High performance electrospun nanofibers could be used to fabricate nanofiber reinforced composites.

Interventions and policies for tackling air pollution issues exist and have been proven to be effective. Membrane materials of nanofibrous morphology are attractive for air filtration, and further alleviate the environmental issues. Electrospinning as a simple and versatile way to fabricate ultrafine fibers has been attracting tremendous attention. Herein, the recent researches and future trends of green electrospinning are expounded from the aspects of green degradable materials, green solution electrospinning, and solvent‐free electrospinning. The green degradable materials, including biomass materials, biosynthetic polymer materials, and chemical synthetic materials are reviewed. Following the concept of green electrospinning, electrospun polymer nanofibers via aqueous solution are discussed; additionally, further trends of solvent‐free electrospinning including melt‐electrospinning, anion‐curing electrospinning, UV‐curing electrospinning, thermo‐curing electrospinning, and supercritical CO2‐assisted electrospinning are highlighted. Furthermore, the applications of these electrospun nanofibrous membranes in the field of air filtration are discussed. In the end, the challenges of green electrospinning and future prospects are summarized. The development of green electrospinning is reviewed with an emphasis on current advanced solvent‐free research, where electrospun nanofibrous membranes are contributing to promising treatment strategies to solve environment issue.

polyaniline fi bers made during polymerization by fast mixing of aniline and oxidants provided porous fi brous fi lm. [ 22 ] Recently bending of a 20 mm long porous membrane based on cationic poly(ionic liquid), poly(3-cyanomethyl-1-vinylimidazolium bis(trifuoromethanesulfonyl)imide) and a carboxylic acid-substituted pillar arene into multiply wound coils in presence of vapors of organic solvents such as acetone was shown in 0.4 s, and the original shape was recovered in ≈3 s in air. [ 23 ] Electrospinning is an effective method to fabricate nanofi ber nonwoven mats with large surface area and porosity. [ 24 ] Several studies have been carried out in the recent time regarding use of temperature responsive polymers like PNIPAM in making nanofi ber nonwovens for applications such as drug release, cell culture, etc. [25][26][27][28][29] Electrospun nanofi bers with very fi ne diameter, high surface to volume ratio and porosity are highly promising for transferring the stimulus and mass transport in comparison to the corresponding bulk fi lms. [ 30,31 ] In this work, we report simple but versatile method of fabrication of superfast temperature-triggered actuators using electrospun porous fi brous double layer membranes based on crosslinked thermoresponsive PNIPAM. The state-of-the-art method of making actuators when applied to fi brous bilayer membranes provided new and unexpected results demonstrating a number of advantages: i) the actuation of mats is very fast (<1 s) even for thick and large sized samples; ii) the formation of 3D structures could be OPEN-CLOSED for many cycles without losing its form and size; iii) contrary to already reported PNIPAMbased bilayer fi lms, fi brous mats are unfolded at room temperature and folded at elevated temperature; iv) they demonstrate anisotropic actuation behavior. Change in fi ber diameters, swelling/ shrinking, and morphology at different temperatures correlates to the unusual actuation behavior. The developed approach would be highly useful in design of porous 3D bioscaffolds and electrodes, catalysis, drug release, energy storage, etc. in the future.For our approach we have used two photo-crosslinkable polymers. First polymer is hydrophobic, non-stimuli-responsive thermoplastic polyurethane (TPU) with small addition of photo-crosslinker (4-acryloylbenzophenone, ABP). Second polymer is thermoresponsive photo-crosslinkable copolymer of N -isopropylacrylamide with 2 mol.% of photo-crosslinker acryloylbenzophenone (P(NIPAM-ABP)). P(NIPAM-ABP) was prepared by free radical polymerization according to the literature procedure. [ 32 ] P(NIPAM-ABP) is stimuli-responsive polymer and demonstrates pronounced thermoresponsive properties and has LCST around T = 29 °C in pure water ( Figure S1, Supporting Information). The LCST of P(NIPAM-ABP) is slightly lower than LCST of pure PNIPAM ( T = 32 °C) that is due to presence of hydrophobic ABP moieties.Polymer mats made from individual polymers (TPU+ABP and P(NIPAM-ABP)) were prepared by electrospinning from concentrated polymer solution...

Increased energy consumption stimulates the development of various energy types. As a result, the storage of these different types of energy becomes a key issue. Supercapacitors, as one important energy storage device, have gained much attention and owned a wide range of applications by taking advantages of micro-size, lightweight, high power density and long cycle life. From this perspective, numerous studies, especially on electrode materials, have been reported and great progress in the advancement in both the fundamental and applied fields of supercapacitor has been achieved. Herein, a review of recent progress in carbon materials for supercapacitor electrodes is presented. First, the two mechanisms of supercapacitors are briefly introduced. Then, research on carbon-based material electrodes for supercapacitor in recent years is summarized, including different dimensional carbon-based materials and biomassderived carbon materials. The characteristics and fabrication methods of these materials and their performance as capacitor electrodes are discussed. On the basis of these materials, many supercapacitor devices have been developed. Therefore, in the third part, the supercapacitor devices based on these carbon materials are summarized. A brief overview of two types of conventional supercapacitor according to the charge storage mechanism is compiled, including their development process, the merits or withdraws, and the principle of expanding the potential range. Additionally, another fast-developed capacitor, hybrid ion capacitors as a good compromise between battery and supercapacitor are also discussed. Finally, the future aspects and challenges on the carbon-based materials as supercapacitor electrodes are proposed.

2850 wileyonlinelibrary.com large amounts of liquids and are excellent fi lters. Sponges with a volume of 1000 cm 3 can process up to 3000 L water h −1 . Furthermore, they can conduct light as discovered recently by Brümmer et al. [ 2 ] In addition, Natalio et al. reported on the formation of sponge skeletons shown to feature great bending strength and on the role of silicatein-α in the biomineralization of silicates in sponges, which accounts for the high reversible compressibility of sponges in spite of low densities. [ 3 ] Aizenberg et al. pointed out on the example of the so-called glass sponges ( Euplectella ) the important role of the hierarchical design from the nanometer to macroscopic length scale for structural materials. [ 4 ] The structural base of sponges are multiarmed spicules of silicate or calcium carbonate, which form highly porous structures of several hierarchical layers as shown in Figure 1 A,B. This leads to highly porous ultralight 3D materials (ultralight is defi ned when the density of material is <10 mg cm −3 ).[ 5 ] In recent literature, a variety of highly porous ultralight 3D materials were reported based on carbon, ceramics, and cellulose, which were characterized by porosities >99% and relatively high compressive strength. [6][7][8][9][10] Carbon and cellulose based sponges show ultralow densities and excellent mechanical properties but soft sponges with similar mechanical integrity are missing.Since spicules of natural sponges conspicuously resemble polymer fi bers, formation of such fi brous structures by electrospinning [ 11 ] could be a promising concept for the preparation of polymer-based biomimetic analogous of natural sponges and would open the huge potential of electrospun materials for 3D sponge-type structures. Indeed, 3D porous structures were prepared by electrospinning which was nicely summarized in comprehensive review in recent literature. [ 7 ] However, previous efforts of making 3D highly porous electrospun materials, for example, via ultrasonic treatment, resulted in higher densities and correspondingly lower porosities of <99%, [ 12 ] as well as relatively poor mechanical performance. Remarkably, Eichhorn et al. claimed that theoretically ultrahigh porosities of electrospun nonwovens >99% could not be achieved. [ 13 ] In contrast to these reports, we present here the formation of ultralight weight highly porous 3D electrospun polymer fi ber-based spongy structures with densities as low as 2.7 mg cm −3 corresponding to a porosity of 99.6%. They were prepared by electrospinning of a photo cross-linkable polymer followed by UV cross-linking, mechanical cutting, suspending cut fi bers in liquid dispersion, and freezedrying. These polymer sponges showed in analogy to natural Ultralight, Soft Polymer Sponges by Self-Assembly of Short Electrospun Fibers in Colloidal DispersionsGaigai Duan , Shaohua Jiang , Valérie Jérôme , Joachim H. Wendorff , Amir Fathi , Jaqueline Uhm , Volker Altstädt , Markus Herling , Josef Breu , Ruth Freitag , Seema Agarwal , and Andreas Gre...

Low-density macroporous sponges with densities less than 100 mg cm are both a challenge and an opportunity for advanced chemistry and material science. The challenge lies in the precise preparation of the sponges with property combinations that lead to novel applications. Bottom-up and top-down chemical and engineering methods for the preparation of sponges are a major focus of this Review, with an emphasis on carbon and polymer materials. The light weight, sustainability, breathability, special wetting characteristics, large mass transfer, mechanical stability, and large pore volume are typical characteristics of sponges made of advanced materials and could lead to novel applications. Some selected sponge properties and potential applications are discussed.

Tunable density, thermally and mechanically stable, elastic, and thermally insulating sponges are required for demanding applications. Hierarchically structured sponges with bimodal interconnected pores, porosity more than 99%, and tunable densities (between 7.6 and 10.1 mg/cm) are reported using polyimide (PI) as high temperature stable polymer. The sponges are made by freeze-drying a dispersion of short PI fibers and precursor polymer, poly(amic acid) (PAA). The concept of "self-gluing" the fibrous network skeleton of PI during sponge formation was applied to achieve mechanical stability without sacrificing the thermal properties. The sponges showed initial degradation above 400 and 500 °C in air and nitrogen, respectively. They have low thermal conductivity of 0.026 W/mK and thermal diffusivity of 1.009 mm/s for a density of 10.1 mg/cm. The sponges are compressible for at least 10 000 cycles and good thermal insulators even at high compressions. These fibrous PI sponges are promising candidates for potential applications in thermal insulation, lightweight construction, high-temperature filtration, sensors, and catalyst carrier for high-temperature reactions.

Thermoresponsive hydrogel fibrous membranes showing directionally controlled movements and surface change with ultra‐fast speed are presented for the first time. They show reversible coiling, rolling, bending, and twisting deformations in different controllable directions for many cycles (at least 50 cycles tried) with inside‐out change in surfaces and shapes. Speed, reversibility, large‐scale deformations and, most importantly, control over the direction of deformation is required in order to make synthetic actuators inspired from natural materials or otherwise. A polymeric synthetic material combining all these properties is still awaited. This issue is addressed and provide a very simple system fulfilling all these requirements by combining porosity and asymmetric swelling/shrinking via orientation of hydrogel fibers at different angles in a fibrous membrane. Electrospinning is used as a tool for making membranes with fibers oriented at different angles.