Three-dimensional nanofibrous aerogels (NFAs) that are both highly compressible and resilient would have broad technological implications for areas ranging from electrical devices and bioengineering to damping materials; however, creating such NFAs has proven extremely challenging. Here we report a novel strategy to create fibrous, isotropically bonded elastic reconstructed (FIBER) NFAs with a hierarchical cellular structure and superelasticity by combining electrospun nanofibres and the fibrous freeze-shaping technique. Our approach causes the intrinsically lamellar deposited electrospun nanofibres to assemble into elastic bulk aerogels with tunable densities and desirable shapes on a large scale. The resulting FIBER NFAs exhibit densities of 40.12 mg cm À 3 , rapid recovery from deformation, efficient energy absorption and multifunctionality in terms of the combination of thermal insulation, sound absorption, emulsion separation and elasticity-responsive electric conduction. The successful synthesis of such fascinating materials may provide new insights into the design and development of multifunctional NFAs for various applications.

Many applications proposed for functional nanofibers require their assembly into a monolithic cellular structure. The ability to maintain structural integrity upon large deformation is essential to ensure a macroscopic cellular material that functions reliably. However, it remains a great challenge to achieve high elasticity in three-dimensional (3D) nanofibrous networks. Here, we report a strategy to create fibrous, isotropically bonded elastic reconstructed (FIBER) aerogels with a hierarchical cellular structure and superelasticity by combining electrospun nanofibers and the freeze-shaping technique. Our approach allows the intrinsically lamellar deposited electrospun nanofibers to assemble into elastic bulk aerogels with tunable porous structure and wettability on a large scale. The resulting FIBER aerogels exhibit the integrated properties of ultralow density (<30 mg cm(-3)), rapid recovery from 80% compression strain, superhydrophobic-superoleophilic wettability, and high pore tortuosity. More interestingly, the FIBER aerogels can effectively separate surfactant-stabilized water-in-oil emulsions, solely using gravity, with high flux (maximum of 8140 ± 220 L m(-2) h(-1)) and high separation efficiency, which match well with the requirements for treating the real emulsions. The synthesis of FIBER aerogels also provides a versatile platform for exploring the applications of nanofibers in a self-supporting, structurally adaptive, and 3D macroscopic form.

Ultralight and fire-resistant ceramic nanofibrous aerogels with temperature-invariant superelasticity to 1100°C.

Freeze-casted nanofiber based sponges or aerogels exhibit a hierarchical porous structure. Pore formation is only partially understood. Therefore, we studied the underlying solid templating mechanism. We were able to tailor the secondary pore size between 9.5 and 123 µm while retaining the smaller primary pores known from electrospun nanofiber membranes. To understand the effect of microstructure on the sponges' bulk properties, mass flow through the pores and interaction with the sponges' internal surface were investigated. By solely altering the sponges' microstructure we indeed found tunability in permeability by a factor 7 and in filtration efficiency by a factor of 220. Hence, pore architecture of nanofiber based sponges is a key element for their performance. The selected pullulan/PVA polymer blends and aqueous electrospinning conditions are benign and allow the facile adaptation of these ultralight highly porous sponges for a large number of applications.

Compared with other methods of fiber preparation like drawing, template synthesis, self-assembly, phase separation, etc., electrospinning has emerged as a versatile and cost-effective method for producing long continuous fibers with diameters ranging from several micrometers down to a few nanometers by applying a high voltage on a polymer solution or melt 1 . In 1934, Formhals 2 described the operation of electrospinning in a US patent for the first time; but only since 1990s it has gained substantial attention. The process attracted rapidly growing interests in the past two decades triggered by potential Increasing demands for ever more sensitive sensors for global environmental monitoring, food inspection and medical diagnostics have led to an upsurge of interests in nanostructured materials such as nanofibers and nanowebs. Electrospinning exhibits the unique ability to produce diverse forms of fibrous assemblies. The remarkable specific surface area and high porosity bring electrospun nanomaterials highly attractive to ultrasensitive sensors and increasing importance in other nanotechnological applications. In this review, we summarize recent progress in developments of the electrospun nanomaterials with applications in some predominant sensing approaches such as acoustic wave, resistive, photoelectric, optical, amperometric, and so on, illustrate with examples how they work, and discuss their intrinsic fundamentals and optimization designs. We are expecting the review to pave the way for developing more sensitive and selective nanosensors. (BD) and mwang@lanl.gov (MW) Open access under CC BY-NC-ND license.

a b s t r a c tSince 2006, a rapid development has been achieved in a subject area, so called electro-spinning/netting (ESN), which comprises the conventional electrospinning process and a unique electro-netting process. Electronetting overcomes the bottleneck problem of electrospinning technique and provides a versatile method for generating spider-web-like nanonets with ultrafine fiber diameter less than 20 nm. Nano-nets, supported by the conventional electrospun nanofibers in the nano-fiber/nets (NFN) membranes, exhibit numerious attractive characteristics such as extremely small diameter, high porosity, and Steiner tree network geometry, which make NFN membranes optimal candidates for many significant applications. The progress made during the last few years in the field of ESN is highlighted in this review, with particular emphasis on results obtained in the author's research units. After a brief description of the development of the electrospinning and ESN techniques, several fundamental properties of NFN nanomaterials are addressed. Subsequently, the used polymers and the state-of-the-art strategies for the controllable fabrication of NFN membranes are highlighted in terms of the ESN process. Additionally, we highlight some potential applications associated with the remarkable features of NFN nanostructure. Our discussion is concluded with some personal perspectives on the future development in which this wonderful technique could be pursued.

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Developing a feasible and efficient separation membrane for the purification of highly emulsified oily wastewater is of significance but challenging due to the critical limitations of low flux and serious membrane fouling. Herein, a biomimetic and superwettable nanofibrous skin on an electrospun fibrous membrane via a facile strategy of synchronous electrospraying and electrospinning is created. The obtained nanofibrous skin possesses a lotus‐leaf‐like micro/nanostructured surface with intriguing superhydrophilicity and underwater superoleophobicity, which are due to the synergistic effect of the hierarchical roughness and hydrophilic polymeric matrix. The ultrathin, high porosity, sub‐micrometer porous skin layer results in the composite nanofibrous membranes exhibiting superior performances for separating both highly emulsified surfactant‐free and surfactant‐stabilized oil‐in‐water emulsions. An ultrahigh permeation flux of up to 5152 L m−2 h−1 with a separation efficiency of >99.93% is obtained solely under the driving of gravity (≈1 kPa), which was one order of magnitude higher than that of conventional filtration membranes with similar separation properties, showing significant applicability for energy‐saving filtration. Moreover, with the advantage of an excellent antioil fouling property, the membrane exhibits robust reusability for long‐term separation, which is promising for large‐scale oily wastewater remediation.