm-3, the specific SE of the PSCF sponge reaches as high as ≈1466 dB cm3 g-1, surpassing the performance of numerous carbon-based porous structures. Thus, the unique blend of properties renders these sponges promising for transforming strategies in addressing oil/organic solvent contaminations and providing effective protection against EMI.

Tailoring Mechanical Properties of a Ceramic Nanowire Aerogel with Pyrolytic Carbon for In Situ Resilience at 1400 °C

Resilient ceramic aerogels with a unique combination of lightweight, good high-temperature stability, high specific area, and thermal insulation properties are known for their promising applications in various fields. However, the mechanical properties of traditional ceramic aerogels are often constrained by insufficient interlocking of the building blocks. Here, we report a strategy to largely increase the interlocking degree of the building blocks by depositing a pyrolytic carbon (PyC) coating onto Si3N4 nanowires. The results show that the mechanical performances of the Si3N4 nanowire aerogels are intricately linked to the microstructure of the PyC nodes. The compression resilience of the Si3N4@PyC nanowire aerogels increases with an increase of the interlayer cross-linking in PyC. Additionally, benefiting from the excellent high-temperature stability of PyC, the Si3N4@PyC nanowire aerogels demonstrate significantly superior in situ resilience up to 1400 °C. The integrated mechanical and high-temperature properties of the Si3N4@PyC nanowire aerogels make them highly appealing for applications in harsh conditions. The facile method of manipulating the microstructure of the nodes may offer a perspective for tailoring the mechanical properties of ceramic aerogels.

Preparation of Fibrous Three-Dimensional Porous Materials and Their Research Progress in the Field of Stealth Protection

Intelligent and diversified development of modern detection technology greatly affects the battlefield survivability of military targets, especially infrared, acoustic wave, and radar detection expose targets by capturing their unavoidable infrared radiation, acoustic wave, and electromagnetic wave information, greatly affecting their battlefield survival and penetration capabilities. Therefore, there is an urgent need to develop stealth-protective materials that can suppress infrared radiation, reduce acoustic characteristics, and weaken electromagnetic signals. Fibrous three-dimensional porous materials, with their high porosity, excellent structural adjustability, and superior mechanical properties, possess strong potential for development in the field of stealth protection. This article introduced and reviewed the characteristics and development process of fibrous three-dimensional porous materials at both the micrometer and nanometer scales. Then, the process and characteristics of preparing fibrous three-dimensional porous materials through vacuum forming, gel solidification, freeze-casting, and impregnation stacking methods were analyzed and discussed. Meanwhile, their current application status in infrared, acoustic wave, and radar stealth fields was summarized and their existing problems and development trends in these areas from the perspectives of preparation processes and applicability were analyzed. Finally, several prospects for the current challenges faced by fibrous three-dimensional porous materials were proposed as follows: functionally modifying fibers to enhance their applicability through self-cross-linking; establishing theoretical models for the transmission of thermal energy, acoustic waves, and electromagnetic waves within fibrous porous materials; constructing fibrous porous materials resistant to impact, shear, and fracture to meet the needs of practical applications; developing multifunctional stealth fibrous porous materials to confer full-spectrum broadband stealth capability; and exploring the relationship between material size and mechanical properties as a basis for preparing large-scale samples that meet the application's requirement. This review is very timely and aims to focus researchers' attention on the importance and research progress of fibrous porous materials in the field of stealth protection, so as to solve the problems and challenges of fibrous porous materials in the field of stealth protection and to promote the further innovation of fibrous porous materials in terms of structure and function.

Building-Envelope-Inspired, Thermomechanically Robust All-Fiber Ceramic Meta-Aerogel for Temperature-Controlled Dominant Infrared Camouflage

The unsatisfactory properties of ceramic aerogels when subjected to thermal shock, such as strength degradation and structural collapse, render them unsuitable for use at large thermal gradients or prolonged exposure to extreme temperatures. Here, a building-envelope-inspired design for fabricating a thermomechanically robust all-fiber ceramic meta-aerogel with interlocked fibrous interfaces and an interwoven cellular structure in the orthogonal directions is presented, which is achieved through a two-stage physical and chemical process. Inspired by the reinforced concrete building envelope, a solid foundation composed of fibrous frames is constructed and enhanced through supramolecular in situ self-assembly to achieve high compressibility, retaining over 90% of maximum stress under a considerable compressive strain of 50% for 10 000 cycles, and showing temperature-invariance when compressed at 60% strain within the range of -100 to 500 °C. As a result of its distinct response to oscillation tolerance coupled with elastic recovery, the all-fiber ceramic meta-aerogel exhibits exceptional suitability for thermal shock resistance and infrared camouflage performance in cold (-196 °C) and hot (1300 °C) fields. This study provides an opportunity for developing ceramic aerogels for effective thermal management under extreme conditions.

Biodegradable Honeycomb-Mimic Scaffolds Consisting of Nanofibrous Walls

The scaffold is a porous three-dimensional (3D) material that supports cell growth and tissue regeneration. Such 3D structures should be generated with simple techniques and nontoxic ingredients to mimic bio-environment and facilitate tissue regeneration. In this work, simple but powerful techniques are demonstrated for the fabrication of lamellar and honeycomb-mimic scaffolds with poly(L-lactic acid). The honeycomb-mimic scaffolds with tunable pore size ranging from 70 to 160 µm are fabricated by crystal needle-guided thermally induced phase separation in a directional freezing apparatus. The compressive modulus of the honeycomb-mimic scaffold is ≈4 times higher than that of scaffold with randomly oriented pore structure. The fabricated honeycomb-mimic scaffold exhibits a hierarchical structure from nanofibers to micro-/macro-tubular structures. Pre-osteoblast MC3T3-E1 cells cultured on the honeycomb-mimic nanofibrous scaffolds exhibit an enhanced osteoblastic phenotype, with elevated expression levels of osteogenic marker genes, than those on either porous lamellar scaffolds or porous scaffolds with randomly oriented pores. The advanced techniques for the fabrication of the honeycomb-mimic structure may potentially be used for a wide variety of advanced functional materials.

Integrated Firefighting Textile with Temperature and Pressure Monitoring for Personal Defense

Although electronic textiles that can detect external stimuli show great promise for fire rescue, existing firefighting clothing is still scarce for simultaneously integrating reliable early fire warning and real-time motion sensing, hardly providing intelligent personal protection under complex high-temperature conditions. Herein, we introduce an "all-in-one" hierarchically sandwiched fabric (HSF) sensor with a simultaneous temperature and pressure stimulus response for developing intelligent personal protection. A cross-arranged structure design has been proposed to tackle the serious mutual interference challenge during multimode sensing using two separate sets of core-sheath composite yarns and arrayed graphene-coated aerogels. The functional design of the HSF sensor not only possesses wide-range temperature sensing from 25 to 400 °C without pressure disturbance but also enables highly sensitive pressure response with good thermal adaptability (up to 400 °C) and wide pressure detection range (up to 120 kPa). As a proof of concept, we integrate large-scalable HSF sensors onto conventional firefighting clothing for passive/active fire warning and also detecting spatial pressure and temperature distribution when a firefighter is exposed to high-temperature flames, which may provide a useful design strategy for the application of intelligent firefighting protective clothing.

A Biomimetic Cement-Based Solid-State Electrolyte with Both High Strength and Ionic Conductivity for Self-Energy-Storage Buildings

Cement-based materials are the foundation of modern buildings but suffer from intensive energy consumption. Utilizing cement-based materials for efficient energy storage is one of the most promising strategies for realizing zero-energy buildings. However, cement-based materials encounter challenges in achieving excellent electrochemical performance without compromising mechanical properties. Here, we introduce a biomimetic cement-based solid-state electrolyte (labeled as l-CPSSE) with artificially organized layered microstructures by proposing an in situ ice-templating strategy upon the cement hydration, in which the layered micropores are further filled with fast-ion-conducting hydrogels and serve as ion diffusion highways. With these merits, the obtained l-CPSSE not only presents marked specific bending and compressive strength (2.2 and 1.2 times that of traditional cement, respectively) but also exhibits excellent ionic conductivity (27.8 mS·cm-1), overwhelming most previously reported cement-based and hydrogel-based electrolytes. As a proof-of-concept demonstration, we assemble the l-CPSSE electrolytes with cement-based electrodes to achieve all-cement-based solid-state energy storage devices, delivering an outstanding full-cell specific capacity of 72.2 mF·cm-2. More importantly, a 5 × 5 cm2 sized building model is successfully fabricated and operated by connecting 4 l-CPSSE-based full cells in series, showcasing its great potential in self-energy-storage buildings. This work provides a general methodology for preparing revolutionary cement-based electrolytes and may pave the way for achieving zero-carbon buildings.

Advancements in Thermal Insulation through Ceramic Micro-Nanofiber Materials

Ceramic fibers have the advantages of high temperature resistance, light weight, favorable chemical stability and superior mechanical vibration resistance, which make them widely used in aerospace, energy, metallurgy, construction, personal protection and other thermal protection fields. Further refinement of the diameter of conventional ceramic fibers to microns or nanometers could further improve their thermal insulation performance and realize the transition from brittleness to flexibility. Processing traditional two-dimensional (2D) ceramic fiber membranes into three-dimensional (3D) ceramic fiber aerogels could further increase porosity, reduce bulk density, and reduce solid heat conduction, thereby improving thermal insulation performance and expanding application areas. Here, a comprehensive review of the newly emerging 2D ceramic micro-nanofiber membranes and 3D ceramic micro-nanofiber aerogels is demonstrated, starting from the presentation of the thermal insulation mechanism of ceramic fibers, followed by the summary of 2D ceramic micro-nanofiber membranes according to different types, and then the generalization of the construction strategies for 3D ceramic micro-nanofiber aerogels. Finally, the current challenges, possible solutions, and future prospects of ceramic micro-nanofiber materials are comprehensively discussed. We anticipate that this review could provide some valuable insights for the future development of ceramic micro-nanofiber materials for high temperature thermal insulation.

High-Energy Laser Protection Performance of Fibrous Felt-Reinforced Aerogels with Hierarchical Porous Architectures

Continuous-wave lasers can cause irreversible damage to structured materials in a very short time. Modern high-energy laser protection materials are mainly constructed from ceramic, polymer, and metal constitutions. However, these materials are protected by sacrificing their structural integrity under the irradiation of high-energy lasers. In this contribution, we reported multilayer fibrous felt-reinforced aerogels that can sustain the continuous irradiation of a laser at a power density of 120 MW·m-2 without structural damage. It is found that the exceptional high-energy laser protection performance and the comparable mechanical properties of aerogel nanocomposites are attributed to the unique characteristics of hierarchical porous architectures. In comparison with various preparation methods and other aerogel materials, multilayer fibrous felt-reinforced aerogels exhibit the best performance in high-energy laser protection, arising from the gradual interception and the Raman-Rayleigh scattering cycles of a high-energy laser in the porous aerogels. Furthermore, a near-zero thermal expansion coefficient and extremely low thermal conductivity at high temperature allow the lightweight felt-reinforced aerogels to be applied in extreme conditions. The felt-reinforced aerogels reported herein offer an attractive material that can withstand complex thermomechanical stress and retain excellent insulation properties at extremely high temperature.

Fast Solution Blow Spinning of Lotus-Leaf-Inspired SiO2 Nanofiber Sponge for High Efficiency Purification

Massive production of SiO2 nanofibers with both high durability and exceptional performance remains a significant challenge. Herein, a novel approach was introduced to achieve the massive production of SiO2 nanofibers with lotus-leaf-inspired surfaces by combining solution blowing spinning (SBS) and the polymer-derived ceramics method. Based on the SBS technique, three types of precursor nanofiber products were fast spined with methyl silsesquioxane polymer and polymethyl hydrogen siloxane employed as Si sources. The flow rate of the SBS spined Si-based ceramic nanofibers was enhanced to 20 mL·h-1. Furthermore, through the integration of hydrophobic-oleophilic SiO2 nanoparticles into the precursor solution, SiO2 nanofibers with lotus-leaf nanoprotrusion surfaces were fabricated. Nanoparticle-decorated SiO2 fibers demonstrated excellent hydrophobicity (138.3°), compression resilience (∼60%), proficiency in organic pollutant adsorption, high-temperature resistance (∼1100 °C), and outstanding thermal insulation properties (thermal conductivity of 0.0165 W·(m·K)-1).

Way to a Library of Ti-Series Oxide Nanofiber Sponges that are Highly Stretchable, Compressible, and Bendable

Ti-series oxide ceramics in the form of aerogels, such as TiO2, SrTiO3, BaTiO3, and CaCu3Ti4O12, hold tremendous potential as functional materials owing to their excellent optical, dielectric, and catalytic properties. Unfortunately, these inorganic aerogels are usually brittle and prone to pulverization owing to weak inter-particulate interactions, resulting in restricted application performance and serious health risks. Herein, a novel strategy is reported to synthesize an elastic form of an aerogel-like, highly porous structure, in which activity-switchable Ti-series oxide sols transform from the metastable state to the active state during electrospinning, resulting in condensation and solidification at the whipping stage to obtain curled nanofibers. These curled nanofibers are further entangled when flying in the air to form a physically interlocked, elastic network mimicking the microstructure of high-elasticity hydrogels. This strategy provides a library of Ti-series oxide nanofiber sponges with unprecedented stretchability, compressibility, and bendability, possessing extensive opportunities for greener, safer, and broader applications as integrated or wearable functional devices. As a proof-of-concept demonstration, a new, elastic form of TiO2, composed of both "white" and "black" TiO2 nanofiber sponges, is constructed as spontaneous air-conditioning textiles in smart clothing, buildings, and vehicles, with unique bidirectional regulation of radiative cooling in summer and solar heating in winter.

Beyond the limiting gap length: peripheral nerve regeneration through implantable nerve guidance conduits

Peripheral nerve damage results in the loss of sensorimotor and autonomic functions, which is a significant burden to patients. Furthermore, nerve injuries greater than the limiting gap length require surgical repair. Although autografts are the preferred clinical choice, their usage is impeded by their limited availability, dimensional mismatch, and the sacrifice of another functional donor nerve. Accordingly, nerve guidance conduits, which are tubular scaffolds engineered to provide a biomimetic environment for nerve regeneration, have emerged as alternatives to autografts. Consequently, a few nerve guidance conduits have received clinical approval for the repair of short-mid nerve gaps but failed to regenerate limiting gap damage, which represents the bottleneck of this technology. Thus, it is still necessary to optimize the morphology and constituent materials of conduits. This review summarizes the recent advances in nerve conduit technology. Several manufacturing techniques and conduit designs are discussed, with emphasis on the structural improvement of simple hollow tubes, additive manufacturing techniques, and decellularized grafts. The main objective of this review is to provide a critical overview of nerve guidance conduit technology to support regeneration in long nerve defects, promote future developments, and speed up its clinical translation as a reliable alternative to autografts.

Robust and Flame-Retardant Zylon Aerogel Fibers for Wearable Thermal Insulation and Sensing in Harsh Environment

The exceptional lightweight, highly porous, and insulating properties of aerogel fibers make them ideal for thermal insulation. However, current aerogel fibers face limitations due to their low resistance to harsh environments and a lack of intelligent responses. Herein, a universal strategy for creating polymer aerogel fibers using crosslinked nanofiber building blocks is proposed. This approach combines controlled proton absorption gelation spinning with a heat-induced crosslinking process. As a proof-of-concept, Zylon aerogel fibers that exhibited robust thermal stability (up to 650 °C), high flame retardancy (limiting oxygen index of 54.2%), and extreme chemical resistance are designed and synthesized. These fibers possess high porosity (98.6%), high breaking strength (8.6 MPa), and low thermal conductivity (0.036 W m-1 K-1 ). These aerogel fibers can be knotted or woven into textiles, utilized in harsh environments (-196-400 °C), and demonstrate sensitive self-powered sensing capabilities. This method of developing aerogel fibers expands the applications of high-performance polymer fibers and holds great potential for future applications in wearable smart protective fabrics.

Multiscale Interpenetrated/Interconnected Network Design Confers All-Carbon Aerogels with Unprecedented Thermomechanical Properties for Thermal Insulation under Extreme Environments

With ultralight weight, low thermal conductivity, and extraordinary high-temperature resistance, carbon aerogels hold tremendous potential against severe thermal threats encountered by hypersonic vehicles during the in-orbit operation and re-entry process. However, current 3D aerogels are plagued by irreconcilable contradictions between adiabatic and mechanical performance due to monotonicity of the building blocks or uncontrollable assembly behavior. Herein, a spatially confined assembly strategy of multiscale low-dimensional nanocarbons is reported to decouple the stress and heat transfer. The nanofiber framework, a basis for transferring the loading strain, is covered by a continuous thin-film-like layer formed by the aggregation of nanoparticles, which in combination serve as the fundamental structural units for generating an elastic behavior while yielding compartments in aerogels to suppress the gaseous fluid thermal diffusion within distinct partitions. The resulting all-carbon aerogels with a hierarchical cellular structure and quasi-closed cell walls achieve the best thermomechanical and insulation trade-off, exhibiting flyweight density (24 mg cm-3 ), temperature-constant compressibility (-196-1600 °C), and a low thermal conductivity of 0.04 829 W m-1 K-1 at 300 °C. This strategy provides a remarkable thermal protection material in hostile environments for future aerospace exploration.

Direct synthesis of ultralight, elastic, high-temperature insulation N-doped TiO2 ceramic nanofibrous sponges via conjugate electrospinning

The design of three-dimensional ceramic nanofibrous materials with high-temperature insulation and flame-retardant characteristics is of significant interest due to the effectively improved mechanical properties. However, achieving a pure ceramic monolith with ultra-low density, high elasticity and toughness remains a great challenge. Herein, a low-cost, scalable strategy to fabricate ultralight and mechanically robust N-doped TiO2 ceramic nanofibrous sponges with a continuous stratified structure by conjugate electrospinning is reported. Remarkably, the introduction of dopamine into the precursor nanofibers is engineered, which realizes the nitrogen doping to inhibit the TiO2 grain growth, endowing single nanofibers with a smoother, less defective surface. Besides, the self-polymerization process of dopamine allows the construction of bonding points between nanofibers and optimizes the distribution of inorganic micelles on polymer templates. Moreover, a rotating disk receiving device under different rotating speeds is designed to obtain N-doped TiO2 sponges with various interlamellar spacings, further affecting the maximum compressive deformation capacity. The resulting ceramic sponges, consisting of fluffy crosslinked nanofiber layers, possess low densities of 12-45 mg cm-3, which can quickly recover under a large strain of 80% and have only 9.2% plastic deformation after 100 compression cycles. In addition, the sponge also exhibits a temperature-invariant superelasticity at 25-800 °C and a low heat conductivity of 0.0285 W m-1 K-1, with an outstanding thermal insulation property, making it an ideal insulation material for high-temperature or harsh conditions.

Biomimetic Bouligand chiral fibers array enables strong and superelastic ceramic aerogels

Ceramic aerogels are often used when thermal insulation materials are desired; however, they are still plagued by poor mechanical stability under thermal shock. Here, inspired by the dactyl clubs of mantis shrimp found in nature, which form by directed assembly into hierarchical, chiral and Bouligand (twisted plywood) structure exhibiting superior mechanical properties, we present a compositional and structural engineering strategy to develop strong, superelastic and fatigue resistance ceramic aerogels with chiral fibers array resembling Bouligand architecture. Benefiting from the stress dissipation, crack torsion and mechanical reinforcement of micro-/nano-scale Bouligand array, the tensile strength of these aerogels (170.38 MPa) is between one and two orders of magnitude greater than that of state-of-the-art nanofibrous aerogels. In addition, the developed aerogels feature low density and thermal conductivity, good compressive properties with rapid recovery from 80 % strain, and thermal stability up to 1200 °C, making them ideal for thermal insulation applications.

Ultrastrong lightweight nanocellulose-based composite aerogels with robust superhydrophobicity and durable thermal insulation under extremely environment

Ultra-lightweight porous aerogels based on nanocellulose (NC) have promising applications in various fields such as building insulation, sewage treatment, energy storage, and aerospace. One of the key advantages of these aerogels is their exceptionally low thermal conductivity. Nevertheless, the thermal insulation of NC aerogel (NCA) can deteriorate with changes in temperature and humidity conditions, making it crucial to develop a bulk aerogel that can maintain exceptional thermal insulating properties in harsh environmental conditions. A sustainable and user-friendly approach to synthesizing cellulose/poly(vinyl alcohol) aerogel (CellPA) materials has been developed, which are lightweight, possess good insulating properties, and demonstrate robust superhydrophobicity even in harsh environmental conditions. The CellPA are both exceptionally lightweight and robust, boasting outstanding resistance to combustion while also displaying a thermal conductivity of 36.1 mW m-1 K-1, suggesting they hold great promise for insulation applications. Furthermore, CellPA also exhibits robust superhydrophobicity even under harsh conditions, confirming the homogenous superhydrophobic modification of the biodegradable PVA through chemical methods. The manufacturing of bio-based composite materials with enhanced mechanical and thermal insulation features has gained immense popularity in a broad spectrum of contemporary engineering applications. These composite materials are particularly valuable as a robust, energy-efficient, lightweight, waterproof and flameproof for construction materials.

Improvement strategies for oil/water separation based on electrospun SiO2 nanofibers

Oil spills and oily effluents from industry and daily life pose a great threat to all organisms in the ecosystem, while aggravating the problem of water scarcity, which has developed into a global challenge. Therefore, the development of advanced materials and technologies for oil/water separation has become a focus of attention. One-dimensional (1D) SiO2 nanofibers (SNFs) have become one of the most widely used inorganic nanomaterials in the past due to their stable chemical properties, excellent biocompatibility, and high temperature resistance etc. Meanwhile, electrospinning technique, as an emerging technology for treating oil/water emulsions, electrospun SNFs on this basis also has a number of advantages such as adjustable wettability, diverse structure and good connectivity. This review provides a systematic overview of the research progress of electrospun SNFs in different aspects. In this review, we first introduce the basic principles of electrospun SNFs, then focus on the design structures of various SNFs, propose corresponding strategies for the property improvement of SNFs, also analyze and consider the applications of SNFs. Finally, the challenges faced by electrospun SNFs in the field of oil/water separation are analyzed, and the future directions of electrospun SNFs are summarized and prospected.

Bi2O3/Gd2O3 Meta-Aerogel with Leaf-Inspired Nanotrap Array Enables Efficient X-Ray Absorption

The increasing utilization of X-rays has generated a growing need for efficient shielding materials. However, the existing Pb-based materials suffer from a narrow X-ray absorbing range, high weight, and rigidity. Inspired by the natural leaf, which can efficiently absorb light through chlorophyll and carotenoids in confined cells, we engineer ultralight and superelastic nanofibrous Bi2O3/Gd2O3 meta-aerogels (BGAs) with X-ray nanotrap arrays by manipulating the 3D confined assembly of 1D Bi2O3 and Gd2O3 nanofibers. The BGAs can synergistically absorb X-ray photons from complementary energy ranges into the nanotraps and induce cyclic collisions with Bi2O3 and Gd2O3 nanofibers, maximizing the effective X-ray attenuation. The meta-aerogel exhibits the integrated performance of efficient X-ray shielding efficiency (60-83%, 16-90 keV), ultralow density (10 mg cm-3), and superelasticity. The production of these meta-aerogels presents an avenue for the development of next-generation X-ray protective materials and the resolution of X-ray imaging systems.

Construction of Binary RGO/TiO2 Fibrous Membranes with Enhanced Mechanical Properties for E. coli Inactivation

For environmental remediation, it is significant to design membranes with good mechanical properties and excellent photocatalytic activity. In this work, RGO/TiO2 membranes with heterogeneous structures and good photocatalytic efficiency were synthesized using the method of electrospinning combined with a thermal treatment process. In the binary nanocomposites, RGO was tightly adhered to TiO2 fibers and by simply adjusting the loading of RGO, the strength and modulus of the fibrous membranes were improved. Notably, the RGO-permeated TiO2 fibers exhibited 1.41 MPa in tensile strength and 140.02 MPa in Young's modulus, which were 705% and 343% of the original TiO2 fibers, respectively. Benefiting from the enhanced light response and the homogeneous and compact heterogeneous structure, the synthesized RGO/TiO2 membranes displayed good antibacterial performance with a photocatalytic inactivation rate of 6 log against E. coli within 60 min. This study offers a highly efficient alternative to inactivate E. coli for the synthesis of TiO2-based membranes.

Engineering Covalent Heterointerface Enables Superelastic Amorphous SiC Meta-Aerogels

SiC is an exceptionally competitive material for porous ceramics owing to its excellent high-temperature mechanical stability. However, SiC porous ceramics suffer from serious structural damage and mechanical degradation under thermal shock due to the hard SiC microstructure and weak bonding networks. Here, we report a scalable interface-engineering protocol to reliably assemble flexible amorphous SiC nanofibers into lamellar cellular meta-aerogels by designing a covalent heterointerface. This approach allows the construction of a strong binding architecture within the resilient nanofiber skeleton network, thereby achieving structurally stable, mechanically robust, and durable SiC porous ceramics. The optimized amorphous SiC meta-aerogels (a-SiC MAs) exhibit the integrated properties of ultralight with a density of 4.84 mg cm-3, temperature-invariant superelastic, fatigue-resistant at low 5% permanent deformation after 1000 cycles of compression, and ultralow thermal conductivity (19 mW m-1 K-1). These characteristics provide a-SiC MAs potential application value in the thermal protection field.

Strong yet flexible ceramic aerogel

Ceramic aerogels are highly efficient, lightweight, and chemically stable thermal insulation materials but their application is hindered by their brittleness and low strength. Flexible nanostructure-assembled compressible aerogels have been developed to overcome the brittleness but they still show low strength, leading to insufficient load-bearing capacity. Here we designed and fabricated a laminated SiC-SiOx nanowire aerogel that exhibits reversible compressibility, recoverable buckling deformation, ductile tensile deformation, and simultaneous high strength of up to an order of magnitude larger than other ceramic aerogels. The aerogel also shows good thermal stability ranging from -196 °C in liquid nitrogen to above 1200 °C in butane blow torch, and good thermal insulation performance with a thermal conductivity of 39.3 ± 0.4 mW m-1 K-1. These integrated properties make the aerogel a promising candidate for mechanically robust and highly efficient flexible thermal insulation materials.

Inhibited Grain Growth Through Phase Transition Modulation Enables Excellent Mechanical Properties in Oxide Ceramic Nanofibers up to 1700 °C

Oxide ceramics are widely used as thermal protection materials due to their excellent structural properties and earth abundance. However, in extremely high-temperature environments (above 1500 °C), the explosive growth of grain size causes irreversible damage to the microstructure of oxide ceramics, thus exhibiting poor thermomechanical stability. This problem, which may lead to catastrophic accidents, remains a great challenge for oxide ceramic materials. Here, a novel strategy of phase transition modulation is proposed to control the grain growth at high temperatures in oxide ceramic nanofibers, realizing effective regulation of the crystalline forms as well as the size uniformity of primary grains, and thus suppressing the malignant growth of the grains. The resulting oxide ceramic nanofibers have excellent mechanical strength and flexibility, delivering an average tensile strength as high as 1.02 GPa after being exposed to 1700 °C for 30 min, and can withstand thousands of flexural cycles without obvious damage. This work may provide new insight into the development of advanced oxide ceramic materials that can serve in extremely high-temperature environments with long-term durability.

Meta-Aerogel Electric Trap Enables Instant and Continuable Pathogen Killing in Face Masks

The tremendous menace of the COVID-19 pandemic has underscored the urgency for antipathogen masks to stop the transmission of airborne infectious diseases. Most prevailing antipathogen masks manifest a slower sterilization rate that lags behind the pathogen momentum traversing the masks, thereby engendering an elevated susceptibility to infection. Here we tailor nanofibrous meta-aerogel electric traps, 3D-assembled from self-knotted carbon nanotube networks in an all rigid nanofibrous skeleton. This superior configuration revolves around the creation of numerous "dielectrophoretic-aerodynamic grippers", which are capable of directional manipulation of microbes toward the region of the lethal intensive electric field. Based on this, we present a disinfection unit comprising a pair of aerogel electrodes that demonstrate a rapid killing rate (>99.99% biocidal efficacy within 0.016 s) and long-term durability (12 h of continuous operation). Additionally, a microbutton lithium cell is employed as a power supply to fabricate an antipathogen face mask with this disinfection unit, which exhibits superior pathogen inactivation efficacy compared to commercial masks. This scalable biocidal protective equipment holds great potential for use in emergency medical services.

Amorphous/Nanocrystalline, Lightweight, Wave-Transparent Boron Nitride Nanobelt Aerogel for Thermal Insulation

At present, the new generation of aircraft is developing in the direction of high speed, long endurance, high mobility, and repeatability. Some studies have shown that the surface temperature of the radome can reach even 1800 °C as the flight speed of the aircraft increases. However, the antenna inside the radome cannot serve at this temperature. Consequently, a thermal insulation system with electromagnetic wave-transparent ability and high-temperature resistance is urgently needed to protect the antenna from working normally. An aerogel material is known as "solid smoke," with the lowest density currently. Because of its high porosity (>90%) and the characteristics of nanopore size, its application in the field of thermal insulation always draws the attention of researchers. In this work, a novel amorphous/nanocrystalline boron nitride (BN) nanobelt aerogel was synthesized successfully. The BN aerogel shows lightweight (18 mg/cm3), good thermal stability (1400 °C under an inert atmosphere and 750 °C under an air atmosphere), wideband wave-transparent performance (dielectric constant of 1.03 and dielectric loss of 0.016 at 4-18 GHz), and thermal insulation property (43 mW/(m·K) at room temperature and 73 mW/(m·K) at 600 °C). The BN aerogel is a suitable candidate as an electromagnetic wave-transparent thermal insulator and fire-resistant material. What is more, the structural stability of the BN aerogel is good (Young's modulus remains basically constant during the fatigue tests), and the energy loss coefficient (∼0.56) is high; it also has the potential to be a mechanical energy dissipative material. The study on the amorphous/nanocrystalline BN nanobelt aerogel provides a new idea for structure design and performance optimization of a high-temperature electromagnetic functional insulation material.

Ambient Pressure Drying of Freeze-Cast Ceramics from Aqueous Suspension

Freeze-casting has been wildly exploited to construct porous ceramics but usually requires costly and demanding freeze-drying (high vacuum, size limit, and supercooled chamber), which can be avoided by the ambient pressure drying (APD) technique. However, applying APD to freeze-cast ceramic based on an aqueous suspension is still challenging due to inert surface chemistry. Herein, a modified APD strategy is developed to improve the drying process of freeze-cast ceramics by exploiting the simultaneous ice etching, ionic cross-linking, and solvent exchange under mild conditions (-10-0 °C, ambient pressure). This versatile strategy is applicable to various ceramic species, metal ions, and freezing techniques. The incorporated metal ions not only enhance liquid-phase sintering, producing ceramics with higher density and mechanical properties than freeze-cast counterparts, but also render customizable coloration and antibacterial property. The cost-/time-efficient APD is promising for mass production and even successive production of large-size freeze-cast ceramics that exceed the size of commercial freeze-dryers.

Fiber Sedimentation and Layer-By-Layer Assembly Strategy for Designing Biomimetic Quasi-Ordered Mullite Fiber Aerogels as Extreme Conditions Thermal Insulators

Ceramic fiber aerogels are attractive thermal insulating materials. In a thermomechanical coupling environment, however, they often show limited mechanical strength and considerably increased heat transfer which can lead to thermal runaway. In this paper, inspired by bird's nest and nacre, we demonstrate a sample strategy combining fiber sedimentation and layer-by-layer assembly to fabricate ultrastrong mullite fiber aerogels (MFAs) with quasi-ordered structures. The fibrous layers and fiber bridges are constructed in a fiber sedimentation self-assembly process. The fiber sedimentation technique optimizes the structure of the MFAs by regulating the fiber orientation. Owing to the quasi-ordered structure, the fabricated MFAs exhibit the integrated properties of high compression fatigue resistance, temperature-invariant compression resilience from -196 to 1300 °C, and low thermal conductivity (0.034 W·m-1·K-1). By deliberately pressing multilayer MFAs into a thin paper, we substantially enhance the load-bearing capacity of the MFAs and achieve large temperature differences (563 °C) between the cold and hot surfaces by using a thin layer of MFAs (3-5 mm) under the simulated high-temperature (685 °C) and high-pressure (0.9 MPa) environment test. The combination of compression resistance, mechanical flexibility, and excellent thermal insulation provides an appealing material for efficient thermal insulation in extreme environments.

Chemically bonded multi-nanolayer inorganic aerogel with a record-low thermal conductivity in a vacuum

Inorganic aerogels have exhibited many superior characteristics with extensive applications, but are still plagued by a nearly century-old tradeoff between their mechanical and thermal properties. When reducing thermal conductivity by ultralow density, inorganic aerogels generally suffer from large fragility due to their brittle nature or weak joint crosslinking, while enhancing the mechanical robustness by material design and structural engineering, they easily sacrifice thermal insulation and stability. Here, we report a chemically bonded multi-nanolayer design and synthesis of a graphene/amorphous boron nitride aerogel to address this typical tradeoff to further enhance mechanical and thermal properties. Attributed to the chemically bonded interface and coupled toughening effect, our aerogels display a low density of 0.8 mg cm-3 with ultrahigh flexibility (elastic compressive strain up to 99% and bending strain up to 90%), and exceptional thermostability (strength degradation <3% after sharp thermal shocks), as well as the lowest thermal conductivities in a vacuum (only 1.57 mW m-1 K-1 at room temperature and 10.39 mW m-1 K-1 at 500°C) among solid materials to date. This unique combination of mechanical and thermal properties offers an attractive material system for thermal superinsulation at extreme conditions.

Janus Dual Self-Strengthening Structure of Bi2 O3 /Gd2 O3 Nanofibrous Membranes for Superior X-Ray Shielding

Bi2 O3 /rare earth oxide biphasic absorbers are attractive for high-efficiency X-ray shielding due to the complementary X-ray absorption effects. However, its application is severely hindered by poor interphasic contact. Here, a new Janus interface engineering strategy is reported for the construction of continuous and flexible Bi2 O3 /Gd2 O3 crystal nanofibrous membranes (FJNMs) with micro/nano dual self-strengthening interphasic adhesion. This strategy facilitates online micro-interlocking between Bi2 O3 /Gd2 O3 nanofibers and in situ nano-grain fusion between Bi2 O3 /Gd2 O3 crystals, significantly enhancing the adhesive strength at the Bi2 O3 /Gd2 O3 interface. Additionally, the synergistic shielding effect from Bi2 O3 /Gd2 O3 absorption and multiple reflections in Bi2 O3 and Gd2 O3 crystal lattices make the nanofibrous membranes a superior X-ray radiation barrier. The FJNMs demonstrate integrated features of exceptional X-ray shielding efficiency (91%-100%), robust interfacial adhesion (lap-shear strength >3.8 MPa), prominent flexibility, lightweight, and outstanding breathability. The design concepts of fibrosing biphasic absorber assemblies pave the way for asymmetrically assembling biphasic materials, setting the stage for a fundamental shift in next-generation radiation shielding materials.

Large-scale assembly of isotropic nanofiber aerogels based on columnar-equiaxed crystal transition

Ice-templating technology holds great potential to construct industrial porous materials from nanometers to the macroscopic scale for tailoring thermal, electronic, or acoustic transport. Herein, we describe a general ice-templating technology through freezing the material on a rotating cryogenic drum surface, crushing it, and then re-casting the nanofiber slurry. Through decoupling the ice nucleation and growth processes, we achieved the columnar-equiaxed crystal transition in the freezing procedure. The highly random stacking and integrating of equiaxed ice crystals can organize nanofibers into thousands of repeating microscale units with a tortuous channel topology. Owing to the spatially well-defined isotropic structure, the obtained Al2O3·SiO2 nanofiber aerogels exhibit ultralow thermal conductivity, superelasticity, good damage tolerance, and fatigue resistance. These features, together with their natural stability up to 1200 °C, make them highly robust for thermal insulation under extreme thermomechanical environments. Cascading thermal runaway propagation in a high-capacity lithium-ion battery module consisting of LiNi0.8Co0.1Mn0.1O2 cathode, with ultrahigh thermal shock power of 215 kW, can be completely prevented by a thin nanofiber aerogel layer. These findings not only establish a general production route for nanomaterial assemblies that is conventionally challenging, but also demonstrate a high-energy-density battery module configuration with a high safety standard that is critical for practical applications.

Superelastic Cobalt Silicate@Resorcinol Formaldehyde Resin Core-Shell Nanobelt Aerogel Monoliths with Outstanding Fire Retardant and Thermal Insulating Capability

The practical applications of resorcinol formaldehyde resin (RFR) aerogels are prevented by their poor mechanical properties. Herein, a facile template-directed method is reported to produce macroscopic free-standing cobalt silicate (CS)@RFR core-shell nanobelt aerogels that display superelastic behavior and outstanding thermal insulating and fire-resistant capability. The synthesis relies on the polymerization of RFR on pre-formed CS nanobelts which leads to in situ formation of hydrogel monoliths that can be transformed to corresponding aerogels by a freeze-drying method. The composite nanobelt aerogel can withstand a compressive load of more than 4000 times of its own weight and fully recover after the removal of the weight. It can also sustain 1000 compressive cycles with 6.9% plastic deformation and 91.8% of the maximum stress remaining, with a constant energy loss coefficient as low as 0.16, at the set strain of 30%. The extraordinary mechanical properties are believed to be associated with the structural flexibility of the nanobelts and the RFR-reinforced joints between the crosslinked nanobelts. These inorganic-organic composite aerogels also show good thermal insulation and excellent fire-proof capability. This work provides an effective strategy for fabricating superelastic RFR-based aerogels which show promising applications in fields such as thermal insulation, energy storage, and catalyst support.

Aerogel-Based Biomaterials for Biomedical Applications: From Fabrication Methods to Disease-Targeting Applications

Aerogel-based biomaterials are increasingly being considered for biomedical applications due to their unique properties such as high porosity, hierarchical porous network, and large specific pore surface area. Depending on the pore size of the aerogel, biological effects such as cell adhesion, fluid absorption, oxygen permeability, and metabolite exchange can be altered. Based on the diverse potential of aerogels in biomedical applications, this paper provides a comprehensive review of fabrication processes including sol-gel, aging, drying, and self-assembly along with the materials that can be used to form aerogels. In addition to the technology utilizing aerogel itself, it also provides insight into the applicability of aerogel based on additive manufacturing technology. To this end, how microfluidic-based technologies and 3D printing can be combined with aerogel-based materials for biomedical applications is discussed. Furthermore, previously reported examples of aerogels for regenerative medicine and biomedical applications are thoroughly reviewed. A wide range of applications with aerogels including wound healing, drug delivery, tissue engineering, and diagnostics are demonstrated. Finally, the prospects for aerogel-based biomedical applications are presented. The understanding of the fabrication, modification, and applicability of aerogels through this study is expected to shed light on the biomedical utilization of aerogels.

Highly Efficient Thermo-acoustic Insulating Aerogels Enabled by Resonant Cavity Engineering

Lightweight, flexible, and noncombustible thermo-acoustic insulating (TAI) materials have great potential in vehicles, cold-chain transportation, and aerospace engineering, where weight and space savings are critical. However, the TAI capabilities of many commodities are hindered by the lack of diverse and reasonable resonant cavities with broadband and highly efficient acoustic responsiveness. This study demonstrates a layer-by-layer freeze-casting method for superelastic cellular aerogel construction from varied nanofibers and ice particulates with widely distributed resonant cavities from 0.5 to 300 μm. The method enabled the cumulative freezing of the nanofiber solution from one side to the other side, resulting in vertical pore channels with random holes across the entire freezing distance. The formed cellular networks of stable hinged ternary nanofiber membranes, functionalized as ultrathin nanofiber drums, exhibit strong resonances and efficiently dissipate sound waves in a broad frequency range. A high noise reduction coefficient of 0.65 at a frequency range of 63-6300 Hz and a low thermal conductivity of 0.026 W m^-1 K^-1 at room temperature was obtained. This work presents the bottom-up fabrication of high-performance TAI aerogels that are beneficial for practical energy-saving devices and buildings and broadband acoustic absorption applications.

Multifunctional Hierarchical Metamaterial for Thermal Insulation and Electromagnetic Interference Shielding at Elevated Temperatures

The custom design of lightweight cellular materials is widely concerned due to effectively improved mechanical properties and functional applications. However, the strength attenuation and brittleness behavior hinder honeycomb structure design for the ceramic monolith. Herein, the ceramic matrix composite metamaterial (CCM) with a negative Poisson's ratio and high specific strength, exhibiting superelasticity, stability, and high compressive strength, is customized by combining centripetal freeze-casting and hierarchical structures. CCM maintains a negative Poisson's ratio response under compression with the lowest value reaching -0.16, and the relationship between CCM's specific modulus and density is E ∼ ρ^1.3, which indicates the mechanical metamaterial characteristic of high specific strength. In addition to the extraordinary mechanical performance endowed by hierarchical structures, the CCM exhibits excellent thermal insulation and electromagnetic interference shielding properties, in which the thermal conductivity is 30.62 mW·m^-1·K^-1 and the electromagnetic interference (EMI) shielding efficiency (SE) reaches 40 dB at room temperature. The specific EMI shielding efficiency divided by thickness (SSE/t) of CCM can reach 9416 dB·cm²·g^-1 at 700 °C due to its stability at elevated temperatures, which is 100 times higher than that of traditional ceramic matrix composites. Moreover, the designed hierarchical structure and metamaterial properties provide a potential scheme to implement cellular materials with collaborative optimization in structure and function.

Multi-layered cement-hydrogel composite with high toughness, low thermal conductivity, and self-healing capability

The inherent quasi-brittleness of cement-based materials, due to the disorder of their hydration products and pore structures, present significant challenges for directional matrix toughening. In this work, a rigid layered skeleton of cement slurry was prepared using a simplified ice-template method, and subsequently flexible polyvinyl alcohol hydrogel was introduced into the unidirectional pores between neighboring cement platelets, resulting in the formation of a multi-layered cement-based composite. A toughness improvement of over 175 times is achieved by the implantation of such hard-soft alternatively layered microstructure. The toughening mechanism is the stretching of hydrogels at the nano-scale and deflections of micro-cracks at the interfaces, which avoid stress concentration and dissipate huge energy. Furthermore, this cement-hydrogel composite also exhibits a low thermal conductivity (around 1/10 of normal cement) and density, high specific strength and self-healing properties, which can be used in thermal insulation, seismic high-rise buildings and long-span bridges.

Ultralight elastic Al2O3 nanorod-graphene aerogel for pressure sensing and thermal superinsulation

Novel nanorod aerogels have gained tremendous attention owing to their unique structure. However, the intrinsic brittleness of ceramics still severely limits their further functionalization and application. Here, based on the self-assembly between one-dimensional (1D) Al₂O₃ nanorods and two-dimensional (2D) graphene sheets, lamellar binary Al₂O₃ nanorod-graphene aerogels (ANGAs) were prepared by the bidirectional freeze-drying technique. Thanks to the synergistic effect of rigid Al₂O₃ nanorods and high specific extinction coefficient elastic graphene, the ANGAs not only exhibit robust structure and variable resistance under pressure, but also possess superior thermal insulation properties compared to pure Al₂O₃ nanorod aerogels. Therefore, a series of fascinating features such as ultra-low density (3.13-8.26 mg cm^-3), enhanced compressive strength (6 times higher than graphene aerogel), excellent pressure sensing durability (500 cycles at 40% strain) and ultra-low thermal conductivity (0.0196 W m^-1 K^-1 at 25 °C and 0.0702 W m^-1 K^-1 at 1000 °C) are integrated in ANGAs. The present work provides fresh insight into the fabrication of ultralight thermal superinsulating aerogels and the functionalization of ceramic aerogels.

Highly Deformable High-Strength SiO2 Aerogel Designed with an Alternating Structure of Hard Cores and Flexible Chains for Thermal Insulation

Thermally insulating aerogels can now be prepared from ceramics, polymers, carbon, and metals and composites between them. However, it is still a great challenge to make aerogels with high strength and excellent deformability. We propose a design concept of hard cores and flexible chains that alternately construct the aerogel skeleton structure. The approach gives the designed SiO₂ aerogel excellent compressive (fracture strain 83.32%), tensile. and shear deformabilities, corresponding to maximum strengths of 22.15, 1.18, and 1.45 MPa, respectively. Also, the SiO₂ aerogel can stably perform 100 load-unload cycles at a 70% large compression strain, demonstrating an excellent resilient compressibility. In addition, the low density of 0.226 g/cm³, the high porosity of 88.7%, and the average pore size of 45.36 nm effectively inhibit heat conduction and heat convection, giving the SiO₂ aerogel outstanding thermal insulation properties [0.02845 W/(m·K) at 25 °C and 0.04895 W/(m·K) at 300 °C], and the large number of hydrophobic groups itself also gives it excellent hydrophobicity and hydrophobic stability (hydrophobic angle of 158.4° and saturated mass moisture absorption rate of about 0.327%). The successful practice of this concept has provided different insights into the preparation of high-strength aerogels with high deformability.

Bioinspired Aerogel with Vertically Ordered Channels and Low Water Evaporation Enthalpy for High-Efficiency Salt-Rejecting Solar Seawater Desalination and Wastewater Purification

Solar energy-driven water evaporation is a promising sustainable strategy to purify seawater and contaminated water. However, developing solar evaporators with high water evaporation rates and excellent salt resistance still faces a great challenge. Herein, inspired by the long-range ordered structure and water transportation capability of lotus stem, a biomimetic aerogel with vertically ordered channels and low water evaporation enthalpy for high-efficiency solar energy-driven salt-resistant seawater desalination and wastewater purification is developed. The biomimetic aerogel consists of ultralong hydroxyapatite nanowires as heat-insulating skeletons, polydopamine-modified MXene as a photothermal material with broadband sunlight absorption and high photothermal conversion efficiency, polyacrylamide, and polyvinyl alcohol as reagents to lower the water evaporation enthalpy and as glues to enhance the mechanical performance. The honeycomb porous structure, unidirectionally aligned microchannels, and nanowire/nanosheet/polymer pore wall endow the biomimetic aerogel with excellent mechanical properties, rapid water transportation, and excellent solar water evaporation performance. The biomimetic aerogel exhibits a high water evaporation rate (2.62 kg m^-2  h^-1 ) and energy efficiency (93.6%) under one sun irradiation. The superior salt-rejecting ability of the designed water evaporator enables stable and continuous seawater desalination, which is promising for application in water purification to mitigate the global water crisis.

Bioinspired Super Thermal Insulating, Strong and Low Carbon Cement Aerogel for Building Envelope

The energy crisis has arisen as the most pressing concern and top priority for policymakers, with buildings accounting for over 40% of global energy consumption. Currently, single-function envelopes cannot satisfy energy efficiency for next-generation buildings. Designing buildings with high mechanical robustness, thermal insulation properties, and more functionalities has attracted worldwide attention. Further optimization based on bioinspired design and material efficiency improvement has been adopted as effective approaches to achieve satisfactory performance. Herein, inspired by the strong and porous cuttlefish bone, a cement aerogel through self-assembly of calcium aluminum silicate hydrate nanoparticles (C-A-S-H, a major component in cement) in a polymeric solution as a building envelop is developed. The as-synthesized cement aerogel demonstrates ultrahigh mechanical performance in terms of stiffness (315.65 MPa) and toughness (14.68 MJ m^-3 ). Specifically, the highly porous microstructure with multiscale pores inside the cement aerogel greatly inhibits heat transfer, therefore achieving ultralow thermal conductivity (0.025 W m^-1 K^-1 ). Additionally, the inorganic C-A-S-H nanoparticles in cement aerogel form a barrier against fire for good fire retardancy (limit oxygen index, LOI ≈ 46.26%, UL94-V0). The versatile cement aerogel featuring high mechanical robustness, remarkable thermal insulation, light weight, and fire retardancy is a promising candidate for practical building applications.