Scalable Fabrication of Electrospun True-Nanoscale Fiber Membranes for Effective Selective Separation

High-Performance Membranes Based on Spherical-Beaded Nanofibers and Nanoarchitectured Networks for Water-in-Oil Emulsion Separation

High-performance separation materials for oil-water emulsions are crucial to environmental protection and resource recovery; however, most existing fibrous separation materials are subject to large pore size and low porosity, resulting in limited separation performance. Herein, we create high-performance membranes consisting of spherical-beaded nanofibers and nanoarchitectured networks (nano-nets) using electrostatic spinning/netting technology, for water-in-oil emulsion separation. By manipulating the nonequilibrium stretching of jets, spherical-beaded nanofibers capable of generating a robust microelectric field are fabricated as scaffolds, on which charged droplets are induced to eject and phase separate to self-assemble nano-nets with small pores. Benefiting from 3D undulating networks with cavities originating from 2D nano-nets supported by 1D spherical-beaded nanofibers, the membranes exhibit under-oil superhydrophobicity (>152°), a striking separation performance with an efficiency of >99.2% and a flux of 5775 L m-2 h-1, together with wide pressure applicability, antifouling, and reusability. This work may open up new horizons in developing fibrous materials for separation and purification.

Fluorine-Free Amphiphobic SBS/PAN Micro/Nanofiber Membrane by Integrating Click Reaction with Electrospinning for Efficient and Recyclable Air Filtration

The membrane fouling derived from the accumulated dust pollutants and highly viscous oily particles causes irreversible damage to the filtration performance of air filters and results in a significant reduction in their service life. However, it is still challenging to construct high-efficiency and antifouling air filtration membranes with recyclable regeneration. Herein, the fluorine-free amphiphobic micro/nanofiber composite membrane was controllably constructed by integrating click chemistry reaction and electrospinning technique. Low-surface-energy fibers were constructed by a thiol-ene click chemical reaction between mercaptosilane and vinyl groups of polystyrene-butadiene-styrene (SBS), combined with hydroxyl-terminated poly(dimethylsiloxane) during the electrospinning process. The functional air filter is then prepared by the two-layer composite strategy. Because of the advantages of liquid-like fibrous surface and micro/nanofibrous porous structure, SBS/PAN composite membrane simultaneously shows superior antifouling performances of pollutants and filtration efficiency of over 97% PM0.3 removal. More importantly, the antifouling fibrous membrane still presents a stable and efficient filtration efficiency after multiple washes. Its service life in dust filtration environments is approximately 1.7 times longer than that of the substrate membrane. This work may provide a significant reference for the design of antifouling fiber membranes and high-efficiency air filters with long life spans and reusability.

Bio-inspired gradient poly(lactic acid) nanofibers for active capturing of PM0.3 and real-time respiratory monitoring

The concept of bio-inspired gradient hierarchies, in which the well-defined MOF nanocrystals serve as active nanodielectrics to create electroactive shell at poly(lactic acid) (PLA) nanofibers, is introduced to promote the surface activity and electroactivity of PLA nanofibrous membranes (NFMs). The strategy enabled significant refinement of PLA nanofibers during coaxial electrospinning (∼40 % decline of fiber diameter), accompanied by remarkable increase of specific surface area (nearly 1.5 m2/g), porosity (approximately 85 %) and dielectric constants for the bio-inspired gradient PLA (BG-PLA) NFMs. It largely boosted initial electret properties and electrostatic adsorption capability of BG-PLA NFMs, as well as charge regeneration by TENG mechanisms even under high-humidity environment. The BG-PLA NFMs thus featured exceptionally high PM0.3 filtration efficiencies with well-controlled air resistance (94.3 %, 163.4 Pa, 85 L/min), in contrast to the relatively low efficiency of only 80.0 % for normal PLA. During the application evaluation of outdoor air purification, excellent long-term filtering performance was demonstrated for the BG-PLA for up to 4 h (nearly 98.0 %, 53 Pa), whereas normal PLA exhibited a gradually declined filtration efficiency and an increased pressure drop. Moreover, the BG-PLA NFMs of increased electroactivity were ready to generate tribo-output currents as driven by respiratory vibrations, which enabled real-time monitoring of electrophysiological signals. This bio-inspired gradient strategy opens up promising pathways to engender biodegradable nanofibers of high surface activity and electroactivity, which has significant implications for intelligent protective membranes.

Flexible Strain Sensors Based on Thermoplastic Polyurethane Fabricated by Electrospinning: A Review

Over recent years, thermoplastic polyurethane (TPU) has been widely used as a substrate material for flexible strain sensors due to its remarkable mechanical flexibility and the ease of combining various conductive materials by electrospinning. Many research advances have been made in the preparation of flexible strain sensors with better ductility, higher sensitivity, and wider sensing range by using TPU in combination with various conductive materials through electrospinning. However, there is a lack of reviews that provide a systematic and comprehensive summary and outlook of recent research advances in this area. In this review paper, the working principles of strain sensors and electrospinning technology are initially described. Subsequently, recent advances in strain sensors based on electrospun TPU are tracked and discussed, with a focus on the incorporation of various conductive fillers such as carbonaceous materials, MXene, metallic materials, and conductive polymers. Moreover, the wide range of applications of electrospun TPU flexible strain sensors is thoroughly discussed. Finally, the future prospects and challenges of electrospun TPU flexible strain sensors in various fields are pointed out.

Ultrathin, ultralight dual-scale fibrous networks with high-infrared transmittance for high-performance, comfortable and sustainable PM0.3 filter

Highly permeable particulate matter (PM) can carry various bacteria, viruses and toxics and pose a serious threat to public health. Nevertheless, current respirators typically sacrifice their thickness and base weight for high-performance filtration, which inevitably causes wearing discomfort and significant consumption of raw materials. Here, we show a facile yet massive splitting eletrospinning strategy to prepare an ultrathin, ultralight and radiative cooling dual-scale fiber membrane with about 80% infrared transmittance for high-protective, comfortable and sustainable air filter. By tailoring antibacterial surfactant-triggered splitting of charged jets, the dual-scale fibrous filter consisting of continuous nanofibers (44 ± 12 nm) and submicron-fibers (159 ± 32 nm) is formed. It presents ultralow thickness (1.49 μm) and base weight (0.57 g m-2) but superior protective performances (about 99.95% PM0.3 removal, durable antibacterial ability) and wearing comfort of low air resistance, high heat dissipation and moisture permeability. Moreover, the ultralight filter can save over 97% polymers than commercial N95 respirator, enabling itself to be sustainable and economical. This work paves the way for designing advanced and sustainable protective materials.

Highly Efficient Fabrication of Biomimetic Nanoscaled Tendrils for High-Performance PM0.3 Air Filters

Particulate matter pollution has become a serious public health issue, especially with the outbreak of new infectious diseases. However, most existing air filtration materials face challenges such as being too bulky, having high resistance, and a trade-off between filtration efficiency and air permeability. Here, a unique electro-blown spinning technique is used to prepare an air filter made of biomimetic nanoscaled tendril nonwovens (Nano-TN). The introduction of an airflow field significantly increases the whipping frequency and the strain mismatch of composite jets, achieving large-scale and highly efficient preparation of Nano-TN. The resultant Nano-TN has an ultrahigh porosity (97%) and a small pore size (2.9 μm). At the same filtration level, its air resistance is 37% lower than that of traditional straight nanofibrous nonwovens and has a higher dust-holding capacity. Moreover, compared with traditional three-dimensional air filters, the Nano-TN filter is thinner, offering tremendous application prospects in various environmental purification and personal protection fields.

Diphylleia Grayi-Inspired Intelligent Temperature-Responsive Transparent Nanofiber Membranes

Nanofiber membranes (NFMs) have become attractive candidates for next-generation flexible transparent materials due to their exceptional flexibility and breathability. However, improving the transmittance of NFMs is a great challenge due to the enormous reflection and incredibly poor transmission generated by the nanofiber-air interface. In this research, we report a general strategy for the preparation of flexible temperature-responsive transparent (TRT) membranes, which achieves a rapid transformation of NFMs from opaque to highly transparent under a narrow temperature window. In this process, the phase change material eicosane is coated on the surface of the polyurethane nanofibers by electrospray technology. When the temperature rises to 37 °C, eicosane rapidly completes the phase transition and establishes the light transmission path between the nanofibers, preventing light loss from reflection at the nanofiber-air interface. The resulting TRT membrane exhibits high transmittance (> 90%), and fast response (5 s). This study achieves the first TRT transition of NFMs, offering a general strategy for building highly transparent nanofiber materials, shaping the future of next-generation intelligent temperature monitoring, anti-counterfeiting measures, and other high-performance devices.

High-Performance Liquid-Repellent and Thermal-Wet Comfortable Membranes Using Triboelectric Nanostructured Nanofiber/Meshes

Skin-like functional membranes with liquid resistance and moisture permeability are in growing demand in various applications. However, the membranes have been facing a long-term dilemma in balancing waterproofness and breathability, as well as resisting internal liquid sweat transport, resulting in poor thermal-wet comfort. Herein, a novel electromeshing technique, based on manipulating the ejection and phase separation of charged liquids, is developed to create triboelectric nanostructured nano-mesh consisting of hydrophobic ferroelectric nanofiber/meshes and hydrophilic nanofiber/meshes. By combining the true nanoscale diameter (≈22 nm), small pore size, and high porosity, high waterproofness (129 kPa) and breathability (3736 g m-2 per day) for the membranes are achieved. Moreover, the membranes can break large water clusters into small water molecules to promote sweat absorption and release by coupling hydrophilic wicking and triboelectric field polarization, exhibiting a satisfactory water evaporation rate (0.64 g h-1 ) and thermal-wet comfort (0.7 °C cooler than the cutting-edge poly(tetrafluoroethylene) protective membranes). This work may shed new light on the design and development of advanced protective textiles.

High-Performance Waterproof, Breathable, and Radiative Cooling Membranes Based on Nanoarchitectured Fiber/Meshworks

Smart membranes with protection and thermal-wet comfort are highly demanded in various fields. Nevertheless, the existing membranes suffer from a tradeoff dilemma of liquid resistance and moisture permeability, as well as poor thermoregulating ability. Herein, a novel strategy, based on the synchronous occurrence of humidity-induced electrospinning and electromeshing, is developed to synthesize a dual-network structured nanofiber/mesh for personal comfort management. Manipulating the ejection, deformation, and phase separation of spinning jets and charged droplets enables the creation of nanofibrous membranes composed of radiative cooling nanofibers and 2D nanostructured meshworks. With a combination of a true-nanoscale fiber (∼70 nm) in 2D meshworks, a small pore size (0.84 μm), and a superhydrophobic surface (151.9°), the smart membranes present high liquid repellency (95.6 kPa), improved breathability (4.05 kg m-2 d-1), and remarkable cooling performance (7.9 °C cooler than commercial cotton fabrics). This strategy opens up a pathway to the design of advanced smart textiles for personal protection.

Two-Dimensional Nanofibrous Networks by Superspreading-Based Phase Inversion for High-Efficiency Separation

Two-dimensional (2D) nanomaterials have been widely applied as building blocks of nanoporous materials for high-precision separations. However, most existing 2D nanomaterials suffer from poor continuity and a lack of interior linking, resulting in deteriorated performance when assembled into macroscopic bulk structures. Here, a unique superspreading-based phase inversion technique is proposed to directly construct 2D nanofibrous networks (NFNs) from a polymer solution. By tailoring capillary behavior, polymer solution droplets evolve into ultrathin liquid films through superspreading; manipulating phase instability, subsequently, enables the liquid film to phase invert into continuous nanostructured networks. The assembled single-layered NFNs possess integrated structural superiorities of 1D nanoscale fiber diameter (∼40 nm) and 2D lateral infinity, exhibiting a weblike nanoarchitecture with extremely small through-pores (∼100 nm). Our NFNs show remarkable performances in air filtration (PM0.3 removal) and water purification (microfiltration level). This creation of such attractive 2D fibrous nanomaterials can pave the way for versatile high-performance separation applications.

Preparation of fluffy bimodal conjugated electrospun poly(lactic acid) air filters with low pressure drop

Electrospun nanofiber membranes have been extensively studied as air filters. However, their limited filtration efficiency for submicron inhalable particulate matter (PM), high resistance to filtration, and limited capacity to hold dust have hindered their widespread use. The majority of materials come from petroleum, and the use of organic solvents during the spinning process has a significant negative impact on the environment. In this work, a sustainable method has been proposed for producing filters using poly(lactic acid) (PLA) with a bimodal diameter distribution through conjugated electrospinning. This technique allows for the continuous production of interconnected micro/nano hybrid porous membranes, resulting in reduced resistance and improved dust holding capacity. The filtration efficiency, pressure drop, long-term filtration performance, and actual performance of the conjugated bimodal membrane (CBM) were extensively investigated. The results indicate that the filter has a high capacity for retaining particles, with filtration efficiencies of 99.94% for PM 0.3 and 99.96% for PM 2.5. It also demonstrates a high quality factor (0.078 Pa-1 for PM 0.3 and 0.084 Pa-1 for PM 2.5), long-term stability (a decrease of 2.35% for PM 0.3 and 0.05% for PM 2.5 over a period of 60 days) and outstanding dust holding capacity (9.17 g m-2). The conjugated bimodal membrane (CBM) shows a 22.64% decrease in resistance compared to the non-conjugated bimodal membrane (BM). In general, the approach outlined in this work provides valuable insights into the development of high-performance biodegradable air filters. These filters have improved filtration efficiency and reduced resistance.

Facile In Situ Assembly of Nanofibers within Three-Dimensional Porous Matrices with Arbitrary Characteristics for Creating Biomimetic Architectures

It is challenging to recapitulate the natural extracellular matrix's hierarchical nano/microfibrous three-dimensional (3D) structure with multilevel pores, good mechanical and hydrophilic properties, and excellent bioactivity for designing and developing advanced biomimetic materials. This work reports a new facile strategy for the scalable manufacturing of such a 3D architecture. Natural polymers in an aqueous solution are interpenetrated into a 3D microfibrous matrix with arbitrary shapes and property characteristics to self-assemble in situ into a nanofibrous network. The collagen fiber-like hierarchical structure and interconnected multilevel pores are achieved by self-assembly of the formed nanofibers within the 3D matrix, triggered by a simple cross-linking treatment. The as-prepared alginate/polypropylene biomimetic matrices are bioactive and have a tunable mechanical property (compressive modulus from ∼17 to ∼24 kPa) and a tunable hydrophilicity (water contact angle from ∼94° to 63°). This facile and versatile strategy allows eco-friendly and scalable manufacturing of diverse biomimetic matrices or modification of any existing porous matrices using different polymers.

Electroactive, Antibacterial, and Biodegradable Poly(lactic acid) Nanofibrous Air Filters for Healthcare

Poly(lactic acid) (PLA)-based nanofibrous membranes (NFMs) hold great potential in the field of biodegradable filters for air purification but are largely limited by the relatively low electret properties and high susceptibility to bacteria. Herein, we disclosed a facile approach to the fabrication of electroactive and antibacterial PLA NFMs impregnated with a highly dielectric photocatalyst. In particular, the microwave-assisted doping (MAD) protocol was employed to yield Zn-doped titanium dioxide (Zn-TIO), featuring the well-defined anatase phase, a uniform size of ∼65 nm, and decreased band gap (3.0 eV). The incorporation of Zn-TIO (2, 6, and 10 wt %) into PLA gave rise to a significant refinement of the electrospun nanofibers, decreasing from the highest diameter of 581 nm for pure PLA to the lowest value of 264 nm. More importantly, dramatical improvements in the dielectric constants, surface potential, and electret properties were simultaneously achieved for the composite NFMs, as exemplified by a nearly 94% increase in surface potential for 3-day-aged PLA/Zn-TIO (90/10) compared with that of pure PLA. The well regulation of morphological features and promotion of electroactivity contributed to a distinct increase in the air filtration performance, as demonstrated by 98.7% filtration of PM_0.3 with the highest quality factor of 0.032 Pa^-1 at the airflow velocity of 32 L/min for PLA/Zn-TIO (94/6), largely surpassing pure PLA (89.4%, 0.011 Pa^-1). Benefiting from the effective generation of reactive radicals and gradual release of Zn²⁺ by Zn-TIO, the electroactive PLA NFMs were ready to profoundly inactivate Escherichia coli and Staphylococcus epidermidis. The exceptional combination of remarkable electret properties and excellent antibacterial performance makes the PLA membrane filters promising for healthcare.

Moisture wicking textiles with hydrophilic oriented polyacrylonitrile layer: Enabling ultrafast directional water transport

Functional textiles with high-performance directional water transport for regulating human sweat are in high demand because of growing concerns about the role of comfort in the performance of wearer. However, the fabrication of such materials remains a critical job. Here, we report a facile strategy to develop hydrophilic oriented polyacrylonitrile (HOPAN)/hydrophilic polylactic acid @polyvinylidene fluoride (HPLA@PVDF) composite membrane with surface energy gradient for enhanced directional water transport. Three step fabrication strategy involves electrospinning of oriented polyacrylonitrile (OPAN fibers) on polylactic acid (PLA) nonwoven surface followed by dip-coating in hydrophilic agent, and single-side electrospray of PVDF dilute solution on HOPAN/HPLA. Combination of highly oriented fiber structure, differential pore size and asymmetric wettability between two layers enabled instant water transport. The resultant fabricated composite membranes offer superior properties with one-way transport capacity (R) of 1117%, overall moisture management capacity (OMMC) of 0.91, and excellent water vapor transmission rate of 11.6 kg m^-2 d^-1. The successful preparation of these fascinating directional water transport materials offers new insight into the role of fiber alignment along with differential apertures and asymmetric chemical structure for realizing membranes for quick-drying applications.