Electrospun Polyimide Nanofibers Research Articles

Molecularly and Structurally Designed Polyimide Nanofiber Radiative Cooling Films for Spacecraft Thermal Management

AbstractRadiative cooling films (RCFs) are crucial for spacecraft thermal management, but their optical performance is currently limited by their structures and intrinsic high absorption at short wavelengths. In this study, a novel RCF using electrospun polyimide nanofibers optimized at both the molecular and microscale levels is developed. The newly designed polyimide molecules significantly decrease visible and ultraviolet (UV) light absorption while maintaining excellent thermal radiation properties in the infrared spectrum. By optimizing the diameter and orientation of the nanofibers using Monte Carlo simulations, the resulting film achieves a solar reflectivity of 99.6% and a mid‐infrared emissivity of 0.93. Its physical structures and optical properties remain stable under exposure to UV light, atomic oxygen, and extreme temperature changes. Further vacuum radiative cooling tests reveal that the thermal equilibrium temperature of this film is approximately 28 °C lower than that of Kapton‐based RCFs currently used in spacecraft. These results provide a new approach for creating efficient thermal management materials for space applications, with potential for broader use in architecture, electronic devices, and outdoor equipment.

Achieving an Ultralow-κ yet Strong and Transparent Film by Antisolvent-Confined Nanowelding of Electrospun Polyimide Nanofibers.

Developing ultralow-κ (dielectric constant) polyimides (PIs) that are mechanically robust while also being optically transparent is challenging. For the first time, we report a nanoporous PI film with an ultralow κ of 1.8 in combination with a tensile strength of up to 180 MPa, a Young's modulus of up to 6 GPa, and a transmittance of ∼88%. This is achieved by direct nanowelding of a porous electrospun PI nanofiber membrane using a simple mixture of ethanol-dominating DMAc. Benefiting from the effective evaporation of the antisolvent ethanol upon heating, the proposed nanowelding approach allows for the localized surface dissolution of the PI nanofibers, which enables the dissolved PI to "glue" the nanofibers and occupy vacant space in the membrane, resulting in the formation of a dense but nanoporous self-reinforced nanocomposite film. Our findings provide a renewed understanding of the potential of electrospun nanofibrous materials, and the underlying principle can hopefully be applied to other commodity polymers.

Cross-Linking Synergistic Effects to Enhance the Comprehensive Properties of Electrospun Polyimide Nanofiber Membranes for Advanced Lithium-Ion Batteries

Cross-Linking Synergistic Effects to Enhance the Comprehensive Properties of Electrospun Polyimide Nanofiber Membranes for Advanced Lithium-Ion Batteries

Laser‐Induced Carbon Nanofiber‐Based Redox Cycling System

AbstractRedox cycling is a powerful amplification strategy for reversible redox species within miniaturized electrochemical sensors. Herein, we generate three‐dimensional (3D) porous carbon nanofiber electrodes by CO2 laser‐writing on electrospun polyimide (PI) nanofiber mats, referred to as laser‐induced carbon nanofibers (LCNFs). The technique allowed the fabrication of interdigitated electrode (IDE) arrays with finger width and gap distance of ~400 μm and ~40 μm, respectively, offering approximately 3.5 times amplification efficiency (AF) and 95 % collection efficiency (CE). Such dimensions could not be achieved with IDEs fabricated on conventional PI film because the devices were short‐circuited. Stacked electrodes were also constructed as an alternative to the IDE design. Here, nanofiber mats as thin as ~20 μm were fabricated and used as vertical insulation between two LCNF band electrodes. While redox cycling efficiency was similar, the IDE design is more favorable considering the lower complexity and better signal reproducibility. Our strategy thus paves the way for creating flexible 3D porous electrodes with redox cycling ability that can be integrated into microfluidics and lab‐on‐a‐chip systems. In particular, the devices offer inherent flow‐through features in miniaturized analytical devices where separation and sensitive detection could be further realized.

Bifunctional polyimide/ZIF8 composite nanofibrous membranes with controllable bilayer structure for bioprotective application and high-efficiency oil/water separation

A multi-use fibrous filter medium composed of an electrospun polyimide (PI) nanofiber layer and a functional zeolitic imidazolate framework-8 (ZIF8) nanofilm layer was successfully fabricated to cope with the complex environmental pollution issues. The nanofilm layer consists of the anti-microbial ZIF8 converted from non-toxic zinc oxide (ZnO) nanocoating on PI fibers. One-step magnetron sputtering is utilized to deposit the ZnO nanocoating for the sake of desired functionality conformally onto the PI nanofibrous membrane without sacrificing its bulk structure and mechanical performance. The as-prepared PI/ZIF8 nanofibrous filter medium showed conspicuous biocidal efficacy and excellent interception ratio against gram-negative Escherichia coli (>99.9%) and gram-positive Staphylococcus aureus (>99.9%) within 20 min contact. Besides, compared with commercial media, the bilayer PI/ZIF8 fibrous medium showed exceptional thermal-wet comfortability due to the high porosity that could realize effective heat and humidity conduction. Moreover, the PI/ZIF830 NFM still present a high filtration efficiency of 99.6% towards PM0.3 even after treated at 300 °C for 1 h. Furthermore, the PI/ZIF830 NFM with a fiber basis weight of 1.8 g/m2 was endowed with a permeate flux of 17,279.2 L/m2/h and a high oil/water separation efficiency of > 99.6% because of the hydrophobicity and superoleophilicity. We envision that the antimicrobial, thermal-wet comfort, multi-use fibrous membrane will serve as a core-medium of environmentally-friendly platform for bioprotective equipment against future pathogen threats or oily wastewater treatment.

Flexible three-axis tactile sensor based on double-layer electrospun polyimide nanofiber membrane

Flexible three-axis tactile sensor based on double-layer electrospun polyimide nanofiber membrane

Freestanding 3D-interconnected carbon nanofibers as high-performance transducers in miniaturized electrochemical sensors

3D-carbon nanomaterials have proven to be high-performance transducers in electrochemical sensors but their integration into miniaturized devices is challenging. Herein, we develop printable freestanding laser-induced carbon nanofibers (f-LCNFs) with outstanding analytical performance that furthermore can easily allow such miniaturization through a paper-based microfluidic strategy. The f-LCNF electrodes were generated from electrospun polyimide nanofibers and one-step laser carbonization. A three-electrode system made of f-LCNFs exhibited a limit of detection (LOD) as low as 1 nM (S/N = 8) for anodic stripping analysis of silver ions, exhibiting the peak at ca. 100 mV vs f-LCNFs RE, without the need of stirring. The as-described system was implemented in miniaturized devices via wax-based printing, in which their electroanalytical performance was characterized for both outer- and inner-sphere redox markers and then applied to the detection of dopamine (the peak appeared at ca. 200 mV vs f-LCNFs RE) with a remarkable LOD of 55 pM. When modified with Nafion, the f-LCNFs were highly selective to dopamine even against high concentrations of uric and ascorbic acids. Especially the integration into closed microfluidic systems highlights the strength 3D porous structures provides excellent analytical performance paving the way for their translation to affordable lab-on-a-chip devices where mass-production capability, unsophisticated fabrication techniques, transfer-free, and customized electrode designs can be realized.Graphical abstract

Malachite Green Optical Sensor Based on Electrospun Polyimide Nanofiber

Malachite green (MG) is a triphenylmethane cationic dye used in aquaculture practice, although it has been banned in several countries. The illegal use by fish producers, however, persists due to its effectiveness, and ready and cheap supply. To prevent indiscriminate applications, strict control measures with simple analytical approaches are therefore necessary. With this purpose, a novel, cheap and simple method applying electrospun polyimide nanofibers was developed and validated for MG control in water by color image analysis. For detection, a simple apparatus and ImageJ® software to treat images captured by common smartphones were used. A detection limit of 0.013 mg/L with a linear analytical response range within the concentration of 0.05 to 0.3 mg/ L of malachite green (MG) with a correlation coefficient of 0.997 and standard deviation (n = 9) varying from 1.01 to 3.92% was achieved with the proposed method. Accuracy was assessed by recovery assays in water samples and percentages of 96.6 to 102.0% were obtained. The method is robust and suitable for the rapid and reliable monitoring of MG in water.

PI-LATP-PEO Electrolyte with High Safety Performance in Solid-State Lithium Metal Batteries

Although lithium metal is extensively used as an anode material for next-generation secondary batteries, the lithium metal reacts with the commonly used organic electrolytes, forming lithium dendrites, resulting in short-circuiting of batteries, which is a safety hazard. Solid-state electrolytes are a feasible solution to overcome these limitations. We prepared a PI–PEO–LATP composite solid electrolyte by compounding poly(ethylene oxide) (PEO) and Li1.4Al0.4Ti1.6(PO4)3 (LATP) with an electrospun polyimide (PI) nanofiber membrane using a solution-casting method. The best electrochemical and battery performance was obtained when the ratio of LATP to PEO was 15%. LATP reduces the crystallinity of PEO and increases its ionic conductivity. The 3,3′,4,4′-biphenyltetracarboxylic dianhydride-4,4′-oxydianiline PI nanofibrous membrane exhibited enhanced thermal stability and self-extinguishing performance. The lithium symmetric battery assembled with the PI–PEO–LATP composite solid electrolyte functioned stably for 1000 h at a current density of 0.5 mA·cm–2. The solid electrolyte showed good compatibility with a lithium metal anode and could inhibit the growth of lithium dendrites. When using the LiNi0.8Co0.1Mn0.1O2 positive electrode and lithium metal negative electrode, the assembled coin cell maintained a discharge capacity of 170.7 mAh·g–1 after 100 cycles at 0.2 C, with a capacity retention rate of 95% and Coulombic efficiency of approximately 100%.

Thermal conductivity of graphite nanofibers electrospun from graphene oxide-doped polyimide

Aromatic polyimide (PI)-based graphite nanofibers were obtained from the graphitization of graphene oxide (GO)-doped electrospun PI nanofibers. GO improves the PI molecular orientation, crystalline structure and thermal conductivity of the resulting nanofibers. The degree of PI molecular orientation in the nanofibers is increased by the GO during fiber preparation. This improvement in molecular orientation produces an increase in the thermal conductivity of the graphite nanofibers, and the addition of only 0.1% GO has a significant effect. The GO not only affects the thermal conductivity, but improves the PI molecular orientation and its role as nucleation centers during graphitization. This approach and the resulting high thermal conductivity materials show great potential for practical applications.

Electrospun polyimide-based thin-film composite membranes for organic solvent nanofiltration

Electrospun polymeric membranes are promising substrates for thin-film composite (TFC) membranes due to their unique interconnected pores and high porosity. However, it is still challenging to fabricate desirable electrospun substrates for organic solvent nanofiltration (OSN) owing to the relatively complex processing procedures and the organic operating environment. In this work, solvent-resistant electrospun polyimide (PI) nanofiber substrates were successfully fabricated through electrospinning followed by chemical cross-linking and heat-pressing. The cross-linking step improved the solvent tolerance of the membranes, while the heat-pressing step reduced the substrate pore size and surface roughness. However, it was found that heat-pressing at high temperatures (>140 °C) could degrade the cross-linking of PI, undermining their solvent-resistant property. A polyamide thin film layer was then synthesized on the solvent-resistant electrospun nanofibrous substrates via interfacial polymerization using reactant monomers m-phenylenediamine (MPD) and trimesoyl chloride (TMC). The TFC membranes exhibited excellent acetonitrile and acetone permeabilities of 31.28 ± 1.93 and 26.58 ± 1.13 L m−2 h−1 bar−1, respectively, with acid fuchsin (585 Da) and methyl orange (327 Da) rejections of 98.55 ± 1.24% and 92.42 ± 1.66%, respectively, in acetone. This study successfully demonstrated the potential use of electrospun PI nanofibers substrates for TFC membranes in OSN.

Reduced shrinkage and mechanically strong dual-network polyimide aerogel films for effective filtration of particle matter

Polyimide (PI) aerogel materials have been proven to have wide application potential in the fields of electronics, heat insulation, filtration, sensors, etc. due to high specific surface area and unique nanoporous structure. However, dimensional instability and poor tensile properties has been regarded as issues that limits its application, especially aerogel membranes, under severe temperatures. In this work, the electrospun polyimide nanofiber (PINF) membrane has been used as a self-reinforced template to successfully prepare PI composite aerogel membranes with greatly improved mechanical properties. The tensile strength can reach about 9–11 MPa, which is significantly higher than the corresponding pure PI aerogel film. At the same time, the composite aerogels also show good dimensional stability even after high temperature treatment. More importantly, observed by scanning electron microscope (SEM), PI composite aerogel films with hierarchical porous structure can be effectively constructed by adjusting the solid content of PI sol, especially at a low solid content of 1 wt%. In addition, the unique nanoporous structure between nanofibers makes it possible to maintain high filtration efficiency (99.91% for PM2.5) at a small basis weight.

Facile strategy to prepare polyimide nanofiber assembled aerogel for effective airborne particles filtration

Polyimide nanofiber (PINF) aerogel materials have received extensive attention as heat insulation, sensors and filtration media due to their excellent thermodynamic properties and unique porous structure. However, PINF must be difficult to disperse in organic solvents (dioxane or dimethyl sulfoxide) and dimensional instability has been regarded as issues that limits the preparation of PINF aerogels, especially in the water. So, it is of great significance to prepare polyimide aerogels with stable structure using water as a dispersant. In this work, the electrospun polyimide nanofiber precursor (polyamic acid (PAA) nanofiber (PAANF)) is uniformly dispersed in water, and triethylamine is added to terminated PAA oligomer as a binder. The resultant PINF aerogel has excellent mechanical properties with outstanding elasticity and a maximum compressive stress of 7.03 kpa at 50% strain. Furthermore, due to the extremely high porosity (98.4%) and hierarchical porous structure, the aerogel exhibits a high filtration efficiency (99.83%) for PM2.5, while the pressure drop is lower than that of the corresponding nanofiber membrane materials, which will facilitate its application in high temperature filtration and other fields.

Electrospun Poly[poly(2,5-benzophenone)]bibenzopyrrolone/polyimide nanofiber membrane for high-temperature and strong-alkali supercapacitor

The separator is an important component for energy storage devices. At present, the membranes for supercapacitors are rare, especially the ones that work with an alkaline electrolyte. Herein, a type of flexible and highly porous polymer hybrid nanofiber membrane was prepared via a facile electrospinning process and served as a separator for supercapacitor’s work with strong alkaline electrolyte. As obtained, poly[poly(2,5-benzophenone)]bibenzopyrrolone/polyimide (PBPY/PI) membrane showed good thermal stability, high mechanical strength, large electrolyte uptake (452%), and fast ion conductivity (0.68 mS/cm). Moreover, PBPY/PI membrane exhibited excellent alkali resistance. The supercapacitor assembled with PBPY/PI membrane showed much better performance than those assembled with a commercial polypropylene membrane and electrospun polyimide nanofiber membrane and was found without capacitance loss after charge/discharge at 30 A/g for 10,000 cycles at 80 °C. The PBPY/PI membrane is a good candidate with temperature resistance and alkali resistance for high-performance supercapacitors.

(Invited) Design of Electrospun Polyimide-Based Separators for Electrical Double-Layer Capacitors and Lithium-Ion Batteries

Separators are one of the very important components in the energy storage devices such as electrical double-layer capacitors (EDLCs) and Li-ion batteries (LIBs). The basic requirements for a suitable separator include high ionic transportation capability, good chemical stability, strong mechanical strength, and good thermo-dimensional stability. In order to reach the above requirements, in this work, we prepare the polyimide (PI) nanofibers with a controllable thickness via the electrospinning method. The introduction of Al2O3 nanoparticles significantly enhances the mechanical strength and ion conductivity of electrospun PI nanofibers. The as-prepared PI and PI@Al2O3 separators are tested for the EDLC and LIB applications. The functions of separators can be added onto the PI separators by a thin-film coating of functional polymers. We also evaluate the physical and electrochemical characteristics of these separators which are better than or compatible to the commercial separators.

Solvent Vapor Strengthened Polyimide Nanofiber-Based Aerogels with High Resilience and Controllable Porous Structure.

Owing to the hierarchically three-dimensional (3D) network, ultralow density, and high porosity, nanofiber-based aerogels (NFAs) have drawn great attention recently. However, precise control of the porous structure and mechanical properties of NFAs, which have been proved to be extremely essential to the applications, still remains a major challenge. Herein, electrospun polyimide (PI) nanofibers were utilized as building blocks to construct NFAs through the solid-templating technique. The porous structure of PI nanofiber-based aerogels (PI-NFAs) could be adjusted by changing the processing parameters. By further welding the adjacent nanofibers at the contact sites with solvent vapor, high-resilience PI-NFAs were successfully prepared with comparable or higher recoverable, under compression, folding and torsion relative to other NFAs. The welded PI-NFAs showed ultralow density (minimum of 0.96 mg/cm3), high porosity (maximum of 99.93%), and tunable hierarchical structure. Therefore, this study brought a new perspective on the simple preparation of high-resilience nanofiber-based aerogels with tunable porous structures.

A flexible capacitive pressure sensor based on an electrospun polyimide nanofiber membrane

A flexible capacitive pressure sensor based on electrospun polyimide (PI) nanofiber membrane as a dielectric layer has been proposed to improve its performance including sensitivity, detection limit and response speed due to its loose structures. An electrospun PI nanofiber membrane, a commercial PI tape and a PDMS membrane as dielectric layer had been tested and diverse thicknesses of PI nanofiber membranes were explored to optimize the dielectric layer. The sensor with such a dielectric layer exhibited high sensitivity (2.204 kPa−1 at 3.5–4.1 Pa), wide scale range (0–1.388 MPa), low detection limit (3.5 Pa) and good cyclic stability (>10,000 cycles). A typical 4 × 4 sensor array could not only accurately sense corresponding force, but also identify the slide of force by monitoring dynamic capacitive changes of elements.

Fabrication of triboelectric nanogenerators based on electrospun polyimide nanofibers membrane

Surface modification of polyimides (PIs) using electrospinning would significantly improve the performance of TENGs because of the larger surface area of the electrospun friction layer. However, PIs generally have high solvent resistance, so it is complicated to convert them into nanofibers using electrospinning process. This study aims to fabricate PI nanofibers via simple, one-step electrospinning and utilize them as a friction layer of TENGs for better performance. PI nanofibers were directly electrospun from PI ink made of polyimide powder without any additional process. The effect of PI concentration on spinnability was investigated. Uniform and continuous nanofibrous structures were successfully produced at concentrations of 15 wt% and 20 wt%. Electrospun PI nanofibers were then utilized as a friction layer for TENGs. A TENG with 20 wt% produced an open circuit voltage of 753 V and a short circuit current of 10.79 μA and showed a power density of 2.61 W m−2 at a 100 MΩ load resistance. During tapping experiment of 10,000 cycles, the TENG could stably harvest electrical energy. The harvested energy from the proposed TENG is sufficient to illuminate more than 55 LEDs and drive small electronic devices, and the TENGs exhibit excellent performance as a wearable energy harvester.

Electrospun polyimide nonwovens with enhanced mechanical and thermal properties by addition of trace plasticizer

Electrospun polyimide (PI) nanofiber nonwovens with excellent mechanical and thermal performance are highly required in many applications. The addition of phosphorus-containing compounds could be used as plasticizer to achieve this purpose. Herein, different amounts of trace diphenyl phosphate (DPhP) as plasticizer are added into the PI’s precursor for electrospinning. After imidization, phosphorous-containing electrospun PI nonwovens (PI-PX) are produced. The results indicate that the addition of DPhP significantly enhanced the thermal and mechanical properties of PI-PX. PI-P0.6 (0.6 wt% DPhP) shows a T5% of 510 °C in air and 561 °C in Ar, 29 °C and 40 °C higher than those of pure PI. PI-P0.6 also shows the highest tensile strength/modulus/toughness of 44 MPa/2.0 GPa/8.5 MPa, 208 MPa/9.7 GPa/40.7 MPa, and 123 MPa/3.3 GPa/25.1 MPa, respectively, when applying different thickness determinations. In addition, PI-P0.6 also exhibited much higher puncture strength than other Li-ion battery separators. Such PI-PX composite nonwovens would be good candidates for various applications, especially for Li-ion battery separators.

Enhanced visco-elastic and rheological behavior of epoxy composites reinforced with polyimide nanofiber

High performance epoxy composites are now a days a must in several industrial applications. In the present work electrospun polyimide (PI) nanofibers with excellent thermal and mechanical properties was used as a reinforcement in epoxy matrix via a simple mechanical mixing followed by thermal curing method. Well defined electrospun nanofibers of aromatic polyimide (PI) were successfully prepared from electrospinning Poly (amic acid) (PAA) and subsequent thermal treatment. The fiber morphology was analyzed using Transmission electron microscopy (TEM) and Atomic force microscopy (AFM). PI/epoxy nanocomposites with different PI loadings were prepared using chopped PI mats. The dynamic mechanical performance of these PI/epoxy composites was investigated to determine the influence of PI fibers in reinforcing the epoxy matrix. The fracture toughness of these composites displayed a note worthy improvement of 20 % at 1 w% loaded samples and the surface of the fractured samples was investigated by Scanning electron microscope. The rheological properties of these systems show a tremendous increase in the storage and loss modulus when compared to neat systems. In addition flow models were employed to model the rheological data and the comparison was made with the experimental data.