Silica aerogels have incomparable advantages among thermal insulation materials because of their ultralow density and thermal conductivity, but cumbersome production processes, high cost, and low mechanical stability limit their practical application. In this study, a novel aqueous process to prepare lightweight aerogel-like silica foams (ASFoams) through the cast-in situ method and ambient pressure drying was proposed with multiblock polyurethane surfactant as the vesicle template. ASFoams possess a unique loose stacking morphology of the silica hollow sphere with a 3D network structure as the skeleton, which endues ASFoams with a low density of 0.059 g/cm, low thermal conductivity of 36.1 mW·k·m, and pretty good mechanical properties. These properties make ASFoams a promising option for thermal insulation in industrial, aerospace, and other extreme environmental conditions. In addition, the micromorphology of ASFoams can be adjusted by changing the reaction conditions, which may provide a facile method for the preparation of a silica aerogel-like foam with adjustable microstructure.

Lightweight, robust, and thin aerogel films with multifunctionality are highly desirable to meet the technological demands of current society. However, fabrication and application of these multifunctional aerogel films are still significantly underdeveloped. Herein, we demonstrate a multifunctional aerogel film composed of strong aramid nanofibers (ANFs), conductive carbon nanotubes (CNTs), and hydrophobic fluorocarbon (FC) resin. The obtained hybrid aerogel film exhibits large specific surface area (232.8 m·g), high electrical conductivity (230 S·m), and excellent hydrophobicity (contact angle of up to 137.0°) with exceptional Joule heating performance and supreme electromagnetic interference (EMI) shielding efficiency. The FC coating renders the hydrophilic ANF/CNT aerogel films hydrophobic, resulting in an excellent self-cleaning performance. The high electrical conductivity enables a low-voltage-driven Joule heating property and an EMI shielding effectiveness (SE) of 54.4 dB in the X-band at a thickness of 568 μm. The specific EMI SE is up to 33528.3 dB·cm·g, which is among the highest values of typical metal-, conducting-polymer-, or carbon-based composites. This multifunctional aerogel film holds great promise for smart garments, electromagnetic wave shielding, and personal thermal management systems.

Stable dispersions of nanofibers are virtually unknown for synthetic polymers. They can complement analogous dispersions of inorganic components, such as nanoparticles, nanowires, nanosheets, etc. as a fundamental component of a toolset for design of nanostructures and metamaterials via numerous solvent-based processing methods. As such, strong flexible polymeric nanofibers are very desirable for the effective utilization within composites of nanoscale inorganic components such as nanowires, carbon nanotubes, graphene, and others. Here stable dispersions of uniform high-aspect-ratio aramid nanofibers (ANFs) with diameters between 3 and 30 nm and up to 10 μm in length were successfully obtained. Unlike the traditional approaches based on polymerization of monomers, they are made by controlled dissolution of standard macroscale form of the aramid polymer, that is, well-known Kevlar threads, and revealed distinct morphological features similar to carbon nanotubes. ANFs are successfully processed into films using layer-by-layer (LBL) assembly as one of the potential methods of preparation of composites from ANFs. The resultant films are transparent and highly temperature resilient. They also display enhanced mechanical characteristics making ANF films highly desirable as protective coatings, ultrastrong membranes, as well as building blocks of other high performance materials in place of or in combination with carbon nanotubes.© 2011 American Chemical Society

Aramid nanofibers (ANFs) have become promising nanoscale building blocks due to their extraordinary performance. However, there are numerous challenges related to the preparation of ANFs, such as the lengthy preparation cycle (7-10 days), low preparation concentration (0.2 wt %), and high difficulty in quantitatively judging the end point of the deprotonation reaction. Herein, we report three time-saving and high-efficiency strategies (fibrillation, ultrasonication, and proton donor-assisted deprotonation) to prepare ANFs with excellent performance. The fiber micromorphology during the deprotonation and protonation recovery processes was first investigated. Then the end point of the deprotonation reaction was detected by Raman spectra and the cationic demand of the ANF/DMSO system. Finally, the size, preparation cycle, and performance of the corresponding ANFs and ANF films fabricated by different approaches were investigated in detail. The results showed that proton donor-assisted deprotonation significantly shortened the traditional preparation cycle from 7 days to 4 h, and is the most efficient method reported thus far. It is noteworthy that a high concentration of ANFs (4.0 wt %) could also be achieved within 12 h. Interestingly, the fabricated ANFs exhibit rigid morphology and a small diameter with a narrow size distribution (10.7 ± 1.0 nm). The resultant ANF film displays desired characteristics of high strength and toughness. The work offers a timesaving, feasible and effective strategy to realize the large-scale production for ANFs, which will facilitate the application of ANFs in the production of advanced nanomaterials.

Electrospinning is a highly versatile method to process solutions or melts, mainly of polymers, into continuous fibers with diameters ranging from a few micrometers to a few nanometers. This technique is applicable to virtually every soluble or fusible polymer. The polymers can be chemically modified and can also be tailored with additives ranging from simple carbon-black particles to complex species such as enzymes, viruses, and bacteria. Electrospinning appears to be straightforward, but is a rather intricate process that depends on a multitude of molecular, process, and technical parameters. The method provides access to entirely new materials, which may have complex chemical structures. Electrospinning is not only a focus of intense academic investigation; the technique is already being applied in many technological areas.

Aerogel fibers, the simultaneous embodiment of aerogel porous network and fiber slender geometry, have shown critical advantages over natural and synthetic fibers in thermal insulation. However, how to control the building block orientation degree of the resulting aerogel fibers during the dynamic sol-gel transition process to expand their functions for emerging applications is a great challenge. Herein, nanoscale Kevlar liquid crystal (NKLC) aerogel fibers with different building block orientation degrees have been fabricated from Kevlar nanofibers liquid crystal spinning, dynamic sol-gel transition, freeze-drying, and cold plasma hydrophobilization in sequence. The resulting NKLC aerogel fibers demonstrate extremely high mechanical strength (41.0 MPa), excellent thermal insulation (0.037 W·m·K), and self-cleaning performance (with a water contact angle of 154°). The superhydrophobic NKLC aerogel fibers can cyclically transform between aerogel and gel states, while gel fibers involving different building block orientation degrees display distinguishable brightness under polarized light. Based on these performances, digital textiles woven or embroidered with high- and low-orientated NKLC aerogel fibers enable up to 6.0 Gb information encryption in one square meter and on-demand decryption. Therefore, it can be envisioned that the tuning of the building blocks' orientation degree will be an appropriate strategy to endow performance to the liquid crystal aerogel fibers for potential applications beyond thermal insulation.

Aerogel with low density, high porosity, and large surface area is a promising structure for the next generation of high-performance thermal insulation fibers and textiles. However, aerogel fibers suffer from weak mechanical properties or complex fabricating processes. Herein, a facile wet-spinning approach for fabricating nanofibrous Kevlar (KNF) aerogel threads ( i.e., aerogel fibers) with high thermal insulation under extreme environments is demonstrated. The aerogel fibers made from nanofibrous Kevlar render a high specific surface area (240 m/g) and wide-temperature thermal stability. The flexible and strong KNF aerogel fibers are woven into textiles to illustrate the excellent thermal insulation property under extreme temperature (-196 or +300 °C) and at room temperature. COMSOL simulation is applied to calculate the thermal conductivity of a single aerogel fiber and find an effective way to improve the thermal insulation property of the aerogel fiber. Furthermore, a series of functionalized fibers or textiles based on KNF aerogel fibers, such as phase-change fibers, conductive fibers, and hydrophobic textiles, have been prepared. Such KNF aerogel fibers represent a promising direction for the next generation of high-performance fibrous thermal-insulation materials.

Smart and functional fibers have demonstrated great potentials in a wide range of applications including wearable devices and other high-tech fields, but design and fabrication of smart fibers with manageable structures as well as versatile functions are still a great challenge. Herein, an ingenious bending-stiffness-directed strategy is developed to fabricate smart phase-change fibers with different bending stiffnesses for diverse applications. Specifically, the hydrophobic Kevlar aerogel-confined paraffin wax fibers (PW@H-KAF) are fabricated by employing hydrophobic Kevlar aerogel fibers (H-KAFs) as the porous host and paraffin as the functional guest, where the H-KAF is obtained by applying a two-step process to functionalize Kevlar nanofibers (KNFs) with a special coagulation bath containing a mixture of ethanol and -bromobutane. The prepared PW@H-KAFs exhibit high latent heat (135.1-172 J/g), outstanding thermal cyclic stability and satisfactory mechanical properties (30 MPa in tensile strength and 30% in tensile strain). In addition, the PW@H-KAFs with bending stiffness was lower than the critical one (1.22 × 10 N·m) even in a solid state of paraffin wax exhibits high flexibility, washable performance, and high thermal management capability, showing great potential for smart temperature-regulating fabrics. PW@H-KAFs with a bending stiffness higher than the critical one at a solid state of paraffin wax can be utilized as shape memory materials, attributed to the transition between rigidity and flexibility caused by the phase transition. As a proof of concept, a dynamic gripper is designed based on the PW@H-KAF (400 μm in diameter) for transporting items by gripping in the rigid state and releasing in the flexible state. This work realizes versatile applications with the PW@H-KAFs through the bending stiffness-directed method, providing ideas for the application of phase-change composites.

Aerogel has been much highlighted as an emerging lightweight thermal insulation material, but problems such as fragility, low strength, liquid permeability, and lack of flexibility greatly limit further applications. In this work, a facile aramid-coating-on-aramid (ACoA) method is demonstrated to fabricate all-aramid aerogel composite films for thermal insulation. The method started from the bottom-up synthesis of polymerization-induced -aramid nanofibers (PANF), which were easily transformed into aerogel films through the vacuum-assisted filtration followed by the freeze-drying techniques. Then, the heterocyclic aramid (HA) solution prepared through the low-temperature-solution polycondensation was used as the coating to be applied onto the PANF aerogel films, and composite films of HA/PANF aerogel were simply achieved with HA contributed to the dense and continuous surface layer. The bulk HA film is of superior mechanical and thermal properties to those of the PANF film. Moreover, reliable interfacial interlocking structures were developed beneath the outermost surface via the interpenetration of the infiltrated HA with PANF network. The comprehensive result was the 15 times enhanced tensile strength, 33 times enhanced fracture toughness, the high thermal decomposition temperature, and the additional flexibility for the foldable films of HA/PANF aerogel. The sealing of the surface macropores greatly suppressed the surface chalking and high water absorption. However, the survival of the tiny pores inside the composite maintained the low enough level of the thermal conductivity to provide effective protections against high temperature not only in air but also under wet or even liquid conditions, suggesting the broader applications for thermal insulation.

Infrared (IR) stealth is essential not only in high technology and modern military but also in fundamental material science. However, effectively hiding targets and rendering them invisible to thermal infrared detectors have been great challenges in past decades. Herein, flexible, foldable, and robust Kevlar nanofiber aerogel (KNA) films with high porosity and specific surface area were fabricated first. The KNA films display excellent thermal insulation performance and can be employed to incorporate with phase-change materials (PCMs), such as polyethylene glycol, to fabricate KNA/PCM composite films. The KNA/PCM films with high thermal management capability and infrared emissivity comparable to that of various backgrounds demonstrate high performance in IR stealth in outdoor environments with solar illumination variations. To further realize hiding hot targets from IR detection, combined structures constituted of thermal insulation layers (KNA films) and ultralow IR transmittance layers (KNA/PCM) are proposed. A hot target covered with this combined structure becomes completely invisible in infrared images. Such KNA/PCM films and KNA-KNA/PCM combined structures hold great promise for broad applications in infrared thermal stealth.

High-throughput fabrication techniques for generating arbitrarily complex three-dimensional structures with nanoscale features are desirable across a broad range of applications. Two-photon lithography (TPL)-based submicrometer additive manufacturing is a promising candidate to fill this gap. However, the serial point-by-point writing scheme of TPL is too slow for many applications. Attempts at parallelization either do not have submicrometer resolution or cannot pattern complex structures. We overcome these difficulties by spatially and temporally focusing an ultrafast laser to implement a projection-based layer-by-layer parallelization. This increases the throughput up to three orders of magnitude and expands the geometric design space. We demonstrate this by printing, within single-digit millisecond time scales, nanowires with widths smaller than 175 nanometers over an area one million times larger than the cross-sectional area.Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Graphene-based mixed-dimensional materials hybridization is important for a myriad of applications. However, conventional manufacturing techniques face critical challenges in producing arbitrary geometries with programmable features, continuous interior networks, and multimaterials homogeneity. Here we propose a generalized three-dimensional (3D) printing methodology for graphene aerogels and graphene-based mixed-dimensional (2D + nD, where n is 0, 1, or 2) hybrid aerogels with complex architectures, by the development of hybrid inks and printing schemes to enable mix-dimensional hybrids printability, overcoming the limitations of multicomponents inhomogeneity and harsh post-treatments for additives removal. Importantly, nonplanar designed geometries are also demonstrated by shape-conformable printing on curved surfaces. We further demonstrate the 3D-printed hybrid aerogels as ultrathick electrodes in a symmetric compression tolerant microsupercapacitor, exhibiting quasi-proportionally enhanced areal capacitances at high levels of mass loading. The excellent performance is attributed to the sufficient ion- and electron-transport paths provided by the 3D-printed highly interconnected networks. The encouraging finding indicates tremendous potentials for practical energy storage applications. As a proof of concept, this general strategy provides avenues for various next-generation complex-shaped hybrid architectures from microscale to macroscale, for example, seawater desalination devices, electromagnetic shielding systems, and so forth.

Aerogels represent a kind of nanoporous solid with immense importance for a plethora of diverse applications. However, on-demand conformal shaping capacity remains extremely challenging due to the strength unfavorable during aerogel processing. Herein, a universal microgel-directed suspended printing (MSP) strategy is developed for fabricating various mesoporous aerogels with spatially stereoscopic structures on-demand. As a proof-of-concept demonstration, through the rational design of the used microgel matrix and favorable printing of the Kevlar nanofiber inks, the Kevlar aerogels with arbitrary spatial structure have been fabricated, demonstrating excellent printability and programmability under a high-speed printing mode (up to 167 mm s). Furthermore, the custom-tailored Kevlar aerogel insulator possessing superior thermal insulation attribute has ensured normal discharge capacity of the drone even under a harsh environment (-30 °C). Finally, various types of spatial 3D aerogel architectures, including organic (cellulose, alginate, chitosan), inorganic (graphene, MXene, silica), and inorganic-organic (graphene/cellulose, MXene/alginate, silica/chitosan) hybrid aerogels, have been successfully fabricated, suggesting the universality of the MSP strategy. The strategy reported here proposes an alternative for the development of various customized aerogels and stimulates the inspiration to truly arbitrary architectures for wider applications.