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1. Electrospun Conducting Polymers: Approaches and Applications

   https://doi.org/10.3390/ma15248820  

   Acosta, Mariana; Santiago, Marvin D.; Irvin, Jennifer A. (December 2022, Materials)

   Inherently conductive polymers (CPs) can generally be switched between two or more stable oxidation states, giving rise to changes in properties including conductivity, color, and volume. The ability to prepare CP nanofibers could lead to applications including water purification, sensors, separations, nerve regeneration, wound healing, wearable electronic devices, and flexible energy storage. Electrospinning is a relatively inexpensive, simple process that is used to produce polymer nanofibers from solution. The nanofibers have many desirable qualities including high surface area per unit mass, high porosity, and low weight. Unfortunately, the low molecular weight and rigid rod nature of most CPs cannot yield enough chain entanglement for electrospinning, instead yielding polymer nanoparticles via an electrospraying process. Common workarounds include co-extruding with an insulating carrier polymer, coaxial electrospinning, and coating insulating electrospun polymer nanofibers with CPs. This review explores the benefits and drawbacks of these methods, as well as the use of these materials in sensing, biomedical, electronic, separation, purification, and energy conversion and storage applications. 

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2. A Review on Electrospun Luminescent Nanofibers: Photoluminescence Characteristics and Potential Applications

   https://doi.org/10.2174/1573413715666190112121113  

   George, Gibin; Luo, Zhiping (April 2020, Current Nanoscience)

   Background: Photoluminescent materials have been used for diverse applications in thefields of science and engineering, such as optical storage, biological labeling, noninvasive imaging,solid-state lasers, light-emitting diodes, theranostics/theragnostics, up-conversion lasers, solar cells,spectrum modifiers, photodynamic therapy remote controllers, optical waveguide amplifiers andtemperature sensors. Nanosized luminescent materials could be ideal candidates in these applications.Objective: This review is to present a brief overview of photoluminescent nanofibers obtainedthrough electrospinning and their emission characteristics.Methods: To prepare bulk-scale nanosized materials efficiently and cost-effectively, electrospinningis a widely used technique. By the electrospinning method, a sufficiently high direct-current voltageis applied to a polymer solution or melt; and at a certain critical point when the electrostatic forceovercomes the surface tension, the droplet is stretched to form nanofibers. Polymer solutions or meltswith a high degree of molecular cohesion due to intermolecular interactions are the feedstock. Subsequentcalcination in air or specific gas may be required to remove the organic elements to obtainthe desired composition.Results: The luminescent nanofibers are classified based on the composition, structure, and synthesismaterial. The photoluminescent emission characteristics of the nanofibers reveal intriguing featuressuch as polarized emission, energy transfer, fluorescent quenching, and sensing. An overview of theprocess, controlling parameters and techniques associated with electrospinning of organic, inorganicand composite nanofibers are discussed in detail. The scope and potential applications of these luminescentfibers also conversed.Conclusion: The electrospinning process is a matured technique to produce nanofibers on a largescale. Organic nanofibers have exhibited superior fluorescent emissions for waveguides, LEDs andlasing devices, and inorganic nanofibers for high-end sensors, scintillators, and catalysts. Multifunctionalitiescan be achieved for photovoltaics, sensing, drug delivery, magnetism, catalysis, andso on. The potential of these nanofibers can be extended but not limited to smart clothing, tissueengineering, energy harvesting, energy storage, communication, safe data storage, etc. and it isanticipated that in the near future, luminescent nanofibers will find many more applications in diversescientific disciplines. 

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3. Recent progress in electrospun nanomaterials for wearables

   https://doi.org/10.1063/5.0088136  

   Das, Riddha; Zeng, Wenxin; Asci, Cihan; Del-Rio-Ruiz, Ruben; Sonkusale, Sameer (June 2022, APL Bioengineering)

   Wearables have garnered significant attention in recent years not only as consumer electronics for entertainment, communications, and commerce but also for real-time continuous health monitoring. This has been spurred by advances in flexible sensors, transistors, energy storage, and harvesting devices to replace the traditional, bulky, and rigid electronic devices. However, engineering smart wearables that can seamlessly integrate with the human body is a daunting task. Some of the key material attributes that are challenging to meet are skin conformability, breathability, and biocompatibility while providing tunability of its mechanical, electrical, and chemical properties. Electrospinning has emerged as a versatile platform that can potentially address these challenges by fabricating nanofibers with tunable properties from a polymer base. In this article, we review advances in wearable electronic devices and systems that are developed using electrospinning. We cover various applications in multiple fields including healthcare, biomedicine, and energy. We review the ability to tune the electrical, physiochemical, and mechanical properties of the nanofibers underlying these applications and illustrate strategies that enable integration of these nanofibers with human skin. 

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4. Shear Force Fiber Spinning: Process Parameter and Polymer Solution Property Considerations

   https://doi.org/10.3390/polym11020294  

   Dotivala, Arzan; Puthuveetil, Kavya; Tang, Christina (February 2019, Polymers)

   For application of polymer nanofibers (e.g., sensors, and scaffolds to study cell behavior) it is important to control the spatial orientation of the fibers. We compare the ability to align and pattern fibers using shear force fiber spinning, i.e. contacting a drop of polymer solution with a rotating collector to mechanically draw a fiber, with electrospinning onto a rotating drum. Using polystyrene as a model system, we observe that the fiber spacing using shear force fiber spinning was more uniform than electrospinning with the rotating drum with relative standard deviations of 18% and 39%, respectively. Importantly, the approaches are complementary as the fiber spacing achieved using electrospinning with the rotating drum was ~10 microns while fiber spacing achieved using shear force fiber spinning was ~250 microns. To expand to additional polymer systems, we use polymer entanglement and capillary number. Solution properties that favor large capillary numbers (>50) prevent droplet breakup to facilitate fiber formation. Draw-down ratio was useful for determining appropriate process conditions (flow rate, rotational speed of the collector) to achieve continuous formation of fibers. These rules of thumb for considering the polymer solution properties and process parameters are expected to expand use of this platform for creating hierarchical structures of multiple fiber layers for cell scaffolds and additional applications. 

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5. Novel Wet Electrospinning Inside a Reactive Pre-Ceramic Gel to Yield Advanced Nanofiber-Reinforced Geopolymer Composites

   https://doi.org/10.3390/polym14193943  

   Xu, Yunzhi; Guo, Ping; Akono, Ange-Therese (October 2022, Polymers)

   Electrospinning is a versatile approach to generate nanofibers in situ. Yet, recently, wet electrospinning has been introduced as a more efficient way to deposit isolated fibers inside bulk materials. In wet electrospinning, a liquid bath is adopted, instead of a solid collector, for fiber collection. However, despite several studies focused on wet electrospinning to yield polymer composites, few studies have investigated wet electrospinning to yield ceramic composites. In this paper, we propose a novel in-situ fabrication approach for nanofiber-reinforced ceramic composites based on an enhanced wet-electrospinning method. Our method uses electrospinning to draw polymer nanofibers directly into a reactive pre-ceramic gel, which is later activated to yield advanced nanofiber-reinforced ceramic composites. We demonstrate our method by investigating wet electrospun Polyacrylonitrile and Poly(ethylene oxide) fiber-reinforced geopolymer composites, with fiber weight fractions in the range 0.1–1.0 wt%. Wet electrospinning preserves the amorphous structure of geopolymer while changing the molecular arrangement. Wet electrospinning leads to an increase in both the fraction of mesopores and the overall porosity of geopolymer composites. The indentation modulus is in the range 6.76–8.90 GPa and the fracture toughness is in the range 0.49–0.76 MPam with a clear stiffening and toughening effect observed for Poly(ethylene oxide)-reinforced geopolymer composites. This work demonstrates the viability of wet electrospinning to fabricate multifunctional nanofiber-reinforced composites. 

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