High-density Fibrous Polyimide Sponges with Superior Mechanical and Thermal Properties

Unraveling the Impact of Boron Nitride and Silicon Nitride Nanoparticles on Thermoplastic Polyurethane Fibers and Mats for Advanced Heat Management

The urgent challenges posed by the energy crisis, alongside the heat dissipation of advanced electronics, have embarked on a rising demand for the development of highly thermally conductive polymer composites. Electrospun composite mats, known for their flexibility, permeability, high concentration and orientational degree of conductive fillers, stand out as one of the prime candidates for addressing this need. This study explores the efficacy of boron nitride (BN) and its potential alternative, silicon nitride (SiN) nanoparticles, in enhancing the thermal performance of the electrospun composite thermoplastic polyurethane (TPU) fibers and mats. The 3D reconstructed models obtained from FIB-SEM imaging provided valuable insights into the morphology of the composite fibers, aiding the interpretation of the measured thermal performance through scanning thermal microscopy for the individual composite fibers and infrared thermography for the composite mats. Notably, we found that TPU-SiN fibers exhibit superior heat conduction compared to TPU-BN fibers, with up to a 6 °C higher surface temperature observed in mats coated on copper pipes. Our results underscore the crucial role of arrangement of nanoparticles and fiber morphology in improving heat conduction in the electrospun composites. Moreover, SiN nanoparticles are introduced as a more suitable filler for heat conduction enhancement of electrospun TPU fibers and mats, suggesting immense potential for smart textiles and thermal management applications.

Ionic Liquid Directed Spinning of Cellulose Aerogel Fibers with Superb Toughness for Weaved Thermal Insulation and Transient Impact Protection

Aerogel fibers, combining the nanoporous characteristics of aerogels with the slenderness of fibers, have emerged as a rising star in nanoscale materials science. However, endowing nanoporous aerogel fibers with good strength and high toughness remains elusive due to their high porosity and fragile mechanics. To address this challenge, this paper reports supertough aerogel fibers (SAFs) initially started from ionic-liquid-dissociated cellulose via wet-spinning and supercritical drying in sequence. The supertough nanoporous aerogel fibers assembled with cellulose nanofibers exhibit a high specific surface area (372 m2/g), good mechanical strength (30 MPa), and large elongation (107%). Benefiting from their high strength and elongation, the resultant cellulose nanoporous aerogel fibers show ultrahigh toughness up to 21.85 MJ/m3, much outperforming the known aerogel materials in the literature. Moreover, the toughness of this nanoporous aerogel fiber is 7.4 times higher than that of human knee ligaments, and its specific toughness is comparable to that of commonly used solid polyester fibers. In addition, we also verified the weavability, desirable thermal insulation performance, and supertoughness to resist the transient impact of SAFs. The long-sought strategy to simultaneously resolve the strength and toughness of nanoporous aerogel fibers, in combination with the biodegradable nature of the cellulose, provides multifaceted opportunities for broad potential applications, including lightweight wearable textiles and beyond.

Improvement of the Mechanical Properties of Silica Aerogels for Thermal Insulation Applications through a Combination of Aramid Nanofibres and Microfibres

Reinforcement of silica aerogels, remarkable lightweight mesoporous materials with outstanding insulation performance, is still a challenging research topic. Among the strategies used to overcome their brittleness, one of the most effective is the manufacturing of aerogel composites with embedded fibres. In this work, the incorporation of nanofibres together with microfibres in a tetraethoxysilane-vinyltrimethoxysilane matrix is investigated for the first time for the development of novel aerogel nanocomposites. The nanofibres, synthesized from different aramid fibres, including Kevlar^® pulp, Technora^®, Teijinconex^® and Twaron^® fibres, were used in different combinations with microaramids and the resulting nanocomposites were thoroughly investigated for their physicochemical and thermomechanical features. The properties depended on the type and amount of the nano/microfibre used. While the microfibres exhibited low interaction with the silica matrix, the higher surface of the nanofibres ensured increased contact with the gel matrix. A low bulk density of 161 kg m^-3 and thermal conductivity of 38.3 mW m^-1 K^-1 (Hot Disk^®) was achieved when combining the nanofibres obtained from Kevlar^® pulp with the Technora^® or Teijinconex^® long fibres. The nanofibres showed higher dispersion and random orientation and in combination with microfibres led to the improvement by a factor of three regarding the mechanical properties of the aerogel nanocomposites reinforced only with microfibres. The scale-up process of the samples and simulated tests of thermal cycling and vacuum outgassing successfully conducted indicate good compliance with space applications.

Fabrication of Textile Waste Fibers Aerogels with Excellent Oil/Organic Solvent Adsorption and Thermal Properties

In recent years, the treatment of textile waste has attracted more and more attention around the world. The reuse of textile waste can contribute to the reduction of carbon emissions and the sustainable development of the economy. Herein, we proposed a facile and cost-effective approach to fabricating aerogel by using textile waste fibers as the matrix and polyvinyl alcohol (PVA) and glutaraldehyde (GA) as crosslinking agents. After being modified with methyltrimethoxysilane (MTMS) via chemical vapor deposition, both the interior and exterior of the textile waste aerogels exhibit a hydrophobic property with a water contact angle of up to 136.9° ± 2.3°. A comprehensive investigation of the structure, thermal properties, mechanical properties and oil absorption capacity of this aerogel shows its potential for building insulation and oil spill cleanup. The textile waste fibers aerogels have low density and high porosity, good thermal stability and outstanding heat insulation properties (K_avg. = 0.049–0.061 W/m·K). With a maximum oil absorption value of 26.9 ± 0.6 g/g and rapid and effective oil/water mixture separation, the aerogel exhibits competitive commercial application value.

Surface Modification on Polyimide Yarn by Plasma Treatment to Enhance Adhesion with Polypropylene Resin

Polyimide yarn as a kind of high performance fiber material has to improve the adhesion between the material surface and the resin in order to get a deeper application. The surface of polyimide yarn is modified by low temperature plasma treatment, and the effect of plasma treatment parameters on the adhesion between polyimide yarn and polypropylene resin is studied. By comparing the extraction force on the surface of polyimide yarn before and after treatment, the effect of plasma treatment parameters such as treatment time, processing gas and treating power on yarn adhesion is investigated. Furthermore, the adhesive force between polyimide yarn and polypropylene resin is analyzed by a single factor to optimize the process parameters to obtain higher adhesive force. Additionally, the Box-Behnken design is utilized to optimize the plasma treatment parameters, and the significance of the influence of the plasma treatment parameters on the adhesion between the polyimide fiber and the resin is discussed. The optimal process parameters are obtained through analysis: the treatment time 90 s, the processing gas oxygen, and the treating power 150 W.

Organic–Inorganic Double-Gel System Thermally Insulating and Hydrophobic Polyimide Aerogel

Aerogel materials are used in various fields, but there is a shortage of aerogel materials with an excellent combination of mechanical properties, thermal stability, and easy preparation. In this study, polyimide aerogel materials with superior mechanical properties, thermal stability, and low thermal conductivity were prepared by forming a double-gel system in the liquid phase. The amino-modified gel, prepared by coating SiO₂ nano-microspheres with GO through a modified sol-gel method (SiO₂@GO-NH₂), was subsequently homogeneously dispersed with PAA wet gel in water to form a double-gel system. The construction of a double-gel system enabled the PI aerogel to shape a unique honeycomb porous structure and a multi-layered interface of PI/SiO₂/GO. The final obtained PI aerogel possessed effective thermal conductivity (0.0309 W/m·K) and a high specific modulus (46.19 m²/s²). In addition, the high thermal stability (543.80 °C in Ar atmosphere) and the ability to retain properties under heat treatment proved its durability in high thermal environments. The hydrophobicity (131.55°) proves its resistance to water from the environment. The excellent performance of this PI aerogel and its durability in thermal working environments make it possible to be applied in varied industrial and research fields, such as construction and energy, where heat and thermal insulation are required.

The Effect of Silane Coupling Agent on the Texture and Properties of In Situ Synthesized PI/SiO2 Nanocomposite Film

PI/SiO2 composite films have been prepared by using in situ polymerization. The influences of the dosage of silane coupling agent (KH-560) on the structure and performance of PI/SiO2 composite film have been investigated. The results show that in the components without KH-560, the addition of SiO2 decreases the transmittance of the sample. Compared to the same SiO2 doping amount, the transmittance in the visible light range of the sample using KH-560 is higher than that of the sample without KH-560. After adding KH-560, the tensile strength, the elastic modulus the elongation at break of the sample have largely changed. The thermal stability and the ability to resist ultraviolet radiation of the composite film first increases and then decreases. Furthermore, the optimal dosage of KH-560 is 3%. Moreover, the addition of KH-560 has little effect on the transmittance of the PI/SiO2 composite films before and after UV irradiation.

Superelastic and Fire-Retardant Nano-/Microfibrous Sponges for High-Efficiency Warmth Retention

Warmth retention equipment for personal cold protection is highly demanded in freezing weather; however, most present warmth retention materials suffer from high thermal conductivity, weak mechanical properties, and strong flammability, resulting in serious security risks. Herein, we report a facile strategy to fabricate nano-/microfibrous sponges with superelasticity, robust flame retardation, and effective warmth retention performance via direct electrospinning. The three-dimensional fluffy sponges with low volume density and high porosity are constructed by accurately regulating the relative humidity; meanwhile, the mechanically robust polyamide-imide nanofibers with high limit oxygen index (LOI) are innovatively introduced to improve the structural stability and flammability of the nano-/microfibrous sponges. Strikingly, the developed nano-/microfibrous sponges exhibit ultralight characteristics (6.9 mg cm^-3), superelasticity (∼0% plastic deformation after 100 compression tests), effective flame retardant with LOI of 26.2%, and good heat preservation ability (thermal conductivity of 24.6 mW m^-1 K^-1). This work may shed light on designing superelastic and flame-retardant warmth retention materials for various applications.

In-situ ZnO template preparation of coal tar pitch-based porous carbon-sheet microsphere for supercapacitor

Three-dimension (3D) porous carbon-sheet microspheres (PCSMs) are prepared through coating coal tar pitch on basic zinc carbonate microspheres followed by in situ ZnO template carbonization and KOH activation. The as-prepared PCSMs show microsphere morphology composed of petal-like carbon nanosheets, which have large specific area (1359.88-2059.43 m² g^-1) and multiscale pores (mainly micropores and mesopores). As the supercapacitor electrodes, the 3D PCSMs present a good electrochemical performance with a large specific capacitance of 313 F g^-1 at 1 A g^-1 and high rate capability of 81.9% capacitance retention when increasing the current density up to 50 A g^-1 in a three-electrode system. In addition, the energy density can reach up to 18.79 Wh kg^-1 at a high power density of 878.4 W kg^-1 for PCSMs-0.2a symmetrical supercapcitor in 1 M Na₂SO₄ electrolyte.

Recent Advances on Conducting Polymers Based Nanogenerators for Energy Harvesting

With the rapid growth of numerous portable electronics, it is critical to develop high-performance, lightweight, and environmentally sustainable energy generation and power supply systems. The flexible nanogenerators, including piezoelectric nanogenerators (PENG) and triboelectric nanogenerators (TENG), are currently viable candidates for combination with personal devices and wireless sensors to achieve sustained energy for long-term working circumstances due to their great mechanical qualities, superior environmental adaptability, and outstanding energy-harvesting performance. Conductive materials for electrode as the critical component in nanogenerators, have been intensively investigated to optimize their performance and avoid high-cost and time-consuming manufacture processing. Recently, because of their low cost, large-scale production, simple synthesis procedures, and controlled electrical conductivity, conducting polymers (CPs) have been utilized in a wide range of scientific domains. CPs have also become increasingly significant in nanogenerators. In this review, we summarize the recent advances on CP-based PENG and TENG for biomechanical energy harvesting. A thorough overview of recent advancements and development of CP-based nanogenerators with various configurations are presented and prospects of scientific and technological challenges from performance to potential applications are discussed.

Facile strategy to prepare polyimide nanofiber assembled aerogel for effective airborne particles filtration

Polyimide nanofiber (PINF) aerogel materials have received extensive attention as heat insulation, sensors and filtration media due to their excellent thermodynamic properties and unique porous structure. However, PINF must be difficult to disperse in organic solvents (dioxane or dimethyl sulfoxide) and dimensional instability has been regarded as issues that limits the preparation of PINF aerogels, especially in the water. So, it is of great significance to prepare polyimide aerogels with stable structure using water as a dispersant. In this work, the electrospun polyimide nanofiber precursor (polyamic acid (PAA) nanofiber (PAANF)) is uniformly dispersed in water, and triethylamine is added to terminated PAA oligomer as a binder. The resultant PINF aerogel has excellent mechanical properties with outstanding elasticity and a maximum compressive stress of 7.03 kpa at 50% strain. Furthermore, due to the extremely high porosity (98.4%) and hierarchical porous structure, the aerogel exhibits a high filtration efficiency (99.83%) for PM2.5, while the pressure drop is lower than that of the corresponding nanofiber membrane materials, which will facilitate its application in high temperature filtration and other fields.

Multifunctional Flame-Retardant Melamine-Based Hybrid Foam for Infrared Stealth, Thermal Insulation, and Electromagnetic Interference Shielding

Multifunctionalization is an important development direction of electromagnetic interference (EMI)-shielding materials. However, it is still a huge challenge to effectively integrate multiple functions into materials. Herein, we reported a facile method to fabricate multifunctional EMI-shielding materials, which were assembled with multidimensional components consisting of a 3D melamine-formaldehyde (MF) foam skeleton, 0D ferroferric oxide (Fe₃O₄) nanoparticles, and 1D silver nanowires (AgNWs) via coprecipitation and dip-coating processes. Due to the coaction of conductive AgNWs and magnetic Fe₃O₄ nanoparticles, the resultant hybrid foam showed excellent absorption-dominant EMI-shielding performances with a high specific EMI-shielding effectiveness value of 12,704 dB cm² g^-1. Moreover, thanks to the multilayer porous micro-/nanostructure and the nonflammability of functional coatings, the hybrid foam shows excellent flame retardancy and heat insulation, making it attractive for the functions of infrared stealth and heat insulation. The corresponding mechanism is discussed in detail. Combined with the advantages of high thermal insulation, flame retardancy, elasticity, and excellent absorption-dominant EMI-shielding performances, the hybrid foam showed great applications in the fields of both military and civilian. This work provides new inspiration and insights for the design of multifunctional high-performance EMI-absorbing materials.

Antibiofouling Ultrathin Poly(amidoxime) Membrane for Enhanced U(VI) Recovery from Wastewater and Seawater

Although eco-friendly amidoxime-based adsorbents own an excellent uranium (U)-adsorption capacity, their U-adsorption efficiency is commonly reduced and even damaged by the biological adhesion from bacteria/microorganisms in an aqueous environment. Herein, we present an antibiofouling ultrathin poly(amidoxime) membrane (AUPM) with highly enhanced U-adsorption performance, through dispersing the quaternized chitosan (Q-CS) and poly(amidoxime) in a cross-linked sulfonated cellulose nanocrystals (S-CNC) network. The cross-linked S-CNC not only can elevate the hydrophilicity to improve the U-adsorption efficiency of AUPM but also can enhance the mechanical strength to form a self-supporting ultrathin membrane (17.21 MPa, 10 μm thickness). More importantly, this AUPM owns a good antibiofouling property, owing to the broad-spectrum antibacterial quaternary ammonium groups of the Q-CS. As a result, within the 1.00 L of low-concentration (100 ppb) U-added pure water (pH ≈ 5) and seawater (pH ≈ 8) for 48 h, 30 mg of AUPM can recover 93.7% U and 91.4% U, respectively. Furthermore, compared with the U-absorption capacity of a blank membrane without the Q-CS, that of AUPM can significantly increase 37.4% reaching from 6.39 to 8.78 mg/g after being in natural seawater for only 25 d. Additionally, this AUPM can still maintain almost constant tensile strength during 10 cycles of adsorption-desorption, which indicates the relatively long-term usability of AUPM. This AUPM will be a promising candidate for highly efficient and large-scale U-recovery from both U-containing waste freshwater/seawater and natural seawater, which will be greatly helpful to deal with the U-pollution and enrich U for the consumption of nuclear power. More importantly, the work will provide a new convenient but universal strategy to fabricate new highly enhanced low-cost U-adsorbents, through the introduction of both an antibacterial property and a high mechanical performance, which will be a good reference for the design of new highly efficient U-adsorbents.

Ni(OH)2 derived Ni-MOF supported on carbon nanowalls for supercapacitors

Metal organic frameworks (MOFs) are expected to be promising pseudocapacitve materials because of their potential redox sites and porous structures. Nevertheless, the conductivity inferiority of MOF strongly decreases their structural advantages, therefore resulting in unsatisfying electrochemical performance. Herein, we propose an efficient strategy to enhance conductivity and thus electrochemical properties, in Ni(OH)₂ is electrochemically deposited on carbon nanowalls as the precursor for oriented MOF. The synthesized vertically oriented MOF sheets show an almost triple high capacitance of 677 F g^-1 than MOF powder of 239 F g^-1 at the current density of 2 A g^-1. Correspondingly, an asymmetric supercapacitor is fabricated, which can deliver a maximum energy density of 20.7 Wh kg^-1 and a maximum power density of 23 200 W kg^-1. These promising results indicate that modulating the conductivity of MOF is the key step to pursuit upgrading electrochemical performance.

Rapid In Situ Polymerization of Polyacrylonitrile/Graphene Oxide Nanocomposites as Precursors for High-Strength Carbon Nanofibers

Graphene oxide (GO) has been widely used as an additive of polyacrylonitrile (PAN)-based carbon nanofibers (CNFs) to optimize its crystal structure and improve the mechanical performances of nanofibers. However, the homogeneous dispersion of GO nanosheets among entangled PAN molecular chains is always challenging, and the poor dispersion of GO severely limits its positive effects on both the structure and performances of CNFs. Considering this issue, this paper provides for the first time an effective solution to achieve rapid and uniform introduction of GO in PAN-based nanofibers via in situ polymerization, and the optimization of the nanofiber structure by GO is systematically studied in three consecutive stages (polymerization, electrospinning, and carbonization) of the production process. During in situ polymerization, PAN is tightly attached on GO nanosheets to form PAN/GO nanocomposites, and this interaction is maintained throughout the spinning process. Not only the arrangement of PAN molecular chains but also the crystal size of the final turbostratic structure of CNFs is considerably improved by the interaction between PAN and GO. Besides, the direct proof that GO nanosheets promote the crystallization and orientation of the nanofiber matrix is presented. As a result, the tensile strength of CNFs is remarkably increased by 2.45 times with 0.5 wt % addition of GO. In summary, this paper provides a method for efficiently introducing nanoscale additives into PAN-based nanofibers and gives insights into the production of high-performance CNFs with the addition of GO.

3D Printing of Lightweight Polyimide Honeycombs with the High Specific Strength and Temperature Resistance

Lightweight structures are often used for applications requiring higher strength-to-weight ratios and lower densities, such as in aircraft, vehicles, and various engine components. Three-dimensional (3D) printing technology has been widely used for lightweight polymer structures because of the superior flexibility, personalized design, and ease of operation offered by it. However, synthesis of lightweight polymeric structures that possess both high specific strength and glass transfer temperature (T_g) remains an elusive goal, because 3D printed polymers with these properties are still very few in the market. For example, 3,3',4,4'-biphenyl tetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA)-type (UPILEX-S type) polyimides show exceptional thermal stability (T_g up to ≈400 °C) and mechanical properties (tensile strength exceeding 500 MPa) and are the first choice if extremely high temperatures of 400 °C or even higher (depending on the duration) are required, which hampers their processing using existing 3D printing techniques. However, their processing using existing 3D printing techniques is hampered due to their thermal resistance. Herein, a 3D printing approach was demonstrated for generating complex lightweight BPDA-PDA polyimide geometries with unprecedented specific strength and thermal resistance. The simple aqueous polymerization reaction of BPDA with water-soluble PDA and triethylamine (TEA) afforded the poly(amic acid) ammonium salt (PAAS) hydrogels. These PAAS solutions showed clear shear thinning and thermo-reversibility, along with high G' gel-state moduli, which ensured self-supporting features and shape fidelity in the gel state. Postprinting thermal treatment transformed the PAAS precursor to BPDA-PDA polyimide (UPILEX-S type). The resulting layer-by-layer deposition onto lightweight polyimide honeycombs in the form of triangular, square, and hexagonal structures showed tailorable mechanical strength, exceptional compressive strength-to-weight ratio (highest up to 0.127 MPa (kg m^-3)^-1), and remarkable thermoresistance (T_g approximately 380 °C). These high-performance 3D printed polyimide honeycombs and unique synthetic techniques with general structures are potentially useful in fields ranging from automotive to aerospace technologies.

Recent Progress on Nanocellulose Aerogels: Preparation, Modification, Composite Fabrication, Applications

The rapid development of modern industry and excessive consumption of petroleum-based polymers have triggered a double crisis presenting a shortage of nonrenewable resources and environmental pollution. However, this has provided an opportunity to stimulate researchers to harness native biobased materials for novel advanced materials and applications. Nanocellulose-based aerogels, using abundant and sustainable cellulose as raw material, present a third-generation of aerogels that combine traditional aerogels with high porosity and large specific surface area, as well as the excellent properties of cellulose itself. Currently, nanocellulose aerogels provide a highly attention-catching platform for a wide range of functional applications in various fields, e.g., adsorption, separation, energy storage, thermal insulation, electromagnetic interference shielding, and biomedical applications. Here, the preparation methods, modification strategies, composite fabrications, and further applications of nanocellulose aerogels are summarized, with additional discussions regarding the prospects and potential challenges in future development.

Convenient ultrasonic preparation of a water stable cluster-based Cadmium(II) coordination material and highly sensitive fluorescent sensing for biomarkers DPA and 5-HT

In recent years, a new type of micro-porous material, namely metal organic framework material, has received more and more attention from many basic and industrial fields because these materials possess unique advantages. In this work, through the powerful sonochemical preparation method, a three-dimensional cluster-based Cd^II-MOFs, {[Cd(abtz)₂(H₂O)₂]·(ClO₄)₂·H₂O}_n (1, abtz = 1-(4-aminobenzyl)-1H-1,2,4-triazole) can be quickly synthesized in the facile ultrasonic method. Powder X-ray diffraction (PXRD) measurement confirms that these bulky samples 1 (synthesized on different ultrasonic powers and ultrasonic time conditions) were pure. In addition, ultrasonic chemical time and irradiation power did not change the structure of composites materials 1. SEM and morphological changes of 1 in the ultrasonic synthesis are also determined. Moreover, 1 exhibits good stability, the structure of 1 can be maintained not just in various solvents, and in aqueous environments with pH values from 2 to 12. Photo-luminescent experiment also reveals that complex 1 has the excellent application prospect as highly sensitive sensing material for the biomarker DPA (2,6-pyridine dicarboxylic acid) and 5-HT (5-hydroxytryptamine) through the photo-luminescence "turn-on" and "turn-off" effect, respectively. Further photo-luminescent measurements also show that different ultrasonic powers and ultrasonic time can effectively induce fluorescent sensing enhancement for biomarkers DPA and 5-HT based on the water stable clustered-based cadmium(II) coordination framework.

Ultralight hybrid silica aerogels derived from supramolecular hydrogels self-assembled from insoluble nano building blocks

Supramolecular hydrogels are a type of hydrogel cross-linked by non-chemical bonds and they have been widely applied in the field of smart systems, sensors, tissue engineering, and controlled drug delivery. Most supramolecular hydrogels are formed by soluble molecules, polymers, and metal ions. In this work, supramolecular hydrogels self-assembled between two insoluble nano building blocks (ISNBBs), graphene oxide (GO) and amino-functionalized silica nanoparticles (SiO₂-NH₂), have been discovered and synthesized. The gelation conditions of the two ISNBBs have been investigated. A step further, ultralight hybrid silica aerogels are obtained by supercritical drying of the physical hydrogels. No visible volume shrinkage is observed, due to the fact that the hydrogel networks are formed by rigid ISNBBs. Thus the hybrid aerogels possess ultralow density (down to 7.5 mg cm^-3), high specific surface areas (178.6 m² g^-1), and extremely high porosity (99.6%). The present work shows an alternative strategy to design and synthesize supramolecular hydrogels and aerogels using predetermined building blocks, together with designable morphology and physical properties for the target aerogels.

Combination of structure-performance and shape-performance relationships for better biphasic release in electrospun Janus fibers

In nature, the combination of composition, structure, and shape determines the matter's functional performance to a large extent. Inspired by which, two electrospun Janus nanofiber formulations were created using side-by-side electrospinning in this work. Tamoxifen citrate (TAM) was used as a model drug and ethyl cellulose (EC) and polyvinylpyrrolidone K60 (PVP) as the polymer carrier matrices. The fibers have linear cylindrical morphologies and distinct Janus structures by scanning electron microscopy. One side of the fibers took a round shape, while the other was crescent-shaped. The drug was present in both polymer matrices in the form of amorphous solid dispersions, owing to strong intermolecular interactions between drug and polymer. In vitro dissolution tests demonstrated that both sets of fibers could provide biphasic drug release due to the difference in solubility of PVP and EC. The different shape of TAM-EC and TAM-PVP side of the Janus structure resulted in a considerable variation in the drug release profiles. The Janus structure with crescent TAM-PVP side and round TAM-EC side gave a more rapid burst release in the first phase of release, and slower sustained release in the second phase. This work thus reports a new strategy for systematically developing advanced functional nanomaterials based on both shape- and structure-performance relationships.

Supramolecularly Poly(amidoxime)-Loaded Macroporous Resin for Fast Uranium Recovery from Seawater and Uranium-Containing Wastewater

Uranium is an extremely abundant resource in seawater that could supply nuclear fuel for over the long-term, but it is tremendously difficult to extract. Here, a new supramolecular poly(amidoxime) (PAO)-loaded macroporous resin (PLMR) adsorbent has been explored for highly efficient uranium adsorption. Through simply immersing the macroporous resin in the PAO solution, PAOs can be firmly loaded on the surface of the nanopores mainly by hydrophobic interaction, to achieve the as-prepared PLMR. Unlike existing amidoxime-based adsorbents containing many inner minimally effective PAOs, almost all the PAOs of PLMR have high uranium adsorption efficiency because they can form a PAO-layer on the nanopores with molecular-level thickness and ultrahigh specific surface area. As a result, this PLMR has highly efficient uranium adsorbing performance. The uranium adsorption capacity of the PLMR was 157 mg/g (the U_PAO in the PLMR was 1039 mg/g), in 32 ppm uranium-spiked seawater for 120 h. Additionally, uranium in 1.0 L 100 ppb U-spiked both water and seawater can be removed quickly and the recovery efficiency can reach 91.1 ± 1.7% and 86.5 ± 1.9%, respectively, after being filtered by a column filled with 200 mg PLMR at 300 mL/min for 24 h. More importantly, after filtering 200 T natural seawater with 200 g PLMR for only 10 days, the uranium-uptake amount of the PLMR reached 2.14 ± 0.21 mg/g, and its average uranium adsorption speed reached 0.214 mg/(g·day) which is very fast among reported amidoxime-based adsorbents. This new adsorbent has great potential to quickly and massively recover uranium from seawater and uranium-containing wastewater. Most importantly, this work will provide a simple but general strategy to greatly enhance the uranium adsorption efficiency of amidoxime-functionalized adsorbents with ultrahigh specific surface area via supramolecular interaction, and even inspire the exploration of other adsorbents.

Novel silver(i) cluster-based coordination polymers as efficient luminescent thermometers

Two original Ag-based clusters with a multidentate N-containing organic linker have been constructed featuring temperature-dependent luminescence behavior.

A water-stable zinc(ii)–organic framework as an “on–off–on” fluorescent sensor for detection of Fe3+ and reduced glutathione

A zinc(ii) metal–organic framework exhibits fluorescence on–off–on behaviour for Fe³⁺ and reduced glutathione in PBS solution and in real samples.

Preparation of high-strength polyimide membranes capped by ionic liquids

In this study, we firstly used 1-carboxyethyl-3-methylimidazolium ionic liquid as a capping agent to terminate a binary linear polyimide containing different groups such as ether bonds, carbonyl groups, and fluorine, and prepared six kinds of polyimides capped with ionic liquids (IL-PI). The mechanical properties of the polyimide membranes capped with ionic liquids were higher than those of the uncapped polyimide membranes. The elastic modulus of polyimide membrane from 1,3-bis (4-aminophenoxy) benzene (BPDA) and 3,3′4,4′-benzophenone tetracarboxydianhydride (BTDA) by using ionic liquid as the end capping agent (IL-BPDA-BTDA) was 2012 MPa, which is about 70 times higher than that without the end capping agent. In a TG test, all polyimides capped by ionic liquids showed good thermal properties. The residual amount of the polyimides was more than 40% at 1000 °C, which was higher than the other uncapped polyimides. In conclusion, polyimide membranes with high temperature resistance and high mechanical strength were prepared through an ionic liquid termination method.

A review of smart electrospun fibers toward textiles

Electrospinning as a versatile technology has attracted a large amount of attention in the past few decades due to the facile way to produce micro- and nano-scale fibers featuring flexibility, large specific surface area and high porosity. Stimuli-responsive polymers are a class of smart materials that are capable of sensing surround environment and interacting with them. Therefore, the combination of electrospinning and smart materials could have a great deal of benefits over the development of smart fibers. In this review, it offers a comprehensive understanding of smart electrospun fibers toward textile applications. Firstly, the definition of smart fibers and the differences between interactive fibers and passive interactive fibers are briefly introduced. Then some interactive fibers made from temperature-, pH-, light-, electric field/electricity-, magnetic field-, multi-responsive polymers, as well as some polymers featuring piezoelectric and triboelectric effect which are suitable flexible electrics, are emphasized with their applications in the form of electrospun fibers. Afterwards, some passive and hybrid smart electrospun fibers are introduced. Finally, associated challenges and perspectives are summarized and discussed.

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Understanding of passive smart electrospun fibers and interactive smart electrospun fibers.

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The recent progress in flexible electronics from electrospun fibers.

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The recent progress in stimuli-responsive polymers applied in interactive smart electrospun fibers.

Uniform-thickness electrospun nanofiber mat production system based on real-time thickness measurement

Electrospinning is a simple versatile process used to produce nanofibers and collect them as a nanofiber mat. However, due to bending instability, electrospinning often produces a nanofiber mat with non-uniform mat thickness. In this study, we developed a uniform-thickness electrospun nanofiber mat (UTEN) production system with a movable collector based on real-time thickness measurement and thickness feedback control. This system is compatible with a collector with void regions such as a mesh-type collector, two-parallel-metal-plate collector, and ring-type collector, which facilitates the measurement of light transmittance across the produced nanofiber mat during electrospinning. A real-time measurement system was developed to measure light transmittance and convert it to the thickness of the nanofiber mat in real time using the Beer-Lambert law. Thickness feedback control was achieved by repeating the following sequences: (1) finding an optimal position of the movable collector based on the measured thickness of the nanofiber mat, (2) shifting the collector to an optimal position, and (3) performing electrospinning for a given time step. We found that the suggested thickness feedback control algorithm could significantly decrease the non-uniformity of the nanofiber mat by reducing the standard deviation by more than 8 and 3 times for the numerical simulation and experiments, respectively, when compared with the conventional electrospinning. As a pioneering research, this study will contribute to the development of an electrospinning system to produce robust and reliable nanofiber mats in many research and industrial fields such as biomedicine, environment, and energy.

Selective and simultaneous sensing of ascorbic acid, dopamine and uric acid based on nitrogen-doped mesoporous carbon

Development of novel sensing nanostructures for facile, economical and fast applications has attracted more and more interest. Herein, a nitrogen-doped mesoporous carbon (NMC) was synthesized by pyrolyzing a mixture of melamine and carbon black at a low-temperature (600 °C) and exploited for the simultaneous sensing of ascorbic acid (AA), dopamine (DA) and uric acid (UA). The as-made NMC exhibits a rougher surface and smaller size than carbon black. Such a one-pot method is very versatile, quick and inexpensive, easy to handle (solvent-, catalyst-, and template-free) and scalable. The oxidation potentials of the NMC/GCE negatively shift and the current responses are enhanced greatly towards the oxidation of AA, DA and UA thanks to the large surface area, mesoporous structure and N-doped active sites. The peak to peak potential separations are 258 and 410 mV for AA-DA and AA-UA. The linear ranges of AA, DA and UA are 5-4500 μM, 0.005-35 μM and 0.5-3500 μM, respectively, and their detection limits are 0.15 μM (AA), 1.6 nM (DA) and 0.15 μM (UA). Meanwhile, the NMC/GCE exhibits satisfactory stability and anti-interference ability. These results show that NMC could be a promising candidate material for electrochemical sensor construction.

Structural design toward functional materials by electrospinning: A review

Electrospinning as one of the most versatile technologies have attracted a lot of scientists’ interests in past decades due to its great diversity of fabricating nanofibers featuring high aspect ratio, large specific surface area, flexibility, structural abundance, and surface functionality. Remarkable progress has been made in terms of the versatile structures of electrospun fibers and great functionalities to enable a broad spectrum of applications. In this article, the electrospun fibers with different structures and their applications are reviewed. First, several kinds of electrospun fibers with different structures are presented. Then the applications of various structural electrospun fibers in different fields, including catalysis, drug release, batteries, and supercapacitors, are reviewed. Finally, the application prospect and main challenges of electrospun fibers are discussed. We hope that this review will provide readers with a comprehensive understanding of the structural design and applications of electrospun fibers in different fields.

Solvent Vapor Strengthened Polyimide Nanofiber-Based Aerogels with High Resilience and Controllable Porous Structure

Owing to the hierarchically three-dimensional (3D) network, ultralow density, and high porosity, nanofiber-based aerogels (NFAs) have drawn great attention recently. However, precise control of the porous structure and mechanical properties of NFAs, which have been proved to be extremely essential to the applications, still remains a major challenge. Herein, electrospun polyimide (PI) nanofibers were utilized as building blocks to construct NFAs through the solid-templating technique. The porous structure of PI nanofiber-based aerogels (PI-NFAs) could be adjusted by changing the processing parameters. By further welding the adjacent nanofibers at the contact sites with solvent vapor, high-resilience PI-NFAs were successfully prepared with comparable or higher recoverable, under compression, folding and torsion relative to other NFAs. The welded PI-NFAs showed ultralow density (minimum of 0.96 mg/cm³), high porosity (maximum of 99.93%), and tunable hierarchical structure. Therefore, this study brought a new perspective on the simple preparation of high-resilience nanofiber-based aerogels with tunable porous structures.

An "on-off-on" selective fluorescent probe based on nitrogen and sulfur co-doped carbon dots for detecting Cu2+ and GSH in living cells

The abnormal level of Cu²⁺ or GSH can cause variety of neurodegenerative diseases in humans. Thus, the selective and sensitive detection of Cu²⁺ and GSH has inspired intensive research efforts in biological sample analysis fields. Herein, an "on-off-on" fluorescent probe based on nitrogen and sulfur co-doped carbon dots (N,S-CDs) has been successfully prepared for the detection of Cu²⁺ and GSH. The "turn-off" process of fluorescence in the presence of Cu²⁺ ions was induced by forming a non-luminescent ground state complex due to the interaction between surface groups of the probe and Cu²⁺ ions. Moreover, the strong coordination between GSH and Cu²⁺ could destroy the structure of the complex and restore the fluorescence to "turn-on". This fluorescent probe had excellent selectivity and high sensitivity toward Cu²⁺ and GSH with the limits of detection (LODs) of 38 nM and 41 nM. More importantly, the as-prepared N,S-CDs served as an efficient fluorescent probe for not only detecting Cu²⁺ ions in lake water and tap water, and GSH in BSA solution, but also sensing Cu²⁺ and GSH in living cells. Therefore, these N,S-CDs could be considered as a promising fluorescence probe candidate for environmental monitoring and biological imaging.

Fabrication of flexible SiO2 nanofibrous yarn via a conjugate electrospinning process

Nowadays, different kinds of polymers, including ceramics, are electrospun into fibrous materials with different structures by electrospinning. Generally, the as-spun ceramic fibers are randomly oriented membranes and brittle without flexibility. Here, we report the fabrication of flexible SiO2 electrospun yarns using poly(vinyl alcohol) (PVA) as a template through a conjugate electrospinning process and calcination. It was found that the calcined as-spun fibers and yarns are obviously thinned with PVA component removal. Fourier transform infrared spectroscopy and energy-dispersive spectroscopy examinations suggested that the obtained yarn after calcination was SiO2 yarn. The SiO2 yarn showed good flexibility without cracking after 180° bending. The flexible ceramic yarn may have potential application in functional textiles.

Reaction-Spun Transparent Silica Aerogel Fibers

Aerogel fibers, the simultaneous embodiment of aerogel 3D network and fibrous geometry, have shown great advantages over natural and synthetic fibers in thermal insulation. However, as a fast gelation to ensure aerogel fiber spinning generally induces rapid local clustering of precursor particles (i.e., phase separation) and unavoidably results in nontransparency and nonuniformity in the gel state, a severe challenge remains in remedying the spinning to make transparent aerogel fibers come true. Herein, we report a reaction spinning toward highly porous silica aerogel fibers, where the Brownian motion (i.e., diffusion) of colloidal particles is hampered during spinning to allow the maintaining of the fiber shape, while a rapid gelation reaction is activated by concentrated ammonia to solidify the fiber. The aggregation degree of the primary particles can be precisely controlled by pH-dependent hydrolyzation, and thus, the final aerogel fiber can be either transparent or opaque, as dominated by Rayleigh or Mie scattering. The resulting transparent silica aerogel fibers with low density, high specific surface area, and flexibility can inherit advanced features including excellent thermal insulation, wide temperature stability, and optional hydrophobic functionalization and, thus, be suitable for wearable applications.

Preparation of PI/PTFE-PAI Composite Nanofiber Aerogels with Hierarchical Structure and High-Filtration Efficiency

Electrospun nanofiber, showing large specific area and high porosity, has attracted much attention across various fields, especially in the field of air filtration. The small diameter contributes to the construction of filters with high-filtration efficiency for fine particulate matter (PM), however, along with an increase in air resistance. Herein, composited nanofiber aerogels (NAs), a truly three-dimensional (3D) derivative of the densely compacted electrospun mat, were constructed with the blocks of polytetrafluoroethylene-polyamideimide (PTFE-PAI) composite nanofiber and polyimide (PI) nanofiber. PI/PTFE-PAI NAs with hierarchically porous architecture and excellent mechanical properties have been obtained by thermally induced crosslink bonding. Results indicated that sintering at 400 °C for 30 min could complete the decomposition of polyethylene (PEO) and imidization of polyamic acid (PAA) into PI, as well as generate sufficient mechanical bonding between adjacent nanofibers in the NAs without extra additive. The well-prepared PI/PTFE-PAI NAs could withstand high temperature up to 500 °C. In addition, the filtration tests illustrated that the composite NAs had an excellent performance in PM filtration. More importantly, the filtration behavior could be adjusted to meet the requirements of various applications. The excellent thermal stability and high-filtration efficiency indicated its great potential in the field of high-temperature air filtration.