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The main uses of bullets are as projectiles in firearms for military, law enforcement, and civilian purposes. However, bullets have significant industrial applications beyond their role in weaponry, such as precision drilling, cutting, and shaping of hard materials. Steel bullets have a very resistant structure and will not be damaged if exposed to corrosion. Other applications that are resistant to strike and projectiles, such as the automotive and aerospace industries, are based on fibers or fabrics with high toughness and tensile strength, such as Kevlar and p -aramid fibers, which are impregnated with some thermoplastic or thermoset polymers. Therefore, in the upcoming research, the impact of external force (EF) with various values (0.1, 0.2, 0.3, 0.4, and 0.5 V/Å) on the strength of Kevlar nanofibers reinforced with silicon dioxide (SiO2) nanoparticles and ethylene glycol (EG) has been investigated using LAMMPS software. EG and SiO2 nanoparticles with 10 and 2 vol% were added to Kevlar fabrics, creating a shear thickening fluid (STF) nanocomposite. The energy parameters of the interaction between the particles, collision velocity, and the center of mass have been calculated. The findings of the research indicate an increase in the interaction energy from 111271.85 to 154351.15 kcal/mol, an increase in the collision velocity from 0.7046 to 1.5812 Å/fs and an increase in the center of mass from 0.62671 to 1.1670 Å due to the EF applied from 0.2 to 0.4 (kcal/mol)/Å. These results show EF should be optimized in actual cases for the collision process to occur effectively.

The flexible proton exchange membrane (PEM) was constructed through alternate deposition of Kevlar nanofibers and polydopamine (PDA)-coating polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) with spin coating technology. In the prepared (Kevlar/PDA@SEBS)5 membrane, the Kevlar nanofibers could withstand the external mechanical force owing to the fiber structure, while the flexible PEM was folded or stretched. The adhesive PDA coating was formed with the self-polymerization of dopamine protected the molecular chains of SEBS and further supported the flexible PEM. The structure of PDA coating SEBS could avoid the microstructure fracture of the flexible PEM during the folding and stretching operations. Notably, the multilayered structure promoted the phosphoric acid (PA) molecules motion through reducing the ion conduction resistance. For instance, the pristine (Kevlar/PDA@SEBS)5/PA membrane exhibited the proton conductivity of 4.11 × 10–2 S/cm at 160 °C, which was comparable to 4.13 × 10–2 S/cm of the folded membrane and (4.07–4.78) × 10–2 S/cm of the stretched membranes. The stable microstructure guaranteed the stiffness, such as 4.15 MPa of the (Kevlar/PDA@SEBS)5-fold/PA membrane and (3.50–6.34) MPa of (Kevlar/PDA@SEBS)5-stretched/PA membranes. Furthermore, the stretched membrane possessed the long-term proton conductivity stability, which was indicative of the microstructure and component stabilities. [ABSTRACT FROM AUTHOR]

The imidazolium ionic liquid of (Kevlar/bmimCl/SEBS) 5 membrane was immobilized in flexible proton exchange membranes (PEMs) with the spin coating technology. In the prepared (Kevlar/bmimCl/SEBS) 5 membrane, the imidazolium ionic liquid of 1-butyl-3-methylimidazolium chloride (bmimCl) functioned as glue to modify the microstructure fracture from the stretching operation through occupying the cracks. The proton conduction resistance was reduced with the well-ordered distribution of components in the multilayered microstructure. Although the doped phosphoric acid (PA) molecules charged the proton conductivity, the imidazolium cations of bmim+ could participate in the proton conduction through the formation of continuous proton conduction channels. In this research, the folding and stretching operations exerted the negligible effect on microstructure and property of the prepared PEMs. Besides the modification of bmimCl, the deformation of polystyrene- block -poly(ethylene- ran -butylene)- block -polystyrene (SBES) molecular chains and Kevlar nanofibers in the stretching operation contributed to maintain the stable microstructure. The stretching and folding operations led to slight variation on the membrane property. Specifically, the proton conductivities were respectively 3.21 × 10−2 S/cm and 4.16 × 10−2 S/cm at 160 °C, which were even superior to 2.77 × 10−2 S/cm of the pristine membranes. Furthermore, the tensile stress values of the folding and stretching membranes can reach (18.9 ± 1.19) MPa and (32.6 ± 2.63) MPa. [Display omitted] • Flexible proton exchange membranes were constructed. • Ionic liquid modified microstructure fracture of stretching membranes. • High and stable proton conductivity was obtained. [ABSTRACT FROM AUTHOR]

The emerging wearable electronics and e‐textiles have motivated tremendous interests in textile energy storage microdevices. Among them, fiber‐shaped capacitors (FSCs) offer unique properties because of their 1D configuration and reliable energy storage. In recent years, many works focused on the development of 1D fibrous‐shaped electrodes usually involving complex material synthesis and techniques. Herein, an easy procedure for the preparation of composite fibers made by PEDOT:PSS infiltration in gel‐state Kevlar nanofiber (KNF) wires is proposed. The PEDOT:PSS@KNF 1D electrodes are mechanically robust, conductive, and flexible. The symmetric FSCs integrated in textile show remarkable capacitance retention under deformation, average capacitance of 1.1 mF, volumetric energy density of 71 mWh cm−3, and ability to power on a blue light‐emitting diode. [ABSTRACT FROM AUTHOR]

The well-ordered microstructure has been demonstrated to accelerate the proton conduction process through reducing proton conduction resistance. In this research, the proton exchange membranes (PEMs) with sandwich-like microstructure have been constructed based on Kevlar nanofibers and bifunctional nanofibers of chitosan (CS) with polyvinyl alcohol (PVA). The CS/PVA bifunctional nanofibers (CPNF) layer has been prepared with electrospinning process, which is stably adhered to the Kevlar nanofibers layer owing to compatible interfacial property. The fine structure stability without layer separation is achieved even with phosphoric acid (PA) molecules doping in the prepared PA doped composite membranes. The fibrous microstructure accelerats proton conduction through regulating proton conduction pathways. The objective of accelerating proton conduction at subzero temperature has been realized, reflecting in high and stable proton conductivities. For instance, the (Kevlar/CPNF/Kevlar)/PA membrane exhibits proton conductivities of 9.75 × 10−3 S/cm at −30 °C and 8.22 × 10−2 S/cm at 30 °C. Most importantly, the fine proton conductivity stability is identified by the results of the cycle test and long-term test. Specifically, the proton conductivities are respectively 8.62 × 10−3 S/cm at −30 °C and 8.07 × 10−2 S/cm at 30 °C after a five heating/cooling cycle process. The proton conductivities remain 2.97 × 10−2 S/cm at −25 °C and 7.19 × 10−2 S/cm at 30 °C after a 1032 h non-stop test. Additionally, the single proton exchange membrane fuel cell with the (Kevlar/CPNF/Kevlar)/PA membrane exhibits the peak power densities of 279.5 mW/cm2 at 100 °C and 352.7 mW/cm2 at 130 °C. [Display omitted] • Bifunctional nanofibers were used to construct proton exchange membranes. • Accelerating proton conduction at subzero temperature was achieved. • Conductivity reached 2.97 × 10−2 S/cm at −30 °C after a 1015 h non-stop test. [ABSTRACT FROM AUTHOR]

Successive proton conduction channels are constructed with the spin coating method in flexible proton exchange membranes (PEMs). In this research, phosphoric acid (PA) molecules are immobilized in the multilayered microstructure of Kevlar nanofibers and polystyrene- block -poly(ethylene- ran -butylene)- block -polystyrene (SEBS) polymer molecular chains. As a result, successive proton conduction channels can accelerate the proton conduction process in the prepared membrane with the multilayered microstructure. Additionally, the microstructure fractures of the composite membranes from the external force of folding and stretching operations are modified by the inner PA molecules. Notably, numerous PA molecules are further combined through formed intermolecular hydrogen bonding. The stretched membrane absorbs more PA molecules owing to the arrangement of PA molecules, Kevlar nanofibers, and SEBS molecular chains. The stretched membrane thus exhibits the enhanced proton conduction ability, such as the through-plane proton conductivity of 1.81 × 10 -1 S cm -1 at 160 °C and that of 4.53 × 10 -2 S cm -1 at 120 °C lasting for 600 h. Furthermore, the tensile stress of PA-doped stretched membranes reaches (3.91 ± 0.40)-(6.15 ± 0.43) MPa. A single proton exchange membrane fuel cell exhibits a peak power density of 483.3 mW cm -2 at 120 °C.

Summary: Freeze‐drying (fd) technique is an effective and facile method to accumulate nanofibers for membrane preparation, and it has been frequently reported in the development of energy materials. Kevlar as amide nanofibers (ANFs) could serve as support materials for proton exchange membranes (PEMs) owing to the merits of exceptional stiffness and strength, etc. The aim of this research is to enhance the proton conductivity of phosphoric acid (PA)‐doped Kevlar membranes by incorporating polyacrylamide (PAM) and 1‐butyl‐3‐methylimidazolium chloride (bmimCl) with freeze‐drying technique. The components of PAM and bmimCl could provide the binding sites to combine PA molecules with the formation of Kevlar/PAM/bmimCl/PA membranes. Furthermore, the prepared membranes with the freeze‐drying posttreatment are substantially more effective at enhancing proton conductivity owing to the combination of more PA molecules. Specifically, Kevlar/PAM/bmimCl(fd)/PA membranes showed the anhydrous proton conductivity of 2.64 × 10−1 S/cm at 180°C and 1.04 × 10−1 S/cm at 140°C in a 270‐hour non‐stop test. As regard to the prepared PA‐doped Kevlar/CdTe‐based membranes, the mechanical strength was far from what was expected. Comparing to the solution casting method, the freeze‐drying technique was a feasible strategy to deal with ANFs for exploiting high‐temperature PEMs with high performance. [ABSTRACT FROM AUTHOR]

Hemostatic materials have played a significant role in mitigating traumatic injury by controlling bleeding, however, the fabrication of the desirable material's structure to enhance the accumulation of blood cells and platelets for highly efficient hemostasis is still a great challenge. In this work, directed assembly of poly(vinyl alcohol) (PVA) macromolecules covering the rigid Kevlar nanofiber (KNF) network during 3D printing process is utilized to fabricate hydrophilic, biocompatible, and mechanically stable KNF-PVA aerogel filaments for effective enriching blood components by fast water absorption. As such, KNF-PVA aerogel gauzes demonstrate remarkable water permeability (338 mL cm -2 s -1 bar -1 ), water absorption speed (as high as 9.64 g g -1 min -1 ) and capacity (more than ten times of self-weight), and ability to enrich micron-sized particles when contacting aqueous solution. All these properties favor efficient hemostasis and the resulting KNF-PVA aerogel gauzes significantly outperform the commercial product Quikclot Gauze (Z-Medica) during in vivo experiments with the rat liver laceration model, reducing the hemostasis time by half (60 ± 4 s) and the blood loss by two thirds (0.07 ± 0.01 g). These results demonstrate a robust strategy to design various aerogel gauzes for hemostasis applications., (© 2022 The Authors. Advanced Healthcare Materials published by Wiley-VCH GmbH.)

Aerogels, the lightest artificial solid materials characterized by low density and thermal conductivity, high porosity, and large specific surface area, have attracted increasing interest. Aerogels exhibit single-mode thermal insulation properties regardless of the surrounding temperature. In this study, hyperelastic Kevlar nanofiber aerogels (HEKAs) are designed and fabricated by a slow-proton-release-modulating gelation and thermoinduced crosslinking strategy. The method does not use crosslinking agents and endows the ultralow-density (4.7 mg cm -3 ) HEKAs with low thermal conductivity (0.029 W m -1 K -1 ), high porosity (99.75%), high thermal stability (550 °C), and increased compression resilience (80%) and fatigue resistance. Proofs of the concept of the HEKAs acting as on-off thermal switches are demonstrated through experiments and simulations. The thermal switches exhibit a rapid thermal response speed of 0.73 °C s -1 , high heat flux of 2044 J m -2 s -1 , and switching ratio of 7.5. Heat dissipation can be reversibly switched on/off more than fifty times owing to the hyperelasticity and fatigue resistance of the HEKAs. This study suggests a route to fulfill the hyperelasticity of highly porous aerogels and to tailor heat flux on-demand., (© 2022 Wiley-VCH GmbH.)

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.

[Display omitted] • Multilayered membranes were prepared with vacuum assisted flocculation. • Proton conductivity reaches 2.80 × 10-2 S/cm at −30 °C. • Low temperature proton conduction mechanism was discussed. The application of proton exchange membranes in low temperature proton exchange membrane fuel cells requires the quick and stable proton conduction at subzero temperature. In this research, we constructed the multilayered membranes through the alternate deposition of poly(vinyl alcohol) (PVA), Kevlar nanofibers and carbon nanotube oxides (OCNTs) through the vacuum assisted flocculation (VAF) technique. The intermolecular hydrogen bonds resulted in the preparation of (PVA/Kevlar/OCNTs) 3 membranes with layered structure. Phosphoric acid (PA) molecules entered the gaps between the neighboring layers accompanying with the phase separation. The prepared membranes exhibited the high and stable proton conductivity at subzero temperature, such as 2.04 × 10-2 S/cm at −30 °C and 1.52 × 10-1 S/cm at 30 °C. The proton conductivity gradually changed to 5.52 × 10-2 S/cm and 1.84 × 10-1 S/cm even after the ten-cycles process of −30 °C–30 °C. In addition, the value can retain 1.42 × 10-2 S/cm at −30 °C in a 1900 h non-stop test. The evaporation and liquefaction of water molecules could affect proton conductivity besides PA dominating the proton conduction behavior during heating/cooling processes. Furthermore, the balance on low temperature proton conduction and mechanical strength makes the multilayered (PVA/Kevlar/OCNTs) 3 /PA membranes as a promising PEM candidate at subzero temperature. [ABSTRACT FROM AUTHOR]

Aerogel films with a low density are ideal candidates to meet lightweight application and have already been used in a myriad of fields; however, their structural design for performance enhancement remains elusive. Herein, we put forward a laminated structural engineering strategy to prepare a free-standing carbon nanotube (CNT)-based aerogel film with a densified laminated porous structure. By directional densification and carbonization, the three-dimensional network of one-dimensional nanostructures in the aramid nanofiber/carbon nanotube (ANF/CNT) hybrid aerogel film can be reconstructed to a laminated porous structure with preferential orientation and consecutively conductive pathways, resulting in a large specific surface area (341.9 m 2 /g) and high electrical conductivity (8540 S/m). Benefiting from the laminated porous structure and high electrical conductivity, the absolute specific shielding effectiveness (SSE/ t ) of a CNT-based aerogel film can reach 200647.9 dB cm 2 /g, which shows the highest value among the reported aerogel-based materials. The laminated CNT-based aerogel films with an adjustable wetting property also exhibit exceptional Joule heating performance. This work provides a structural engineering strategy for aerogel films with enhanced electric conductivity for lightweight applications, such as EMI shielding and wearable heating.

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.