Superhydrophobic Highly Flexible Triple-Network Polyorganosiloxane-Based Aerogels for Thermal Insulation, Oil-Water Separation, and Strain/Pressure Sensing

Polyvinylpolymethylsiloxane (PVPMS)/polydimethylsiloxane (PDMS) copolymer aerogels were synthesized via consecutive radical polymerization and cohydrolytic polycondensation of vinylmethyldimethoxysilane and dimethyldimethoxysilane, followed by supercritical drying or ambient pressure drying. The resultant PVPMS/PDMS copolymer aerogels exhibit a highly porous, tunable triple-network structure consisting of interlinked hydrocarbon polymers, PVPMS and PDMS. These aerogels display superhydrophobicity (151°), low density (109 mg cm-3), low thermal conductivity (29.8 mW m-1 K-1), and adjustable pore structure. The combination of good machinability, low thermal conductivity, excellent compressive elasticity and bending flexibility, and efficient organic solvent adsorption gives these aerogels broad application prospects in thermal insulation and oil-water separation. In addition, PVPMS/PDMS/carbon nanotube (CNT) composite aerogels were obtained by incorporating the conductive CNTs, followed by vacuum drying. The resultant PVPMS/PDMS/CNT composite aerogel exhibits high sensitivity with a broad pressure sensing range in strain and pressure sensing applications.

Biomimetic Transparent Layered Tough Aerogels for Thermal Superinsulation and Triboelectric Nanogenerator

Transparent aerogels are ideal candidates for thermally insulating windows, solar thermal receivers, electronics, etc. However, they are usually prepared via energy-consuming supercritical drying and show brittleness and low tensile strength, significantly restricting their practical applications. It remains a great challenge to prepare transparent aerogels with high tensile strength and toughness. Herein, biomimetic transparent tough cellulose nanofiber-based nanocomposite aerogels with a layered nanofibrous structure are achieved by vacuum-assisted self-assembly combined with ambient pressure drying. The nacre-like layered homogeneous nanoporous structures can reduce light scattering and effectively transfer stress and prevent stress concentration under external forces. The aerogels exhibit an attractive combination of excellent transparency and hydrophobicity, high compressive and tensile strengths, high toughness, excellent machinability, thermal superinsulation, and wide working temperature range (-196 to 230 °C). It is demonstrated that they can be used for superinsulating windows of buildings and high-efficient thermal management for electronics and human bodies. In addition, a prototype of transparent flexible aerogel-based triboelectric nanogenerator is developed. This work provides a promising pathway toward transparent tough porous materials for energy saving/harvesting, thermal management, electronics, sensors, etc.

Flexible Aerogel Materials: A Review on Revolutionary Flexibility Strategies and the Multifunctional Applications

The design and preparation of flexible aerogel materials with high deformability and versatility have become an emerging research topic in the aerogel fields, as the brittle nature of traditional aerogels severely affects their safety and reliability in use. Herein, we review the preparation methods and properties of flexible aerogels and summarize the various controlling and design methods of aerogels to overcome the fragility caused by high porosity and nanoporous network structure. The mechanical flexibility of aerogels can be revolutionarily improved by monomer regulation, nanofiber assembly, structural design and controlling, and constructing of aerogel composites, which can greatly broaden the multifunctionality and practical application prospects. The design and construction criterion of aerogel flexibility is summarized: constructing a flexible and deformable microstructure in an aerogel matrix. Besides, the derived multifunctional applications in the fields of flexible thermal insulation (flexible thermal protection at extreme temperatures), flexible wearable electronics (flexible sensors, flexible electrodes, electromagnetic shielding, and wave absorption), and environmental protection (oil/water separation and air filtration) are summarized. Furthermore, the future development prospects and challenges of flexible aerogel materials are also summarized. This review will provide a comprehensive research basis and guidance for the structural design, fabrication methods, and potential applications of flexible aerogels.

Polyphosphonate-segmented macroporous organosilicon frameworks for efficient dynamic enrichment of uranium with in-situ regeneration

Efficient separation and enrichment of uranium from radioactive effluents is of strategic significance for sustainable development of nuclear energy and environmental protection. Macropore structure of adsorbent is conducive to accessibility of the pore and transport of the adsorbate during dynamic adsorption. However, the low specific surface area results in fewer ligand sites and subsequently reduces the adsorption capacity. Herein, we present a novel strategy for efficient dynamic uranium enrichment using polyphosphonate-segmented macroporous organosilicon frameworks (PMOFs). PMOFs are constructed through the copolymerization of diethyl vinylphosphonate and triethoxyvinylsilane, followed by hydrolysis and condensation of the oligomers. The introduction of polyphosphonate segments into the frameworks endows PMOFs with a macroporous structure (31 µm) and a high ligand content (up to 72 wt%). Consequently, the optimized PMOF-3 demonstrated an ultrahigh dynamic adsorption capacity of 114.8 mg/g among covalently conjugated silicon-based materials. Additionally, PMOF-3 achieves a high enrichment factor (120) in the dynamic enrichment of uranium on a fixed bed column, which can be in-situ regenerated with 1 M NaHCO₃ as the eluent. This work presents a new strategy for efficient dynamic enrichment of nuclides, which can be extended to the separation of other specific pollutants, shedding new light on adsorbent design and technical innovation.

Ultralight Biomass Aerogels with Multifunctionality and Superelasticity Under Extreme Conditions

Biomass aerogels are highly attractive candidates in various applications due to their intrinsic merits of high strength, high porosity, biodegradability, and renewability. However, under low-temperature harsh conditions, biomass aerogels suffer from weakened mechanical properties, become extremely brittle, and lose functionality. Herein, we report a multifunctional biomass aerogel with lamella nanostructures (∼1 μm) fabricated from cellulose nanofibers (∼200 nm) and gelatin, showing outstanding elasticity from room temperature to ultralow temperatures (repeatedly bent, twisted, or compressed in liquid nitrogen). The resultant aerogel exhibits excellent organic solvent absorption, thermal infrared stealth, and thermal insulation performance in both normal and extreme environments. Even at dry ice temperature (-78 °C), the aerogel can selectively and repeatedly absorb organic solvents in the same way as room temperature with high capacities (90-177 g/g). Excellent heat insulation and infrared stealth performances are achieved in a wide temperature range of -196 to 80 °C. Further, this aerogel combines with the advantages of ultralow density (∼6 mg/cm³), biodegradability, flame retardancy, and performance stability, making it a perfect candidate for multifunctional applications under harsh conditions. This work greatly broadens application temperature windows of biomass aerogels and sheds light on the development of mechanically robust biomass aerogels for various applications under extreme conditions.

Nacre-Mimetic, Mechanically Flexible, and Electrically Conductive Silk Fibroin-MXene Composite Foams as Piezoresistive Pressure Sensors

The hierarchical nacre-like three-dimensional (3D) assembly of porous and lightweight materials is in high demand for applications such as sensors, flexible energy storage and harvesting devices, electromagnetic interference shielding, and biomedical applications. However, designing such a biomimetic hierarchical architecture is highly challenging due to the lack of experimental approaches to achieve the necessary control over the materials' microstructure on the multilength scale. Aerogels and foam-based materials have recently been developed as attractive candidates for pressure-sensing applications. However, despite recent progress, the bottleneck for these materials to achieve electrical conductivity combined with high mechanical flexibility and fast strain recovery remains. In this study, for the first time, inspired by the multiscale architecture of nacre, we fabricated a series of ultra-lightweight, flexible, electrically conductive, and relatively high-strength composite foams through hybridizing the cross-linked silk fibroin (SF) biopolymer, extracted from Bombyx mori silkworm cocoon, reinforced with two-dimensional graphene oxide (GO) and Ti₃C₂ MXene nanosheets. Nacre is a naturally porous material with a lightweight, mechanically robust network structure, thanks to its 3D interconnected lamella-bridge micromorphology. Inspired by this material, we assemble a cross-linked SF fibrous solution with MXene and GO nanosheets into nacre-like architecture using a bidirectional freeze-casting technique. Subsequent freeze-drying and gas-phase hydrophobization resulted in composite foams with 3D hierarchical porous architectures with a unique combination of mechanical resilience, electrical conductance, and ultra-lightness. The developed composite presented excellent performances as piezoresistive pressure-sensing devices and sorbents for oil/water separation, which indicated great potential in mechanically switchable electronics.

Recent Developments in Nanocellulose-Based Aerogels in Thermal Applications: A Review

Naturally derived nanocellulose (NC) is a renewable, biodegradable nanomaterial with high strength, low density, high surface area, and tunable surface chemistry, which allows its interaction with other polymers and nanomaterials in a controlled manner. In recent years, NC aerogel has gathered a lot of attention due to environmental concerns. This review presents recent developments of NC-based aerogels and their controlled interactions with other polymers and nanomaterials for thermal applications that include electronic devices, the apparel industry, superinsulating materials, and flame-retardant smart building materials. After going through the distinctive properties of NC aerogels, they are orderly categorized and discussed as thermally insulated, thermally conductive, and flame-retardant materials.

Polymeric hybrid aerogels and their biomedical applications

Aerogels are a class of porous materials that possess extremely high specific surface area, high pore volume, high porosity, and variable chemical structures. They have been widely applied in the fields of aerospace, chemical engineering, construction, electrotechnics, and biomedicine. In recent years a great boom in aerogels has been observed, where various new aerogels with novel physicochemical properties and functions have been synthesized. Nevertheless, native aerogels with a single component normally face severe problems such as low mechanical strength and lack of functions. One strategy to solve the problems is to construct hybrid aerogels. In this study, a comprehensive review on polymer based hybrid aerogels is presented, including polymer-polymer, polymer-carbon material, and polymer-inorganic hybrid aerogels, which will be introduced and discussed in view of their chemical structures and hybrid structures. Most importantly, polymeric hybrid aerogels are classified into three different composition levels, which are molecular-level, molecular-aggregate-level, and aggregate-level, due to the fact that hybrid aerogels with the same chemical structures but with different composition levels might show quite different functions or properties. The biomedical applications of these hybrid aerogels will also be reviewed and discussed, where the polymeric components in the hybrid aerogels provide the main contribution. This review would provide creative design principles for aerogels by considering both their chemical and physical structures.

Extending the pressure sensing range of porous polypyrrole with multiscale microstructures

Polymer-based piezoresistive sensors that combine the flexibility and stretchability of organic polymers have received considerable attention in flexible and wearable sensing systems. Generally, highly sensitive pressure sensors have a limited pressure sensing range, while pressure sensors with a wide pressure response range usually have limited pressure resolution. Herein, we used a polypyrrole (PPy) sponge with multiscale porous structures to extend the pressure sensing range of PPy-based piezoresistive sensors. The multiscale microstructures with different sizes will sink in sequence after increasing the external pressure and therefore exhibit a wide pressure response range. Our results show that the piezoresistive composite has a superior sensitivity of 28 kPa-1 and a broad stress range of 0-60 kPa. Moreover, the composite displays a stable, repeatable and durable performance over 16 000 cycles. It can be used to monitor diverse body part motions, including vocalization, pulse beating and joint bending. This work provides an effective strategy to extend the pressure sensing range of polymer-based piezoresistive sensors in the manner of structure design rather than modifying the intrinsic properties of active materials.