1. What electrospinning and nanofibers are, in three points

• What it does: In 1996 Reneker and Chun described electrospinning as using electrical forces to produce polymer fibres with nanometre-scale diameters. When the electrical forces at the surface of a solution or melt overcome the surface tension, an electrically charged jet is ejected, and when the jet dries or solidifies a charged fibre remains Sourced
• How fine: The review by Greiner and Wendorff describes a method that makes continuous fibres from a few micrometres down to a few nanometres in diameter and applies to virtually every soluble or fusible polymer Sourced. Note that even when called “nanofibers”, actual diameters range from a few nanometres to several micrometres (Chapter 12)
• What is hard: The small output of a single nozzle (typically around 0.01–1 g per hour, according to a review), making the diameter uniform, and the amount and toxicity of solvent Sourced (Chapters 10 and 11)

2. Principle: drawing a fibre with high voltage

(1) A short history

Drawing threads from a liquid with electrical force is an old idea. A 1934 US patent (A. Formhals) states that the action of an electrical field on liquids containing dissolved material, to form threads, was already known, identifies as its problem that the threads could not be removed in a technically useful form, and proposes a design in which a movable, conducting collecting device (a reel, spool or drum) also acts as the electrode that attracts the threads Sourced. The ancestor of today's drum collector is thus in a patent more than 90 years old. In 1996 Reneker and Chun reported spinning more than 20 polymers, including polyethylene oxide, nylon, polyimide, DNA, polyaramid and polyaniline, mostly from solution but also from the melt in vacuum and in air Sourced.

(2) The jet forms, bends and thins

The process can be organised in the following stages (drawing on the papers of Reneker et al. and Taylor and on the reviews).

1. The Taylor cone: The drop at the nozzle tip is stretched into a cone by the electric field. In a 1964 paper Taylor showed, by theory and experiment, that a drop elongated by an electric field becomes unstable when its length is 1.9 times its equatorial diameter, and that a conical interface between two fluids can exist in equilibrium in an electric field only when the cone has a semi-vertical angle of 49.3° Sourced (Taylor's paper dealt with the disintegration of water drops in electric fields, not with spinning polymer solutions as such).
2. The straight jet: The jet ejected from the tip of the cone travels in a nearly straight line for some distance. In the mathematical model of Reneker et al., the longitudinal stress caused by the external electric field acting on the charge carried by the jet stabilises the straight jet for that distance Sourced.
3. The bending instability: Then a lateral perturbation grows in response to the repulsive forces between adjacent elements of charge on the jet, and an electrically driven bending instability takes over. The jet follows a complex path and is stretched and thinned by very large ratios by electrical forces. After the solvent evaporates, birefringent nanofibers remain Sourced.
4. Solidification and deposition: When the solvent evaporates or the melt cools, a charged fibre remains and is directed by electrical forces onto a collector Sourced.

View the original SVG schematic and exact annotations

Reading guide and original schematic labels: Principle of electrospinning (concept) / syringe / collector (grounded; drum or plate) / high-voltage supply (+) / Taylor cone / straight part / bending / instability / 1. Taylor cone / The field draws the drop into a cone. / Equilibrium cone: 49.3° semi-angle (Taylor) / 2. Straight jet / Leaves the tip and runs nearly straight / 3. Bending instability / Charge repulsion makes it whip sideways, / and the jet is stretched enormously / 4. Solidification / Solvent evaporates (or the melt cools) / 5. Deposition / Fibres gather on the collector as a mat / Note: conceptual; no voltages, distances or jet diameters are shown. Based on the papers of Taylor and Reneker et al. [Ref. 2, 4].

3. What sets fibre diameter: our calculation

Fibre thickness depends not only on equipment settings (voltage, flow rate, distance) but strongly on how the polymer chains in the solution are entangled. McKee et al. studied linear and branched poly(ethylene terephthalate-co-ethylene isophthalate) (PET-co-PEI) copolymers with weight-average molecular weights of 11,700 to 106,000 g/mol, relating the concentration regime of the solution (semidilute unentangled, semidilute entangled, concentrated) to the morphology of the fibres spun from it Sourced.

• For copolymers whose molecular weight is well above the entanglement molecular weight, the entanglement concentration C_e was the minimum concentration for electrospinning beaded fibres
• For uniform, bead-free fibres, 2–2.5 times C_e was the minimum concentration
• When concentration was normalised by C_e, the influence of chain length and topology disappeared, and fibre diameter scaled with the normalised concentration (C/C_e) to the power 2.6

4. A materials engineer's view (1): thickness is set by entanglement, not by concentration

5. Equipment: nozzle, collector and free surface

The basic equipment has three parts: (1) the part that feeds the solution (syringe and pump, nozzle), (2) a high-voltage supply, and (3) the collector that receives the fibre. The review by Xue et al. organises the principle and typical apparatus of electrospinning, its methods, materials and applications, and approaches to scale-up Sourced. Here the configurations are divided into three.

(1) Needle (nozzle) type, and different collectors

The most basic arrangement ejects one jet from one nozzle and gathers it on a plate or a rotating drum. The shape of the collector sets how the fibres lie. Li, Wang and Xia reported that using as collector two conducting substrates separated by a gap makes the charged fibres stretch across the gap by electrostatic interactions and form uniaxially aligned arrays over large areas, with success for organic polymers, ceramics and composites Sourced. Theron et al. reported winding fibre onto a pointed, grounded rotating bobbin to lay polyethylene oxide fibres of 100–300 nm diameter in parallel Sourced.

(2) Coaxial nozzle (core–shell, hollow)

In 2003 Sun et al. introduced co-electrospinning: a spinnable polymer as the outer shell and a non-spinnable material as the core are extruded coaxially to form two-layer fibres. Materials that cannot be spun alone can thus be forced into one-dimensional arrangements, and nanotubes can be made in two stages instead of three, they state Sourced. In 2004 Li and Xia spun two immiscible liquids through a two-capillary spinneret and removed the core afterwards to leave hollow nanofibers (titania/polymer composites, anatase nanotubes). They state that a sol–gel precursor in the sheath liquid was necessary for stable coaxial jets and robust walls Sourced.

(3) The free-surface type, without needles

US Patent 7,585,437 B2 of Jirsak et al. (applicant: Technical University of Liberec; PCT application 8 September 2004; granted 8 September 2009) describes a method and device in which part of the circumference of a rotating charged electrode is immersed in the polymer solution, and the solution is supplied into the electric field on the surface of the electrode to attain a high spinning capacity Sourced. The review by Omer et al. describes the formation of multiple jets from the surface of a polymer solution with a charged cylindrical electrode as the first patent on this technology, followed by the world's first industrial free-surface set-up, Nanospider™ from Elmarco Sourced. We have not confirmed whether the review's first patent is the Jirsak patent above. Elmarco's own web page describes Nanospider™ as an electrospinning method using the free surface of a polymer-solution-coated electrode in a strong electrostatic field, using a thin wire electrode, with a design that allows up to four spinning units to be assembled in one industrial line (the manufacturer's description) Sourced. The chapter by Wen and Wang classifies strategies for mass production into multiple-needle, multiple-hole, free-surface, melt and multifield-assisted electrospinning Sourced.

6. Materials: polymers and ceramic precursors

(1) Polymers

The review by Greiner and Wendorff says electrospinning can be applied to virtually every soluble or fusible polymer, and that polymers can be given additives ranging from simple carbon-black particles to complex species such as enzymes, viruses and bacteria Sourced. Reneker and Chun reported spinning from solution and also from the melt in vacuum, noting that melt spinning in vacuum allows higher fields and higher temperatures than in air Sourced.

(2) Ceramics come from “precursor plus carrier polymer”

Ceramic nanofibers are made by spinning a solution that mixes a precursor with a polymer that helps spinning, and then firing to remove the polymer. In the 2003 report of Li and Xia, an ethanol solution containing PVP (poly(vinyl pyrrolidone), M_w ≈ 1,300,000) and titanium tetraisopropoxide was injected through a needle under a strong electric field and gave composite nanofibers of PVP and amorphous TiO₂ (up to several centimetres long). Calcination in air at 500 °C converted them to anatase without changing their morphology, and the average diameter could be controlled from 20 to 200 nm by the PVP-to-precursor ratio, the concentrations, the field strength and the feed rate Sourced.

View the original SVG schematic and exact annotations

Reading guide and original schematic labels: How ceramic nanofibers are made (TiO₂ example) / 1. Precursor soln. / ethanol / + PVP (carrier) / + Ti alkoxide / 2. Electrospinning / jet ejected from a / needle in a strong / electric field / 3. Composite fibre / PVP + amorphous / TiO₂ (up to / several cm long) / 4. Calcination / in air, 500 °C / removes PVP, / crystallises / 5. Product / anatase / nanofibers / 20-200 nm / For hollow fibres (coaxial spinning) / A sol-gel precursor in the sheath and an immiscible liquid in the core are extruded from a coaxial nozzle; / after spinning, the core is removed, leaving titania/polymer composite nanotubes or anatase nanotubes (Li and Xia 2004) / Commentary: the carrier polymer helps spinning and is removed during calcination (system of Li and Xia, 2003) / Note: conceptual. The numbers apply only to the system of Li and Xia 2003 [Ref. 9] / (PVP + titanium tetraisopropoxide, 500 °C calcination), not to other materials. / It does not depict the full conditions of a real instrument or process.

7. A materials engineer's view (2): what was “nanofiber diameter” measured with?

8. Uses: filters, battery separators and medicine

(1) Air filters

The review by Lyu et al. says that filter membranes are evaluated by a quality factor (QF), and a membrane with a high QF must have both high filtration efficiency and low pressure drop. As features of electrospun membranes it lists a low Knudsen number, slip flow that lowers pressure drop and garland-like structures that raise capture efficiency, and organises structures such as bead-on-string and multilayer designs as ways to optimise performance Sourced. The review includes example values: a PA-6 membrane (needle-free spinning with a spiral electrode) with PM filtration efficiency of 99.42% and pressure drop of 85.5 Pa; a PAN bead-on-string membrane above 99% at 27 Pa; and a GO-PAN composite membrane at 99.97% and 8 Pa Sourced. These come from different papers, and whether particle size, face velocity and test method are the same could not be confirmed, either in the review or in this article. They should not be set side by side to rank them.

(2) Battery separators

The review by Arora and Zhang says the ideal battery separator would be infinitesimally thin, offer no resistance to ionic transport in electrolytes, provide infinite resistance to electronic conductivity, be highly tortuous to prevent dendritic growth, and be inert to chemical reactions; in the real world this does not exist, and compromises are made by manipulating thickness and porosity Sourced. The review by Li et al. calls electrospun nonwovens a promising candidate for lithium-ion battery separators because of their interconnected porous structures, high porosities and large surface-to-volume ratio, and classifies them into five types: monolayer, multilayer, modified, composite and gel polymer electrolyte Sourced. What can be said here goes only as far as organising research; to what extent electrospun nonwovens are used in commercial batteries could not be confirmed in primary sources in this article.

(3) Medical uses

The review by Agarwal et al. describes electrospinning as a technique that gives nonwovens with fibres down to a few nanometres, large surface areas and ease of functionalisation, used in tissue engineering, drug release, wound dressing, enzyme immobilisation and similar Sourced. The review by Omer et al. lists as problems the toxicity of residual organic solvent and variation in properties between batches for natural polymers such as silk fibroin Sourced. The effect, safety and approval status of individual medical products must be confirmed product by product in official documents; this article does not evaluate them.

9. A materials engineer's view (3): each use wants a different fibre

10. Volume production and its problems: uniformity and solvent

(1) Scale of output

The review by Omer et al. says typical electrospinning output is around 0.01–1 g per hour, too low for pharmaceutical requirements, and compares routes to volume production such as multiple needles, free-surface (needle-free) methods and centrifugal approaches. It says needleless and centrifugal methods have gained the most attention, with output reaching 450 g per hour in some cases Sourced. The same review cites laboratory free-surface examples of 8.6 g/h (cylinder), 6.2 g/h (disk) and 3.1 g/h (ball) for PVA fibres, 13.7 g/h for another method, about 80 g/h for a 36-orifice high-speed spinner, and for Nanospider™ 1.5 g per minute per metre of roller length with fibre diameters of 50–500 nm (each quoted from separate papers or manufacturer material) Sourced.

(2) The uniformity problem

The review by Persano et al. says that electrospinning equipment, technological solutions and materials are rapidly moving to commercialisation, and analyses the technological approaches that promise scale-up that fulfils industrial requirements for throughput, accuracy and functionality Sourced. The review by Omer et al. lists, as quality problems, variation between batches of natural polymers, toxicity from residual organic solvent, stability of active agents under heat treatment, and the fact that the process is relatively slow and time-consuming Sourced. Uniformity will be managed as the distribution of fibre diameter and basis weight across the width, the fraction of defects such as beads, and lot-to-lot reproducibility (Commentary; this article has not confirmed concrete specification or control values).

11. A materials engineer's view (4): how many times the fibre's mass is the solvent?

12. “Nanofiber” versus the EU's “nanomaterial”

The name “nanofiber” and the legal term “nanomaterial” are not the same thing. Greiner and Wendorff give electrospun fibre diameters as a few micrometres down to a few nanometres, and many products called “nanofibers” exceed 100 nm (including the 150 nm of the example above) Sourced.

The Commission Recommendation of 10 June 2022 (2022/C 229/01) defines a nanomaterial as a material consisting of solid particles, where 50% or more of the particles in the number-based size distribution fulfil at least one of the following conditions: (a) one or more external dimensions of the particle are in the range 1 nm to 100 nm; (b) the particle has an elongated shape, such as a rod, fibre or tube, where two external dimensions are smaller than 1 nm and the other is larger than 100 nm; (c) the particle has a plate-like shape, where one external dimension is smaller than 1 nm and the other dimensions are larger than 100 nm. It further provides that a material with a specific surface area by volume of less than 6 m²/cm³ shall not be considered a nanomaterial Sourced.

• A fibre of 100 nm diameter or less can meet condition (a), but a fibre of 150 nm falls outside the 1–100 nm range in diameter. What counts is whether particles of 100 nm or less make up 50% or more of the number-based distribution (our reading).
• The volume-specific surface area of a cylinder is 4 ÷ diameter, which reaches 6 m²/cm³ at a diameter of 667 nm (Fig. 2) Our calculation. This is a reference value converting the recommendation's exclusion threshold by cylinder geometry alone, and does not indicate how a nonwoven product is treated under regulation.
• This recommendation is a recommended definition for EU policy and legislative use; its treatment under individual laws (REACH, cosmetics, food and so on) has to be checked law by law. How a formed article such as a nonwoven fits the recommendation's “material” and “particle” could not be confirmed in this article Not yet confirmed

13. What this article could not confirm, and a summary

14. Glossary

15. References (primary sources)

1. Formhals A US Patent 1,975,504, Process and apparatus for preparing artificial threads (2 October 1934) — patents.google.com
2. Taylor G Disintegration of water drops in an electric field. Proc R Soc Lond A 1964;280:383–397 — doi.org/10.1098/rspa.1964.0151
3. Reneker DH, Chun I Nanometre diameter fibres of polymer, produced by electrospinning. Nanotechnology 1996;7:216–223 — doi.org/10.1088/0957-4484/7/3/009
4. Reneker DH et al. Bending instability of electrically charged liquid jets of polymer solutions in electrospinning. J Appl Phys 2000;87:4531–4547 — doi.org/10.1063/1.373532
5. Greiner A, Wendorff JH Electrospinning: A Fascinating Method for the Preparation of Ultrathin Fibers. Angew Chem Int Ed 2007;46:5670–5703 — doi.org/10.1002/anie.200604646
6. Li D, Xia Y Electrospinning of Nanofibers: Reinventing the Wheel? Adv Mater 2004;16:1151–1170 — doi.org/10.1002/adma.200400719
7. Xue J et al. Electrospinning and Electrospun Nanofibers: Methods, Materials, and Applications. Chem Rev 2019;119:5298–5415 — doi.org/10.1021/acs.chemrev.8b00593
8. McKee MG et al. Correlations of Solution Rheology with Electrospun Fiber Formation of Linear and Branched Polyesters. Macromolecules 2004;37:1760–1767 — doi.org/10.1021/ma035689h
9. Li D, Xia Y Fabrication of Titania Nanofibers by Electrospinning. Nano Lett 2003;3:555–560 — doi.org/10.1021/nl034039o
10. Li D, Xia Y Direct Fabrication of Composite and Ceramic Hollow Nanofibers by Electrospinning. Nano Lett 2004;4:933–938 — doi.org/10.1021/nl049590f
11. Sun Z et al. Compound Core–Shell Polymer Nanofibers by Co-Electrospinning. Adv Mater 2003;15:1929–1932 — doi.org/10.1002/adma.200305136
12. Li D, Wang Y, Xia Y Electrospinning of Polymeric and Ceramic Nanofibers as Uniaxially Aligned Arrays. Nano Lett 2003;3:1167–1171 — doi.org/10.1021/nl0344256
13. Jirsak O et al. (Technicka Univerzita v Liberci) US Patent 7,585,437 B2, Method of nanofibres production from a polymer solution using electrostatic spinning and a device for carrying out the method (filed 8 September 2004; granted 8 September 2009) — patents.google.com
14. Elmarco Nanospider technology (the manufacturer's web page) — elmarco.com
15. Persano L et al. Industrial Upscaling of Electrospinning and Applications of Polymer Nanofibers: A Review. Macromol Mater Eng 2013;298:504–520 — doi.org/10.1002/mame.201200290
16. Omer S et al. Scale-up of Electrospinning: Market Overview of Products and Devices for Pharmaceutical and Biomedical Purposes. Pharmaceutics 2021;13:286 — doi.org/10.3390/pharmaceutics13020286
17. Wen X, Wang L Mass Production of Electrospun Nanofibers. In: Electrospinning, Wiley 2024, pp. 29–43 — doi.org/10.1002/9783527841479.ch3
18. Lyu C et al. Electrospinning of Nanofibrous Membrane and Its Applications in Air Filtration: A Review. Nanomaterials 2021;11:1501 — doi.org/10.3390/nano11061501
19. Li Y, Li Q, Tan Z A review of electrospun nanofiber-based separators for rechargeable lithium-ion batteries. J Power Sources 2019;443:227262 — doi.org/10.1016/j.jpowsour.2019.227262
20. Arora P, Zhang Z Battery Separators. Chem Rev 2004;104:4419–4462 — doi.org/10.1021/cr020738u
21. Agarwal S, Wendorff JH, Greiner A Use of electrospinning technique for biomedical applications. Polymer 2008;49:5603–5621 — doi.org/10.1016/j.polymer.2008.09.014
22. Liverani L, Boccaccini AR Versatile Production of Poly(Epsilon-Caprolactone) Fibers by Electrospinning Using Benign Solvents. Nanomaterials 2016;6:75 — doi.org/10.3390/nano6040075
23. Avossa J et al. Electrospinning based on benign solvents: current definitions, implications and strategies. Green Chem 2022;24:2347–2375 — doi.org/10.1039/d1gc04252a
24. Hotaling NA et al. DiameterJ: A validated open source nanofiber diameter measurement tool. Biomaterials 2015;61:327–338 — doi.org/10.1016/j.biomaterials.2015.05.015
25. European Commission Commission Recommendation of 10 June 2022 on the definition of nanomaterial (2022/C 229/01; Official Journal C 229/1, 14 June 2022) — eur-lex.europa.eu
26. Theron A, Zussman E, Yarin AL Electrostatic field-assisted alignment of electrospun nanofibres. Nanotechnology 2001;12:384–390 — doi.org/10.1088/0957-4484/12/3/329

16. Claim-to-source audit

Last updated October 2026. Sources are limited to primary material (peer-reviewed papers, patent specifications, a manufacturer's own web page and a European Commission recommendation). The Nanospider™ figures (basis weight, fibre diameter, annual output and so on) are quoted by the review of Omer et al. from manufacturer material and could not be confirmed on the manufacturer's own web page. The output figures come from reports under differing conditions and do not rank methods. Because the article includes structural readings and materials-design interpretations, those are marked as Commentary and kept separate from sourced fact. The details of the manufacturer's figures (the meaning of ±30%), the treatment of solvents such as DMF under REACH, the numbers of ISO standards on nanofibers, the treatment of formed articles under the EU recommendation, and the use of electrospun separators in commercial batteries are not covered, because they could not be confirmed in primary sources. This article explains materials, principles and processes. It does not rank any product or company, and it is not medical or safety advice. The hero image and Fig. 7 are AI-generated images and the other figures are vector drawings; none of them shows a real instrument, product or measurement result.