Proton Donor-Regulated Mechanically Robust Aramid Nanofiber Aerogel Membranes for High-Temperature Thermal Insulation

Biomimetic Aramid Nanofiber/β-FeOOH Composite Coating for Polypropylene Separators in Lithium-Sulfur Batteries

Aramid nanofibers (ANFs), with attractive mechanical and thermal properties, have attracted much attention as key building units for the design of high-performance composite materials. Although great progress has been made, the potential of ANFs as fibrous protein mimetics for controlling the growth of inorganic materials has not been fully revealed, which is critical for avoiding phase separation associated with typical solution blending. In this work, we show that ANFs could template the oriented growth of β-FeOOH nanowhiskers, which enables the synthesis of ANFs/β-FeOOH hybrids as composite coatings for polypropylene (PP) separators in Li-S batteries. The modified PP separator exhibits enhanced mechanical properties, heightened thermal performance, optimized electrolyte wettability, and improved ion conductivity, leading to superior electrochemical properties, including high initial specific capacity, better rate capability, and long cycling stability, which are superior to those of the commercial PP separators. Importantly, the addition of β-FeOOH to ANFs could further contribute to the suppression of lithium polysulfide shuttling by chemical immobilization, inhibition of the growth of lithium dendrites because of the intrinsic high modulus and hardness, and promotion of reaction dynamics due to the catalytic effect. We believe that our work may provide a potent biomimetic pathway for the development of advanced battery separators based on ANFs.

Interpenetrated Multinetwork Hybrid Aerogels by Layered Montmorillonite and One-Dimensional Hydroxyapatite Fibers for Heat and Fire Insulation

It is of practical significance to develop aerogels with effective thermal insulation characteristics together with fireproof properties as well as high mechanical strength. Here, an interpenetrated multinetwork hybrid aerogel realizing thermal insulation, flame retardancy, and high compression modulus is demonstrated. Specifically, one-dimensional hydroxyapatite nanowires (HAP) played dual roles as the aerogel support skeleton to entangle with layered montmorillonite (MMT) each other to form a three-dimensional interpenetrated multinetwork structure and to optimize the thermal conductivity by adjusting the pore space in current HAP/MMT/PVA hybrid aerogels. Therefore, the interpenetrated multinetwork hybrid aerogels exhibit superior thermal insulation performance in room temperature (0.033 W m-1 K-1, 298 K, air conditions) and largely enhanced ultrahigh compression modulus (80 MPa). Moreover, the obtained hybrid aerogels also exhibit excellent flame retardancy and self-extinguishing smoke suppression properties (peak heat release rate and total smoke production as low as 92.44 kW m-2 and 0.1 m2, respectively), which is the outstanding interpenetrated multinetwork hybrid aerogel that has achieved synergistic improvement in heat and fire insulation and mechanical performance. Therefore, the interpenetrated multinetwork hybrid aerogels are promising candidates for efficient heat insulation, fire prevention, and mechanically robust applications.

The Synergistic Effect of Aramid Nanofibers and Carbon Nanotubes on Micro-Silicon Anodes for Improved Stability and Conductivity

Despite the continuous development of energy storage, the challenges faced by micro-silicon anode pulverization have yet to be effectively addressed. In this work, the aramid nanofibers (ANFs) are in situ protonated on the surface of silicon micro-particles (SMPs), and also act as surfactants to bundle the carbon nanotubes (CNTs) to form ANF/CNT networks on SMPs (ANF/CNT/SMPs) at the same time. The results demonstrate that the dual-coating not only inhibits expansion and enhances structural stability but also improves conductivity, thereby promoting the cycling stability of micro-silicon anodes. The ANF/CNT/SMP anode shows cycling stability of 454 mAh g-1 at 0.2 A g-1 after 200 cycles. The expansion in thickness of the ANF/CNT/SMP electrode can be reduced by 51.5% after 100 cycles compared with the SMP electrode. The findings provide a novel approach for mitigating expansion in micro-silicon anodes through the combined coating of ANFs and CNTs.

Controlled Structural Relaxation of Aramid Nanofibers for Superstretchable Polymer Fibers with High Toughness and Heat Resistance

Polymer fibers that combine high toughness and heat resistance are hard to achieve, which, however, hold tremendous promise in demanding applications such as aerospace and military. This prohibitive design task exists due to the opposing property dependencies on chain dynamics because traditional heat-resistant materials with rigid molecular structures typically lack the mechanism of energy dissipation. Aramid nanofibers have received great attention as high-performance nanoscale building units due to their intriguing mechanical and thermal properties, but their distinct structural features are yet to be fully captured. We show that aramid nanofibers form nanoscale crimps during the removal of water, which primarily resides at the defect planes of pleated sheets, where the folding can occur. The precise control of such a structural relaxation can be realized by exerting axial loadings on hydrogel fibers, which allows the emergence of aramid fibers with varying angles of crimps. These crimped fibers integrate high toughness with heat resistance, thanks to the extensible nature of nanoscale crimps with rigid molecular structures of poly(p-phenylene terephthalamide), promising as a template for stable stretchable electronics. The tensile strength/modulus (392-944 MPa/11-29 GPa), stretchability (25-163%), and toughness (154-445 MJ/cm3) are achieved according to the degree of crimping. Intriguingly, a toughness of around 430 MJ/m3 can be maintained after calcination below the relaxation temperature (259 °C) for 50 h. Even after calcination at 300 °C for 10 h, a toughness of 310 MJ/m3 is kept, outperforming existing polymer materials. Our multiscale design strategy based on water-bearing aramid nanofibers provides a potent pathway for tackling the challenge for achieving conflicting property combinations.

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.

Revealing Surface/Interface Chemistry of the Ordered Aramid Nanofiber/MXene Structure for Infrared Thermal Camouflage and Electromagnetic Interference Shielding

The past decade has witnessed the advances of infrared (IR) thermal camouflage materials, but challenges remain in breaking the trade-off nature between emissivity and mechanical properties. In response, we identify the key role of a moderate reprotonation rate in the aramid nanofiber (ANF)/MXene film toward a surface-to-bulk alignment. Theoretical simulation demonstrates that the ordered ANF/MXene surface eliminates the local high electric field by field confinement and localization, responsible for the low IR emissivity. By scrutinizing the surface/interface chemistry, the processing optimization is achieved to develop an ordered and densely stacked ANF/MXene film, which features a low emissivity of 16%, accounting for sound IR thermal camouflage performances including a wide camouflage temperature range of 50-200 °C, a large reduction in radiation temperature from 200.5 to 63.6 °C, and long-term stability. This design also enables good mechanical performance such as a tensile strength of 190.8 MPa, a toughness of 12.1 MJ m-3, and a modulus of 7.9 GPa, responsible for better thermal camouflage applications. The tailor-made ANF/MXene film further attains an electromagnetic interference (EMI) shielding effectiveness (40.4 dB) in the X-band, manifesting its promise for IR stealth compatible EMI shielding applications. This work will shed light on the dynamic topology reconstruction of camouflage materials for boosting thermal management technology.

Self-Assembly of Ultrathin, Ultrastrong Layered Membranes by Protic Solvent Penetration

Flexible membranes with ultrathin thickness and excellent mechanical properties have shown great potential for broad uses in solid polymer electrolytes (SPEs), on-skin electronics, etc. However, an ultrathin membrane (<5 μm) is rarely reported in the above applications due to the inherent trade-off between thickness and antifailure ability. We discover a protic solvent penetration strategy to prepare ultrathin, ultrastrong layered films through a continuous interweaving of aramid nanofibers (ANFs) with the assistance of simultaneous protonation and penetration of a protic solvent. The thickness of a pure ANF film can be controlled below 5 μm, with a tensile strength of 556.6 MPa, allowing us to produce the thinnest SPE (3.4 μm). The resultant SPEs enable Li-S batteries to cycle over a thousand times at a high rate of 1C due to the small ionic impedance conferred by the ultrathin characteristic and regulated ionic transportation. Besides, a high loading of the sulfur cathode (4 mg cm-2) with good sulfur utilization was achieved at a mild temperature (35 °C), which is difficult to realize in previously reported solid-state Li-S batteries. Through a simple laminating process at the wet state, the thicker film (tens of micrometers) obtained exhibits mechanical properties comparable to those of thin films and possesses the capability to withstand high-velocity projectile impacts, indicating that our technique features a high degree of thickness controllability. We believe that it can serve as a valuable tool to assemble nanomaterials into ultrathin, ultrastrong membranes for various applications.

Large-Scale Fabrication of Tunable Sandwich-Structured Silver Nanowires and Aramid Nanofiber Films for Exceptional Electromagnetic Interference (EMI) Shielding

The recent advancements in communication technology have facilitated the widespread deployment of electronic communication equipment globally, resulting in the pervasive presence of electromagnetic pollution. Consequently, there is an urgent necessity to develop a thin, lightweight, efficient, and durable electromagnetic interference (EMI) shielding material capable of withstanding severe environmental conditions. In this paper, we propose an innovative and scalable method for preparing EMI shielding films with a tunable sandwich structure. The film possesses a nylon mesh (NM) backbone, with AgNWs serving as the shielding coating and aramid nanofibers (ANFs) acting as the cladding layer. The prepared film was thin and flexible, with a thickness of only 0.13 mm. AgNWs can easily form a conductive network structure, and when the minimum addition amount was 0.2 mg/cm2, the EMI SE value reached 28.7 dB, effectively shielding 99.884% of electromagnetic waves and thereby meeting the commercial shielding requirement of 20 dB. With an increase in dosage up to 1.0 mg/cm2, the EMI SE value further improved to reach 50.6 dB. The NAAANF film demonstrated remarkable robustness in the face of complex usage environments as a result of the outstanding thermal, acid, and alkali resistance properties of aramid fibers. Such a thin, efficient, and environmentally resistant EMI shielding film provided new ideas for the broad EMI shielding market.

Thermally Insulating and Moisture-Resilient Foams Based on Upcycled Aramid Nanofibers and Nanocellulose

Low-density foams and aerogels based on upcycled and bio-based nanofibers and additives are promising alternatives to fossil-based thermal insulation materials. Super-insulating foams are prepared from upcycled acid-treated aramid nanofibers (upANFA ) obtained from Kevlar yarn and tempo-oxidized cellulose nanofibers (CNF) from wood. The ice-templated hybrid upANFA /CNF-based foams with an upANFA content of up to 40 wt% display high thermal stability and a very low thermal conductivity of 18-23 mW m-1 K-1 perpendicular to the aligned nanofibrils over a wide relative humidity (RH) range of 20% to 80%. The thermal conductivity of the hybrid upANFA /CNF foams is found to decrease with increasing upANFA content (5-20 wt%). The super-insulating properties of the CNF-upANFA hybrid foams are related to the low density of the foams and the strong interfacial phonon scattering between the very thin and partially branched upANFA and CNF in the hybrid foam walls. Defibrillated nanofibers from textiles are not limited to Kevlar, and this study can hopefully inspire efforts to upcycle textile waste into high-performance products.

Temperature-Arousing Self-Powered Fire Warning E-Textile Based on p-n Segment Coaxial Aerogel Fibers for Active Fire Protection in Firefighting Clothing

Firefighting protective clothing is a crucial protective equipment for firefighters to minimize skin burn and ensure safety firefighting operation and rescue mission. A recent increasing concern is to develop self-powered fire warning materials that can be incorporated into the firefighting clothing to achieve active fire protection for firefighters before the protective clothing catches fire on fireground. However, it is still a challenge to facilely design and manufacture thermoelectric (TE) textile (TET)-based fire warning electronics with dynamic surface conformability and breathability. Here, we develop an alternate coaxial wet-spinning strategy to continuously produce alternating p/n-type TE aerogel fibers involving n-type Ti3C2Tx MXene and p-type MXene/SWCNT-COOH as core materials, and tough aramid nanofiber as protective shell, which simultaneously ensure the flexibility and high-efficiency TE power generation. With such alternating p/n-type TE fibers, TET-based self-powered fire warning sensors with high mechanical stability and wearability are successfully fabricated through stitching the alternating p-n segment TE fibers into aramid fabric. The results indicate that TET-based fire warning electronics containing 50 p-n pairs produce the open-circuit voltage of 7.5 mV with a power density of 119.79 nW cm-2 at a temperature difference of 300 °C. The output voltage signal is then calculated as corresponding surface temperature of firefighting clothing based on a linear relationship between TE voltage and temperature. The fire alarm response time and flame-retardant properties are further displayed. Such self-powered fire warning electronics are true textiles that offer breathability and compatibility with body movement, demonstrating their potential application in firefighting clothing.

Functional Materials and Innovative Strategies for Wearable Thermal Management Applications

Highlights

This article systematically reviews the thermal management wearables with a specific emphasis on materials and strategies to regulate the human body temperature. Thermal management wearables are subdivided into the active and passive thermal managing methods. The strength and weakness of each thermal regulatory wearables are discussed in details from the view point of practical usage in real-life.

Abstract

Thermal management is essential in our body as it affects various bodily functions, ranging from thermal discomfort to serious organ failures, as an example of the worst-case scenario. There have been extensive studies about wearable materials and devices that augment thermoregulatory functionalities in our body, employing diverse materials and systematic approaches to attaining thermal homeostasis. This paper reviews the recent progress of functional materials and devices that contribute to thermoregulatory wearables, particularly emphasizing the strategic methodology to regulate body temperature. There exist several methods to promote personal thermal management in a wearable form. For instance, we can impede heat transfer using a thermally insulating material with extremely low thermal conductivity or directly cool and heat the skin surface. Thus, we classify many studies into two branches, passive and active thermal management modes, which are further subdivided into specific strategies. Apart from discussing the strategies and their mechanisms, we also identify the weaknesses of each strategy and scrutinize its potential direction that studies should follow to make substantial contributions to future thermal regulatory wearable industries.

Reducing volume expansion in micro silicon anodes via aramid nanofibers for stable lithium-ion batteries

The aramid nanofibers form networks on micro silicon particles (ANF-SMPs) by cryofixation and acid-induced protonation, whose zongzi-like wrapping structure reduces volume expansion during (de)lithiation. The obtained ANF-SMP electrode achieves a high capacity retention of 90.7% after 100 cycles at 0.5C, which maps a promising future for anodes with a long lifespan.

High-Strength Magnetic Hydrogels with Photoweldability Made by Stepwise Assembly of Magnetic-Nanoparticle-Integrated Aramid Nanofiber Composites

Hydrogels capable of transforming in response to a magnetic field hold great promise for applications in soft actuators and biomedical robots. However, achieving high mechanical strength and good manufacturability in magnetic hydrogels remains challenging. Here, inspired by natural load-bearing soft tissues, a class of composite magnetic hydrogels is developed with tissue-mimetic mechanical properties and photothermal welding/healing capability. In these hydrogels, a hybrid network involving aramid nanofibers, Fe₃O₄ nanoparticles, and poly(vinyl alcohol) is accomplished by a stepwise assembly of the functional components. The engineered interactions between nanoscale constituents enable facile materials processing and confer a combination of excellent mechanical properties, magnetism, water content, and porosity. Furthermore, the photothermal property of Fe₃O₄ nanoparticles organized around the nanofiber network allows near-infrared welding of the hydrogels, providing a versatile means to fabricate heterogeneous structures with custom designs. Complex modes of magnetic actuation are made possible with the manufactured heterogeneous hydrogel structures, suggesting opportunities for further applications in implantable soft robots, drug delivery systems, human-machine interactions, and other technologies.

Smart Energy-Absorbing Aerogel-Based Honeycombs with Selectively Nanoconfined Shear-Stiffening Gel

Aerogels, shaped as fibers, films, as well as monoliths, have demonstrated a plethora of applications in both academia and industry due to charming properties including ultralow density, large specific surface area, high porosity, etc., however studies on more complicated aerogel forms (e.g., honeycombs) with more powerful applications have not been fully explored. Herein, the Kevlar aerogel honeycomb is firstly constructed through a dry ice-assisted 3D printing method, where the Kevlar nanofiber ink is printed directly in dry ice freezing atmosphere, followed by supercritical fluid drying. The subsequent 3D Kevlar/shear-stiffening gel (SSG) honeycomb (3D-KSH) can be obtained by selective nanoconfining of SSG into nanopores of the aerogel skeleton wall (with the loading amount of 93 wt%) rather than into open honeycomb channels, solving the leakage, creep deformation, and shape design infeasibility of the SSG. Combining the advantages of Kevlar, honeycomb and SSG, the fabricated 3D-KSH shows obvious smart responsive behavior to external stimulus. Additionally, the 3D-KSH has high strain rate sensitivity (sensitivity factor of 4.16 × 10^-4 ) and excellent impact protection performance (energy absorption value up to 176 J g^-1 at the strain rate of 6300 s^-1 ), which will significantly broaden application prospect in some intelligent protection fields.

Sheath-core structured Ca-alginate/PVA aerogel fibers via directed freezing wet-spinning

Biomass-based aerogel fibers have attracted increasing attention due to their renewable nature. However, their disadvantages, such as low mechanical strength, poor long-range order, and easy combustion, are still significant challenges. Herein, a directed freezing-assisted forced stretching strategy is developed to fabricate sheath-core structured Ca-alginate/polyvinyl alcohol (Ca-A/PVA) aerogel fibers with Long-range-ordered pores. The Ca-A/PVA aerogel fibers (3:2 m/m) exhibit the best comprehensive mechanical properties in terms of low thermal conductivity of 0.0524 W·m^-1·K^-1, a density of 0.1614 g·cm^-3, a porosity of 89.9 %, a tensile strength of 8.72 MPa, a tensile modulus of 249.7 MPa, a toughness of 1.98 MJ∙m^-3, and a self-extinguishing time from the fire of <1.2 s. The Ca-A/PVA fabrics showed a maximum absolute temperature difference of 11.4 °C at -20 °C and 14.0 °C at 60 °C compared to the plate temperature. The presented strategy is generalizable to other alginate-based aerogel fibers (e.g., alginate/guar gum).

The Effects of SiO2/Al2O3 and H2O/Al2O3 Molar Ratios on SAPO-34 Catalyst in the Methanol to Olefin Process

Informed through synthesis and characterization of NH ₃ TPD, BET techniques, the current study investigated the right contribution of silicon and water content on a 9 sample SAPO-34 catalyst with different molar ratios. The final prepared SAPO-34 catalytic performed reaction for the Methanol to olefin process was processed and reported at 410 0 C a reactor of fixed-bed. It was shown that catalysts with different SiO₂ /Al₂O₃ and H₂O/Al ₂ O ₃ ratios demonstrated high ethylene and propylene selectivity, due to their intensified crystallinity and size of crystals (1.3 to 1.7 μm). The highest degrees of ethylene and propylene selectivity for 3 samples were 50.25, 21.20, and 48.44, 19.16 respectively. Samples with ratios of different that possess high density and acute acidic sites to deactivate rapidly. The high density of acute acidic sites promoted the ultimate response to saturated hydrocarbons and aromatics based on olefins’ hydrogen transfer to and resulted in the coke generation on the top layer of the catalyst.

Bio-Inspired Aramid Fibers@silica Binary Synergistic Aerogels with High Thermal Insulation and Fire-Retardant Performance

Flame-retardant, thermal insulation, mechanically robust, and comprehensive protection against extreme environmental threats aerogels are highly desirable for protective equipment. Herein, inspired by the core (organic)-shell (inorganic) structure of lobster antenna, fire-retardant and mechanically robust aramid fibers@silica nanocomposite aerogels with core-shell structures are fabricated via the sol-gel-film transformation and chemical vapor deposition process. The thickness of silica coating can be well-defined and controlled by the CVD time. Aramid fibers@silica nanocomposite aerogels show high heat resistance (530 °C), low thermal conductivity of 0.030 W·m^-1·K^-1, high tensile strength of 7.5 MPa and good flexibility. More importantly, aramid fibers@silica aerogels have high flame retardancy with limiting oxygen index 36.5. In addition, this material fabricated by the simple preparation process is believed to have potential application value in the field of aerospace or high-temperature thermal protection.

Lipophilic Modified Hierarchical Multiporous rGO Aerogel-Based Organic Phase Change Materials for Effective Thermal Energy Storage

In the field of thermal energy storage, organic phase change materials (PCMs) are widely used as functional materials to boost thermal applications. However, there is often a tradeoff between constructing shape-stable composite PCMs with high enthalpy value and those with low leakage rates. Here, we proposed a promising scheme to address this issue. A novel hydrogel consisting of reduced graphene oxide (rGO) and covalent organic framework (COF) was prepared via hydrothermal methods, and the rGO-COF ultralight aerogel with a hierarchical porous structure was formed after freeze-drying. The rGO-COF aerogel shows excellent absorption ability and affinity for organic solvents. It can sufficiently adsorb the molten organic PCMs, such as polyethylene glycol (PEG), and synthesize shape-stable composite PCMs with excellent leak resistance. The COF grown on the surface of rGO has a superior affinity for PEG, so rGO-COF aerogel shows an outstanding PEG loading rate of up to 96.1 wt %, which is 1.7 wt % higher than that of rGO aerogel. In addition, the COF effectively reduces the subcooling of PEG/rGO-COF with 20.3%, compared to PEG/rGO. Meanwhile, the prepared PEG/rGO-COF exhibits extremely high enthalpy and relative enthalpy efficiency (164.6 J/g, 97.4%). This demonstrates that a promising direction was highlighte for the preparation of high-enthalpy shape-stable composite organic PCMs in this work.

Lignosulfonate valorization into a Cu-containing magnetically recyclable photocatalyst for treating wastewater pollutants in aqueous media

This study presents an eco-friendly and economical process for preparing a magnetic copper complex conjugated to modified calcium lignosulfonate (LS) through a diamine (Fe₃O₄@LS@naphthalene-1,5-diamine@copper complex; FLN-Cu) as a green and novel catalyst. The prepared catalyst was characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), Brunauer-Emmett-Teller (BET), energy-dispersive X-ray spectroscopy (EDS), elemental mapping, inductively coupled plasma-optical emission spectrometry (ICP-OES) and field emission scanning electron microscopy (FESEM) techniques. The photocatalytic performance of the synthesized FLN-Cu catalyst was investigated by the degradation of aqueous solutions of dyes such as Rhodamine B (RhB), methylene blue (MB), and Congo red (CR) under UV irradiation. The dye degradation was followed by UV-Vis (ultraviolet-visible) spectrophotometry by measuring the changes in absorbance. The effects of different factors such as pH, contact time, photocatalyst dosage, and initial concentration of dye on the adsorption percentage were also investigated. Moreover, the catalyst showed high stability and could be readily separated from the reaction media using a magnet and reused five times without a remarkable loss of catalytic ability.

Nanoscale Kevlar Liquid Crystal Aerogel Fibers

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 via 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^-1·K^-1), 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.

The Aramid-Coating-on-Aramid Strategy toward Strong, Tough, and Foldable Polymer Aerogel Films

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 para-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.

A flexible, robust and multifunctional montmorillonite/aramid nanofibers@MXene electromagnetic shielding nanocomposite with an alternating structure for enhanced Joule heating and fire-resistant protective performance

With the rapidly increasing development of portable devices and flexible electronic devices, multifunctional composites with excellent mechanical strength, great electromagnetic interference shielding, great Joule heating performance and strong fire-resistant protective performance are noticeably required. Herein, inspired by the sandwich structure, we have designed a montmorillonite/aramid nanofibers@MXene (MMT/ANFs@MXene) nanocomposite with an alternating multilayered structure via a simple AVF process. In this nanocomposite, the ANFs/MMT (AT) layer acts as a mechanically reinforced and insulation protection layer, while the MXene layer maintains a complete conductive network. The superior alternating multilayered structure endows the nanocomposite with outstanding mechanical properties (154.66 MPa, 14.22%) and excellent EMI shielding effectiveness values (58.4 dB). In addition, the fire-resistant protective performance of the nanocomposite improves its safety and reliability, especially, the EMI shielding effectiveness is maintained at ∼34 dB after burning for 30 s. Besides, the MMT/ANFs@MXene nanocomposite shows excellent Joule heating performance with a fast thermal response, low driving voltage and long-time temperature stability, which could reach 110.2 °C at only 3 V applied voltage within 10 s. As a result, this work presents a novel strategy for constructing multifunctional composites with outstanding overall performance, which will broaden application areas and prospects in thermal management and EMI shielding in wearable products.

Mixed Biopolymer Systems Based on Bovine and Caprine Caseins, Yeast β-Glucan, and Maltodextrin for Microencapsulating Lutein Dispersed in Emulsified Lipid Carriers

Lutein is an important antioxidant that quenches free radicals. The stability of lutein and hence compatibility for food fortification is a big challenge to the food industry. Encapsulation can be designed to protect lutein from the adverse environment (air, heat, light, pH). In this study, we determined the impact of mixed biopolymer systems based on bovine and caprine caseins, yeast β-glucan, and maltodextrin as wall systems for microencapsulating lutein dispersed in emulsified lipid carriers by spray drying. The performance of these wall systems at oil/water interfaces is a key factor affecting the encapsulation of lutein. The highest encapsulation efficiency (97.7%) was achieved from the lutein microcapsules prepared with the mixed biopolymer system of caprine αs1-II casein, yeast β-glucan, and maltodextrin. Casein type and storage time affected the stability of lutein. The stability of lutein was the highest (64.57%) in lutein microcapsules prepared with the mixed biopolymer system of caprine αs1-II casein, yeast β-glucan, and maltodextrin, whereas lutein microcapsules prepared with the biopolymer system of bovine casein, yeast β-glucan, and maltodextrin had the lowest (56.01%). The stability of lutein in the lutein microcapsules dramatically decreased during storage time. The antioxidant activity of lutein in the lutein microcapsules was closely associated with the lutein concentration.

Electrospun Ta-MOF/PEBA Nanohybrids and Their CH4 Adsorption Application

For the first time, biocompatible and biodegradable Ta-metal organic framework (MOF)/polyether block amide (PEBA) fibrous polymeric nanostructures were synthesized by ultrasonic and electrospinning routes in this study. The XRD peaks of products were wider, which is due to the significant effect of the ultrasonic and electrospinning methods on the final product. The adsorption/desorption behavior of the nanostructures is similar to that of the third type of isotherm series, which showed mesoporous behavior for the products. The sample has uniform morphology without any evidence of agglomeration. Since the adsorption and trapping of gaseous pollutants are very important, the application of the final Ta-MOF/PEBA fibrous polymeric nanostructures was investigated for CH4 adsorption. In order to achieve the optimal conditions of experiments and also systematic studies of the parameters, fractional factorial design was used. The results showed that by selecting temperature 40°C, time duration 35 min, and pressure 3 bar, the CH4 gas adsorption rate was near 4 mmol/g. Ultrasonic and electrospinning routes as well as immobilization of Ta-MOF in the PEBA fibrous network affect the performance of the final products for CH4 gas adsorption.

A Temperature-Sensitive Polymeric Rheology Modifier Used in Water-Based Drilling Fluid for Deepwater Drilling

Rheology modifiers are essential for the flat rheology of water-based drilling fluids in deepwater. The low temperature thickening of deepwater water-based drilling fluids results in dramatic rheological changes in the 20–30 °C range. To address such problems, NIPAM with a self-polymerized product LCST of 32–35 °C was selected as the main body for synthesis. While introducing the hydrophilic monomer AM to enhance the thickening properties, the hydrophobic monomer BA was selected to reduce the LCST of the product. In this paper, a temperature-sensitive polymeric rheology modifier (PNBAM) was synthesized by emulsion polymerization using N-isopropyl acrylamide, acrylamide, and butyl acrylate as monomers. The PNBAM was characterized using infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and nuclear magnetic resonance hydrogen spectroscopy (NMR). The rheological properties, temperature resistance, and salt resistance of PNBAM in the base fluid (BF) were tested. The performance of PNBAM in the drilling fluid system was also evaluated, and a water-based drilling fluid system of flat rheology for deepwater was formulated. The rheological modification mechanism of PNBAM was analyzed by turbidity analysis, particle size analysis, and zeta analysis. Experimental results show that PNBAM has good rheological properties. PNBAM is temperature resistant to 150 °C, salt-resistant to 30 wt%, and calcium resistant to 1.0 wt%. PNBAM also has good flat rheology characteristics in drilling fluid systems: AV_4°C:AV_25°C = 1.27, PV_4°C:PV_25°C = 1.19. Mechanistic analysis showed that the LCST (Lower Critical Solution Temperature) of 0.2 wt% PNBAM in an aqueous solution was 31 °C. Through changes in hydrogen bonding forces with water, PNBAM can regulate its hydrophilic and hydrophobic properties before and after LCST, which thus assists BF to achieve a flat rheological effect. In summary, the temperature-sensitive effect of PNBAM has the property of enhancing with increasing temperature. While the tackifying effect of conventional rheology modifiers diminishes with increasing temperature, the temperature-sensitive effect of PNBAM gives it an enhanced thickening effect with increasing temperature, making it a more novel rheology modifier compared to conventional treatment additives. After LCST, compared to conventional rheology modifiers (XC), PNBAM has a more pronounced thermo-thickening effect, improving the main rheological parameters of BF by more than 100% or even up to 200% (XC less than 50%). This contributes to the flat rheology of drilling fluids. PNBAM has good application prospects and serves as a good reference for the development of other rheology modifiers.