Polymeric Fibers with High Strength and High Toughness at Extreme Temperatures.

Developing strong and simultaneously tough polymeric materials with excellent thermal stability and mechanical performance even under extreme temperatures is truly a challenge. In a disruptive progress, continuous polymeric yarns are developed with a combination of high tensile strength of (1145 ± 44) MPa and ultrahigh toughness of (350 ± 24) J g-1 and high thermomechanical properties from -196 to 200 °C. The comprehensive thermomechanical performance of this yarn surpasses that of previously developed polymeric materials and dragline spider silks. The results demonstrate that the molecular structure of polyimide (PI) with the incorporation of flexible-rigid macromolecular, hierarchically spiral-oriented fibers, and high glass transition temperature (248 °C) are keys for the yarn's notable comprehensive performance in thermomechanical properties. The materials are ideal for technical components exposed to high thermomechanical loadings, such as those encountered in spacecraft or automotive engineering for safety-critical applications.

Enhanced cycling stability of Li-sulfur battery composites by low pressure penetration of PEDOT:PSS coating.

A lithium sulfur composite electrode (SCPV) is prepared by in situ permeation of poly (3,4-dioxyethiophene):poly(styrene sulfonate) (PEDOT:PSS) with a thickness of about 10 nm onto the surface of a SC (sulfur and carbon nanotubes) electrode via a low pressure (3.3 kPa) method. The SCPV electrode exhibits a discharge capacity of 1320.0 mA h g-1, which is higher than that of the SC electrode (1265.8 mA h g-1) at 0.1C; furthermore, it exhibits a discharge capacity of 604.9 mA h g-1, which is almost twice that of the SC electrode (306.8 mA h g-1) at 2C, and it is due to the fact that PEDOT:PSS gel polymers store large amounts of electrolytes and have excellent electronic and ionic conductivities. However, the discharge capacity of a SCPV cathode remains at 91.87% after 200 cycles at 0.5C, which is more than twice that of the SC cathode (44.70%); this superior cycling stability is mainly due to the in situ fixation of PEDOT:PSS inside the SC electrode, which inhibits the shuttle effect and volume change during the cycling process, thus improving the cycling stability.

In Situ Fabrication of High Dielectric Constant Composite Films with Good Mechanical and Thermal Properties by Controlled Reduction.

As a common two-dimensional carbon material, graphene has been widely doped into polymers to prepare high-performance dielectric materials. However, the shortcomings of graphene, such as large specific surface area and poor dispersion, limit its further application. Therefore, in this work, to solve the problem regarding the uniform dispersion of graphene in the matrix, in situ polymerization was used to prepare graphene/polyimide films, in which 1,4-diiodobutane was used as a reduction agent to prevent the aggregation of graphene oxide (GO) during imidization. High dielectric constant composite films were obtained by adjusting the ratio of 1,4-diiodobutane in GO. The results show that the resulting graphene/polyimide composite film possessed a dielectric constant of up to 197.5, which was more than 58 times higher than that of the polyimide (PI) film. Furthermore, compared to the pure PI film, the composite films showed better thermal stability and mechanical properties. Thermal performance tests showed that the 1,4-diiodobutane added during the preparation of the composite film was thermally decomposed, and there was no residue. We believe our preparation method can be extended to other high dielectric composite films, which will facilitate their further development and application in high power density energy storage materials.

Thermal, Mechanical and Dielectric Properties of Polyimide Composite Films by In-Situ Reduction of Fluorinated Graphene.

Materials with outstanding mechanical properties and excellent dielectric properties are increasingly favored in the microelectronics industry. The application of polyimide (PI) in the field of microelectronics is limited because of the fact that PI with excellent mechanical properties does not have special features in the dielectric properties. In this work, PI composite films with high dielectric properties and excellent mechanical properties are fabricated by in-situ reduction of fluorinated graphene (FG) in polyamide acid (PAA) composites. The dielectric permittivity of pure PI is 3.47 and the maximum energy storage density is 0.664 J/cm3 at 100 Hz, while the dielectric permittivity of the PI composite films reaches 235.74 under the same conditions, a 68-times increase compared to the pure PI, and the maximum energy storage density is 5.651, a 9-times increase compared to the pure PI films. This method not only solves the problem of the aggregation of the filler particles in the PI matrix and maintains the intrinsic excellent mechanical properties of the PI, but also significantly improves the dielectric properties of the PI.

Ultralight Heat-Insulating, Electrically Conductive Carbon Fibrous Sponges for Wearable Mechanosensing Devices with Advanced Warming Function.

Ultralight highly porous sponges are attractive for electronic devices due to superelasticity, outstanding resilience, and thermal insulation. However, fabricating an ultralight conductive sponge with low thermal conductivity, mechanical flexibility, and piezoresistivity, as well as adjustable heating behavior, is still a challenge. Here, an ultralight carbon nanofibrous sponge fabricated by pyrolyzing a graphene oxide coated polyimide sponge is reported. The resulting carbon sponge demonstrates a high electrical conductivity of 0.03-4.72 S m-1 and a low thermal conductivity of 0.027-0.038 W m-1 K-1 (20 °C, in ambient air), as well as a low density to ∼6 mg cm-3. Additionally, the sponge exhibits mechanical flexibility, stability, excellent piezoresistivity, and an adjustable heating behavior. Hence, it could be utilized as a sensing device, including thermal management, making them promising for use in smart sportswear, human-machine interfaces, and wearable healthcare devices.

Synthesis of Dihydrochromeno[2,3-b]indoles via an Fe(OTf)3-Catalyzed Cascade Reaction.

A tandem cyclization between 2-(2-aminophenyl)acetonitriles and 2-(hydroxy(aryl)methyl)phenols for the preparation of dihydrochromeno[2,3-b]indole derivatives was successfully developed. The transformation proceeded smoothly in the presence of a catalytic environmentally benign iron salt, and various multisubstituted dihydrochromeno[2,3-b]indoles were synthesized in moderate to high yields.

High Cycling Stability of the LiNi0.8 Co0.1 Mn0.1 O2 Cathode via Surface Modification with Polyimide/Multi-Walled Carbon Nanotubes Composite Coating.

The Ni-rich LiNi0.8 Co0.10 Mn0.1 O2 (NCM811) cathode coated by combining with multi-walled carbon nanotubes (MWCNTs) and polyimide (PI) produces a PI3-NCM811 cathode, which markedly improves cycling stability and suppresses secondary crystal cracking. The initial discharge capacity of the PI3-NCM811 cathode is 199.6 mAh g-1 between 2.8 and 4.3 V at 0.1 C @ 25 °C, which is slightly lower than that of NCM811 (201.1 mAh g-1 ). The PI3-NCM811 and NCM811 cathodes keep 90.6% and 64.8% of their initial discharge capacity at 1 C between 2.8 and 4.3 V after 500 cycles, respectively. Furthermore, the difference (21.1%) in capacity retention rate between PI3-NCM811 and NCM811 under the condition of 2.8-4.5 V became smaller compared with the difference (25.8%) under the condition of 2.8-4.3 V. This better cyclic stability is mainly attributed to the toughness and elasticity of PI, which inhibits the secondary cracking, maintains the structural integrity of the cathode particles, and protects the particles from electrolyte damage during long-term cycling.

Nitrogen, sulfur co-doped hierarchical carbon encapsulated in graphene with "sphere-in-layer" interconnection for high-performance supercapacitor.

Rational design of electrode with hierarchical charge-transfer structure and good electronic conductivity is important to achieve high specific capacitance and energy density for supercapacitor, but it still remains a challenge. Herein, a nitrogen, sulfur co-doped pollen-derived carbon/graphene (PCG) composite with interconnected "sphere-in-layer" structure was fabricated, in which hierarchically pollen-derived carbon microspheres can serve as "porous spacers" to prevent the agglomeration of graphene nanosheets. The optimized PCG composite prepared with 0.5 wt% of graphene oxide (PCG-0.5) exhibited high specific capacitance (420Fg-1 at 1Ag-1), rate performance (280Fg-1 at 20Ag-1), and excellent cycling stability with 94% of capacitance retention after 10,000 cycles. The symmetrical device delivered a remarkable energy density of 31.3Whkg-1 in neutral medium. Moreover, density functional theory calculation revealed that PCG electrode possessed the accelerated charge transfer and enhanced electronic conductivity, thus ensuring a remarkable electrochemical performance. This work may afford an effective strategy for the development of biomass-derived carbon electrodes with novel charge-transfer structure toward supercapacitor applications.

Surface Modification of the LiNi0.8Co0.1Mn0.1O2 Cathode Material by Coating with FePO4 with a Yolk-Shell Structure for Improved Electrochemical Performance.

Coating with FePO4 with the size of 20-30 nm on the surface of a LiNi0.8Co0.10Mn0.1O2 (NCM811) cathode produces an LFP3@NCM811 cathode via a sol-gel method, which markedly reduces secondary crystal cracking. A stable particle structure greatly improves the cycling stability of the LFP3@NCM811cathode, which retains 97% of its initial discharge capacity compared to NCM811 (78%) after 100 cycles at 2.7-4.5 V. Furthermore, it retains 86 and 63% of its initial discharge capacity after 400 cycles for LFP3@NCM811 and NCM811, respectively. The initial discharge capacity of the LFP3@NCM811 cathode is 218.8 mAh g-1 at 0.1 C, and the discharge capacity of the LFP3@NCM811 cathode is achieved to be 151.4 mAh g-1 at 5 C, which is 15 mAh g-1 higher than that of the NCM811 cathode. These are due to the reduction of cation mixing for a certain amount of Fe2+/Fe3+ or PO43- doped into the NCM811 surface, and the yolk-shell structure formed by coating with FePO4 helps improve the electronic conductivity and accelerate the Li+ transport. The cycling stability is mainly due to the secondary cleavage inhibition, which maintains the structural integrity of the cathode particles during the long cycle process and protects the inside of the particle from harmful electrolytes.

Ultralight, Structurally Stable Electrospun Sponges with Tailored Hydrophilicity as a Novel Material Platform.

Sponges based on short electrospun fibers have received significant attention due to their ultrahigh porosity, lightweight, and multifunctional characteristics. In particular, polyimide (PI) sponges have been researched due to their exceptional mechanical properties and thermal stability. Nevertheless, a number of sponges, including PI, are usually hydrophobic and synthesized in toxic, nonwater solvents (e.g., 1,4-dioxane). Conversely, hydrophilic sponges disintegrate upon contact with water. Here, we suggest a new strategy to fabricate PI sponges in water by introducing a suitable surfactant, sodium dodecylbenzenesulfonate (SDBS) (sPI sponges). With less than 1 wt % of SDBS with respect to PI short fibers, they can be homogeneously dispersed in water and mixed well with poly(amic acid) (PAA) solution. The synthesized sponge, depending on the concentration of SDBS, showed hydrophilic properties and substantial water uptake above 5000%. The hydrophilic properties of the sponges, which are not common, and the preparation from aqueous solution introduce new research opportunities. Such hydrophilic sponges are particularly special because they do not swell in contact with water, which makes them dimensionally stable. The methods presented here can serve as a milestone for the future development of various kinds of hydrophilic sponges applied for various applications, ranging from tissue engineering to oil/water separation.

Carbonization: A feasible route for reutilization of plastic wastes.

Plastics not only bring convenience and color to human life, but also bring endless troubles and disaster to our environment. Reutilization of plastic wastes is in favor of energy conservation and emission reduction, thereby is a significant pathway of plastic wastes disposal. Carbonization is an effective way of converting polymer precursors to valuable carbon materials for use in fields of energy conversion and storage, environmental protection and restoration. Here, we present a systematic multi-perspective overview of carbonization as a feasible route of reutilization of plastic wastes. A brief summary of conventional routes for plastic wastes is followed by a brief introduction of carbonization for converting plastics to carbon materials. Special emphasis is paid on the carbonization pathways and mechanisms of common plastics. Finally, the feasibility, application prospect and challenge of carbonization as one method of reutilization of plastic wastes are proposed. By presenting a consolidated information source on different carbonization mechanisms, this review provides a valuable guideline for reutilization of plastic wastes by carbonization.

High strength in combination with high toughness in robust and sustainable polymeric materials.

In materials science, there is an intrinsic conflict between high strength and high toughness, which can be resolved for different materials only through the use of innovative design principles. Advanced materials must be highly resistant to both deformation and fracture. We overcome this conflict in man-made polymer fibers and show multifibrillar polyacrylonitrile yarn with a toughness of 137 ± 21 joules per gram in combination with a tensile strength of 1236 ± 40 megapascals. The nearly perfect uniaxial orientation of the fibrils, annealing under tension in the presence of linking molecules, is essential for the yarn's notable mechanical properties. This underlying principle can be used to create similar strong and tough fibers from other commodity polymers in the future and can be used in a variety of applications in areas such as biomedicine, satellite technology, textiles, aircrafts, and automobiles.

A Sensitive Pyrimethanil Sensor Based on Electrospun TiC/C Film.

Titanium carbide (TiC) is a very significant transition metal carbide that displays excellent stability and electrical conductivity. The electrocatalytic activity of TiC is similar to noble metals but is much less expensive. Herein, carbon nanofibers (CNFs)-supported TiC nanoparticles (NPs) film (TiC/C) is prepared by electrospinning and carbothermal processes. Well-dispersed TiC NPs are embedded tightly into the CNFs frameworks. The electrochemical oxidation of pyrimethanil (PMT) at the TiC/C-modified electrode displays enhanced redox properties, and the electrode surface is controlled simultaneously both by diffusion and adsorption processes. When TiC/C is applied for PMT determination, the as-fabricated sensor shows good sensing performance, displaying a wide linear range (0.1⁻600 µM, R² = 0.998), low detection limit (33 nM, S/N = 3), and good reproducibility with satisfied anti-interference ability. In addition, TiC/C shows long-term stability and good application in natural samples. The facile synthetic method with good sensing performance makes TiC/C promising as novel electrode materials to fabricate efficient sensors.

Gradient-Structured Nonflammable Flexible Polymer Membranes.

Herein, we report the formation and properties of a rare example of high-performance composite membranes from polybisbenzimidazobenzophenanthroline-dione (BBB) that do not sustain a flame or burn with smoke nor show melt dripping. In addition, this material possesses a low density and very high thermal stability (char yield as high as 80-94%), strength, and flexibility. Such membranes are highly desirable for battery separators, protective clothing, construction, and automobiles. Because BBB is an insoluble and infusible polymer, the composite membranes were made using a bottom-up vacuum-assisted self-assembly method with an aqueous dispersion of short BBB fibers and Hec. The use of water as the solvent, upscalability, and excellent flame retardancy in combination with low density, flexibility, and low thermal conductivity of the composite membranes make the preparation method and membranes highly promising for future use in real applications.

Investigating the draw ratio and velocity of an electrically charged liquid jet during electrospinning.

The investigation of the draw ratio and velocity of an electrospinning polymer solution jet is of great interest for understanding the formation of nanofibers. During the electrospinning process, the charged polymer solution jets were stretched by electric force, resulting in the formation of ultrathin fibers. In this study, theoretical deduction and experimental calculation were applied to evaluate the velocities and draw ratios of the charged jets at different electrospinning stages. Depending on the diameter of the charged jets at different electrospinning stages, the velocities and draw ratios of the charged jets were calculated with values far lower than the data in a previous report. The theoretical calculation was compared with experimental data using polyamic acid as a model polymer for electrospinning. The results indicated that during electrospinning, as the collecting distance was increased from 0 to 30 cm, the diameter of the electrospinning jet decreased from 18 800 nm to a constant value of around 245 nm, the solvent in the jet decreased from 96.50 wt% to 25.45 wt%, and the density of the jet increased from 0.9504 to 1.0995 g cm-3. These parameters led to the draw ratio and velocity of the jet experiencing first an increase and then a decrease in the value, and the highest draw ratio and velocity were 869 and 867 m s-1, respectively, which are quite different from the data in previous reports.

Molecular orientation in aligned electrospun polyimide nanofibers by polarized FT-IR spectroscopy.

Quantitative explanation on the improved mechanical properties of aligned electrospun polyimide (PI) nanofibers as the increased imidization temperatures is highly required. In this work, polarized FT-IR spectroscopy is applied to solve this problem. Based on the polarized FT-IR spectroscopy and the molecular model in the fibers, the length of the repeat unit of PI molecule, the angle between the fiber axis and the symmetric stretching direction of carbonyl group on the imide ring, and the angle between the PI molecular axis and fiber axis are all investigated. The Mark-Howink equation is used to calculate the number-average molar mass of PI molecules. The orientation states of PI molecules in the electrospun nanofibers are studied from the number-average molar mass of PI molecules and the average fiber diameter. Quantitative analysis of the orientation factor of PI molecules in the electrospun nanofibers is performed by polarized FT-IR spectroscopy.

Dual-Bioinspired Design for Constructing Membranes with Superhydrophobicity for Direct Contact Membrane Distillation.

Water flux and durability are the two critical parameters that are closely associated with the practical application of membrane distillation (MD). Herein, we report a facile approach to fabricate superhydrophobic polyimide nanofibrous membranes (PI NFMs) with hierarchical structures, interconnected pores, and high porosity, which was derived from the electrospinning, dual-bioinspired design, and fluorination processes. Bioinspired adhesive based on polydopamine /polyethylenimine (PDA/PEI) composite was first linked onto membrane substrates and then assembled lotus leaf hierarchical structure by binding the negatively charged silica nanoparticles (SiO2 NPs) via electrostatic attraction. The resultant superhydrophobic PI NFMs exhibit a water contact angle of 152°, robust hot water resistance of 85 °C, and high water entry pressure of 42 kPa. Moreover, the membrane with omniphobicity presents high water flux over 31 L m-2 h-1 and high salts rejection of ∼100% as well as robust durability for treating high salinity wastewater containing typical low surface tension and dissolved contaminants (Δ T = 40 °C). Significantly, the novel dual-bioinspired method can be used as a universal tool to modify various materials with hierarchical structures, which is expected to provide more effective alternative membranes for MD and even for other selective wetting separation fields.

One-Step Preparation of Highly Hydrophobic and Oleophilic Melamine Sponges via Metal-Ion-Induced Wettability Transition.

Hydrophobic and oleophilic absorbent materials have received wide attention in recent years for potential applications in pollutant removal from accidental spills of oil or organic chemicals. In this work, we report a metal-ion-induced hydrophobic melamine sponge (MII-HMS) prepared by a one-step solution immersion process. The commercial melamine sponge (intrinsically superhydrophilic with a water contact angle of ∼0°) is immersed in an aqueous solution of transition metal ions (e.g., FeCl3, Fe(NO3)3, Zn(NO3)2, Ni(NO3)2, and Co(NO3)2) for a short period, followed by drying. This simple process renders the transition of the superhydrophilic melamine sponge to become highly hydrophobic (a water contact angle of ∼130°). Results from X-ray photoelectron spectroscopy and infrared spectroscopy suggest that the unprecedented transition is likely due to the formation of metal complexes during immersion. The MII-HMS is also oleophilic, exhibiting excellent oil absorption capabilities, ∼71-157 times of its weight, for a wide range of oils and organic solvents. Our work offers a simple, scalable, and economical approach to fabricate highly efficient absorbent materials for potential applications in oil spill recovery and environmental remediation.

Flexible and conductive titanium carbide-carbon nanofibers for the simultaneous determination of ascorbic acid, dopamine and uric acid.

The development of novel materials for facile, cost-effective and quick practical application is a demanding research interest in electroanalytical chemistry. Titanium carbide (TiC), as one of the most important transition metal carbides, exhibits good chemical stability and electrical conductivity, and its electrocatalytic activity resembles that of metals, but is much cheaper. In this work, TiC nanoparticle (NP) loaded carbon nanofiber (CNF) films (TCNFs) are synthesized using an electrospinning and carbothermal technique, which facilely maintains their structural integrity with robust adhesion. Uniform TiC NPs are firmly embedded in the surface of CNFs, which integrates the large surface area and unique 3D, porous network structure of CNFs with the good conductivity and excellent electrocatalytic activity of TiC NPs. Simultaneous electrochemical sensing of ascorbic acid (AA), dopamine (DA) and uric acid (UA) at TCNFs displays excellent peak current signals with well-defined peak potentials. The linear ranges are 0.001-1.5 mM, 0.05-160 µM and 0.001-0.875 mM for AA, DA and UA, and the corresponding detection limits are 0.3 µM, 20 nM and 0.3 µM, respectively. In addition, TCNFs show long-term sensing stability and potential applications in real samples, and behave as good anti-interference agents towards KNO3, ZnSO4, glucose, etc. Most importantly, unlike some common carbon-based electrochemical sensor systems, an adsorption-less response is observed for the test analytes at the TCNF electrode. TCNFs show interesting potential as candidates for the construction of electrochemical sensors.

Nanofibers with diameter below one nanometer from electrospinning.

Sub-nanometer materials have received wide attention due to their unique properties in recent years. Most studies focus on the preparation and properties investigation of the inorganic sub-nanometer materials, while there are few reports on organic especially polymeric sub-nanometer materials such as sub-nanometer fiber due to the obstacles with respect to fabricating such small nanofibers. In this work we prepare PAA nanofibers with diameters ranging from hundreds of nanometers down to sub-nanometer via electrospinning from a polyamic acid (PAA) with ultrahigh molecular weight. The morphologies and size of the electrospun ultrathin nanofibers are characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). AFM images combined with theoretic calculations show that sub-nanometer fiber of approximate 0.17-0.63 nm only containing one molecular chain was generated via electrospinning from ultra-dilute PAA solutions for the first time. These quite small sub-nanometer fibers would open a new area of electrospinning and provide further explorations on the production and application of electrospun sub-nanometer fibers with single molecular chains.