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Polyamide-imides (PAIs) are highly desired in many applications because of their superior thermal and mechanical properties. In this work, PAI was prepared from an amide-containing diamine and dianhydride by polycondensation and thermal treatment. Both PAI films and aligned electrospun nanofibers (ANFs) were fabricated. FT-IR was used to determine the structure formation of PAI at different annealing temperatures. DSC and TGA were used to evaluate the thermal properties of PAI, while tensile test was applied to evaluate the mechanical properties of PAI films and ANFs. The results indicated that the PAI possessed both outstanding thermal stability and mechanical properties, which provide opportunities for applications in gas separation, high temperature filtration, reinforcement, etc. [ABSTRACT FROM AUTHOR]

High mechanical performance carbon nanofibers are highly required for the carbon nanofiber-reinforced composites, and it is necessary to develop novel precursors for the preparation of carbon nanofibers. In this work, blends of poly(acrylonitrile-butyl acrylate mono-butyl itaconate) (co-PAN) and polyamic acid (PAA) were electrospun into aligned nanofibers and the nanofibers were converted to carbon nanofibers by thermal imidization, pre-oxidation and high-temperature carbonization. FT-IR spectroscopy was applied to monitor the chemical structures of the nanofibers before and after pre-oxidation. Tensile tests were used to characterize the mechanical properties of electrospun carbon nanofibers (ECNFs). The microstructures of ECNFs were investigated by high-resolution TEM and Raman spectroscopy. The results indicated that the ECNFs derived from blend of co-PAN/PAA with molar ratio of 6/4 and with carbonization temperature of 1400 °C possessed the highest tensile strength of 1212 MPa, which could be attributed to the ordered graphitic structures in ECNFs. [ABSTRACT FROM AUTHOR]

Ultralight cellular sponges offer a unique set of properties. We show here that solvent uptake by these sponges results in new gel-like materials, which we term spongy gels. The appearance of the spongy gels is very similar to classic organogels. Usually, organogels are formed by a bottom-up process. In contrast, the spongy gels are formed by a top-down approach that offers numerous advantages for the design of their properties, reproducibility, and stability. The sponges themselves represent the scaffold of a gel that could be filled with a solvent, and thereby form a mechanically stable gel-like material. The spongy gels are independent of a time-consuming or otherwise demanding in situ scaffold formation. As solvent evaporation from gels is a concern for various applications, we also studied solvent evaporation of wetting and non-wetting liquids dispersed in the sponge. [ABSTRACT FROM AUTHOR]

This study reports on gold nanoparticles (AuNPs) immobilized in a sponge made of short electrospun fibers (Au-sponge), which show surprisingly high reaction rates at extremely low gold amount. Au-sponges are made by freeze-drying of dispersions of short electrospun fibers with preimmobilization of AuNPs. The resulting Au-sponges show very low densities around 7 mg cm−3 corresponding to a pore volume of about 150 mL g−1, but low surface area and very low amount of AuNPs in the range of 0.29-3.56 wt%. In general, catalysts with immobilized AuNPs show much low reaction rates compared to systems with dispersed AuNPs. By contrast, the Au-sponge catalyst with immobilized AuNPs is discerned here as an extremely efficient catalyst even superior to other systems with dispersed AuNPs. The fidelity of the Au-sponges after reactions is good enough for manifold use and thereby provides a sustainable catalyst design as well. [ABSTRACT FROM AUTHOR]

Mechanically strong electrospun nanofibers at high temperature are highly desired in the aerospace industry, high temperature filtration and fire protection clothing. In the present work, highly tough poly(imide-co-benzoxazole) (PI-co-PBO) nanofiber belts with excellent thermal stability, mechanical properties and thermomechanical properties were produced from the highly viscous methoxy-containing polyamic acid (MeO-PAA) solution by electrospinning followed by thermal rearrangement. The chemical structures of the polymer nanofibers and the corresponding thermal rearrangement were confirmed by 1H-NMR, FT-IR and TGA. The mechanical properties and thermomechanical properties were characterized by a tensile test and thermomechanical analysis (TMA). The aligned nanofiber belts heat-treated at 450 °C (ANF-450) had the highest tensile strength of 559 MPa, a modulus of 11.2 GPa and a toughness of 12.0 J g−1, respectively, which were much higher than those of the pure PBO films made by thermal rearrangement. The TMA test showed that the ANF-450 exhibited a high tensile strength retention of 90% and a modulus retention of 94% at a high temperature of 200 °C. These excellent thermomechanical properties make electrospun PI-co-PBO nanofibers promising candidates in high temperature areas. [ABSTRACT FROM AUTHOR]

Ultralight polymer sponges are prepared by freeze-drying of dispersions of short electrospun fibers. In contrast to many other highly porous materials, these sponges show extremely low densities (<3 mg cm−3) in combination with low specific surface areas. The resulting hierarchical pore structure of the sponges gives basis for soft and reversibly compressible materials and to hydrophobic behavior in combination with excellent uptake for hydrophobic liquids. Owing to their large porosity, cell culturing is successful after hydrophilic modification of the sponges. [ABSTRACT FROM AUTHOR]

High mechanical performance materials at high temperature are highly desired for the materials used in high temperature industries. This study reports the aligned electrospun polyimide nanofiber belt (A-PI-NFB) fabricated from the electrospinning followed with imidization. The A-PI-NFB showed increased mechanical and thermal mechanical properties as increasing the imidization temperature. At room temperature, the A-PI-NFB imidized at 450 °C (A-PI-NFB-450) had the highest tensile strength (689 MPa) and E modulus (13.2 GPa). The thermomechanical analysis (TMA) and dynamic mechanical analysis (DMA) showed that A-PI-NFB-450 possessed 80% tensile strength and 90% modulus when heated at 300 and 350 °C in N 2 , respectively. These excellent properties made A-PI-NFB good candidates for use in high temperature filtration, protective clothes etc. [ABSTRACT FROM AUTHOR]

Abstract: Copolymers, poly(acrylonitrile-co-monobutylitaconate-co-n-butylacrylate) (copolyacrylonitrile, co-PANs) with different content of monobutyl itaconate (MBI) were synthesized by free radical polymerization and then electrospun into aligned nanofibers. After thermal treatments of stabilization, carbonization, and graphitization, the resulting aligned co-PAN nanofibers were converted to aligned electrospun carbon nanofiber bundles (ECNFB) with diameters of approximately 200nm. FT-IR technique was applied to investigate the stabilization process of co-PAN nanofibers, while XRD, TEM and tensile tester were used to characterize the microstructures and mechanical properties of the ECNFB. The measured results revealed that MBI was a fairly useful comonomer for preparing high performance PAN-based CNFs by improving the stabilization of co-PAN nanofibers and by promoting the formation of ordered graphite crystals in the ECNFB. When the content of MBI unit in co-PAN was 5wt%, the aligned ECNFB exhibited a tensile strength of up to 1.8GPa and a Young׳s modulus of up to 97.0GPa, which is 86% and 67% higher than those of the ECNFB previously reported in our group respectively. [Copyright &y& Elsevier]

Electrospinning is an effective and versatile method to prepare continuous polymer nanofibers and nonwovens that exhibit excellent properties such as high molecular orientation, high porosity and large specific surface area. Benefitting from these outstanding and intriguing features, electrospun nanofibers have been employed as a promising candidate for the fabrication of food packaging materials. Actually, the electrospun nanofibers used in food packaging must possess biocompatibility and low toxicity. In addition, in order to maintain the quality of food and extend its shelf life, food packaging materials also need to have certain functionality. Herein, in this timely review, functional materials produced from electrospinning toward food packaging are highlighted. At first, various strategies for the preparation of polymer electrospun fiber are introduced, then the characteristics of different packaging films and their successful applications in food packaging are summarized, including degradable materials, superhydrophobic materials, edible materials, antibacterial materials and high barrier materials. Finally, the future perspective and key challenges of polymer electrospun nanofibers for food packaging are also discussed. Hopefully, this review would provide a fundamental insight into the development of electrospun functional materials with high performance for food packaging. [ABSTRACT FROM AUTHOR]

Coaxial electrospinning is an attractive technology to produce core/sheath and hollow fibers. However, until now, the relatively low productivity has limited its broad applications. In this work, coaxial electrospinning with air‐blowing‐assistance is applied to improve the productivity of core/sheath and hollow fibers. Different core and shell materials are used for this electrospinning. The flow rate and air‐blowing rate during electrospinning are optimized. SEM and TEM are used to confirm the core/sheath and hollow structure of fibers. The results show that air‐blowing‐assisted electrospinning technology can be successfully applied for the large‐scale production of core/sheath and hollow fibers which open the path to new applications of this promising class of materials. [ABSTRACT FROM AUTHOR]

Compared with traditional metal materials, carbon-based materials have the advantages of low density, high conductivity, good chemical stability, etc., and can be used as reliable alternative materials in various fields. Among them, the carbon fiber conductive network constructed by electrospinning technology has the advantages of high porosity, high specific surface area and rich heterogeneous interface. In order to further improve the conductivity and mechanical properties of pure carbon fiber films, tantalum carbide (TaC) nanoparticles were selected as conductive fillers. The crystallization degree, electrical and mechanical properties of electrospun TaC/C nanofibers at different temperatures were investigated. As the carbonization temperature increases, the crystallization degree and electrical conductivity of the sample also increases, while the growth trend of electrical conductivity is markedly slowed. The best mechanical properties of 12.39 MPa was achieved when the carbonization temperature was 1200 °C. Finally, through comprehensive analysis and comparison, it can be concluded that a carbonization temperature of 1200 °C is the optimum. [ABSTRACT FROM AUTHOR]

Highlights: [•] Heat-resistant electrospun PBO nanofibers were prepared from precursor OH-PAA. [•] The obtained PBO nanofibers are thermally stable up to 643°C. [•] The obtained PBO nanofibers have excellent mechanical properties. [•] PBO nanofibers have retention of tensile strength and modulus over 80% at 350°C. [•] Such heat-resistant PBO nanofibers could be used in high temperature fields. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Electrospinning is a common method for preparing nanomaterials. Among many electrospinning materials, electrospun carbon nanofibers (CNFs) have become one of the hot research directions for advanced functional materials owing to their good mechanical properties, high surface area, excellent flexibility, physical and chemical stability. Particularly, significant progress has been made in the engineering advancement of electrospinning, electrospun CNFs and their derived reinforced composites to fulfill various applications. This review aims to afford a comprehensive overview of electrospun CNF reinforced composites. Firstly, the different precursors, the correlative properties, and surface modification strategies (e.g. , physical modification and chemical modification) of electrospun CNFs are introduced. Secondly, the preparation methods of reinforced composites based on electrospun CNFs are described in detail. Then, the functional applications of electrospun CNF reinforced composites are discussed. Finally, the challenges and future solutions of electrospun CNF reinforced composites are also prospected. This review is expected to offer a basic but deep understanding of modification strategies to heighten the surface performances of CNFs for the future development of high-performance electrospun CNF reinforced composites in the composite industry, defense, and aerospace applications. [Display omitted] • Electrospun CNF reinforced composites are widly used in engineering materials. • The precursors and modification strategies of electrospun CNFs are detailly reviewed. • Diverse preparation and application of CNF reinforced composites are summarized. • The current challenges of electrospun CNF reinforced composites are discussed. • The future prospects of CNF-based composites in advanced engineering are proposed. [ABSTRACT FROM AUTHOR]

Mechanical properties of polyimide (PI) electrospun nanofibers could be improved by increasing imidization temperatures. However, the intrinsic mechanism on this phenomenon is highly required, which is helpful to improve mechanical properties of electrospun nanofibers by external thermal treatment. In this work, single electrospun PI nanofibers (SNF-PI) with different imidization temperatures were prepared. The nanofiber morphology was studied by SEM and AFM and the mechanical properties were measured by single fiber micro-tensile test. Polarized Raman Spectroscopy was applied to determine the PI molecular orientation in SNF-PI. The molecular orientation factor provides directly explanation on the effect of imidization temperatures on the mechanical properties of SNF-PI. [ABSTRACT FROM AUTHOR]

[Display omitted] • The actuator can achieve synergistic movement of deformation and transportation. • Added Fe 3 O 4 NPs provide both magnetism and high-efficient photothermal conversion. • The hydrogel actuator owns high tensile-strength of 4.59 MPa via electrospinning. • The actuator can provide ultrafast deformational speed of 178°/s. • We have explored new bio-inspired systems with two/multi-step synergic actuation. As a soft/wet intelligent material, hydrogel actuators with multiple stimuli-responsiveness have been widely developed. However, it is still greatly difficult for them to integrate bi/multiple responsiveness together for bio-mimetic synergistic actuation. Here, we have explored a high-strength anisotropic bi-layer hydrogel actuator with P(NIPAM-ABP) layer and Fe 3 O 4 /PAN layer via electrospinning technique, which can provide programmable bi-functional synergistic movement. The Fe 3 O 4 /PAN layer can provide magnetic responsive navigation for long-range transportation on account of the magnetism of the Fe 3 O 4 nanoparticles. Furthermore, the ultrahigh photothermal conversion efficiency of the Fe 3 O 4 nanoparticles in the Fe 3 O 4 /PAN layer, can endow the P(NIPAM-ABP) layer with fast remotely-controlled photothermal-responsive deformation. Most importantly, this hydrogel actuator can achieve complex higher-level programmable movements than before based on the synergy of remotely-controlled deformation and the long-range transportation, which can be utilized to design various novel bio-mimetic soft-robots. Last but not least, the introduction of the electrospinning, not only can achieve high strength (4.59 MPa of tensile strength) of this bi-layer hydrogel, but also can provide both ultrafast (178°/s) and programmable complex photothermal-responsiveness, owing to the ultrahigh specific surface area (ultra-thin and porous structure) and excellent orientation of the thermal-responsive P(NIPAM-ABP) nanofibers respectively. This work will provide a general method via electrospinning for anisotropic hydrogel actuator with bi/multiple-functional synergy and will provide a new strategy for smart actuators and other bio-mimetic intelligent materials/systems. [ABSTRACT FROM AUTHOR]

An alternative magnetic field (AMF)-induced electrospun fibrous thermoresponsive composite actuator showing penetrable remote-control ability with fast response is shown here for the first time. The built-in heater of magnetothermal Fe3O4 nanoparticles in the actuator and the porous structure of the fibrous layer contribute to a fast actuation with a curvature of 0.4 mm−1 in 2 s. The higher loading amount of the Fe3O4 nanoparticles and higher magnetic field strength result in a faster actuation. Interestingly, the composite actuator showed a similar actuation even when it was covered by a piece of Polytetrafluoroethylene (PTFE) film, which shows a penetrable remote-control ability. [ABSTRACT FROM AUTHOR]

• Single PI/rGO composite nanofiber by in-situ polymerization and in-situ thermal conversion. • Tensile strength of single nanofiber up to 4.2 GPa (PI/rGO-1.0% single nanofiber). • Modulus of single nanofiber up to 121 GPa (PI/rGO-1.2% single nanofiber). • Homogeneous dispersion of rGO by in-situ strategies. • In-situ strategies enhance the interfacial interaction between rGO and PI fibrous matrix. High mechanical performance electrospun polymeric nanofibers are highly desired for practical applications, especially as reinforcements for composites. However, most of the electrospun polymeric nanofibers present tensile strength < 3 GPa. To overcome such limitation, this work successfully prepared single rGO reinforced polyimide composite nanofiber with tensile strength up to 4.2 GPa (PI/rGO-1.0%) and modulus up to 121 GPa (PI/rGO-1.2%) by applying in-situ polymerization, electrospinning, and in-situ thermal conversion. These mechanical properties are higher than other polymer-based electrospun nanofibers, and 45% and 236% higher than those of neat PI single nanofiber, respectively. The in-situ strategies provide the homogeneous dispersion of rGO in single electrospun nanofibers and enhance the interfacial interaction between rGO and PI. In addition, the PI/rGO composite nanofibers also present excellent thermal stability with glass transition temperature (T g) > 295 °C, and the 5% thermal decomposition temperature (T 5%) > 539 °C. This work would open a new route for the preparation of high performance electrospun nanofibers for composites. [ABSTRACT FROM AUTHOR]