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Lesson 13.9Micro & nanoChapter 13 · Micro- and nanofabrication

Electrospinning

Pulls a polymer jet into nanofibers with high voltage

Electrospinning uses a high voltage to pull a polymer solution into fibers hundreds of times thinner than a hair. The fibers pile up as a light, airy web called a nanofiber mat. Such mats boost air filters and face masks, and serve as scaffolds for growing tissue.

Electrospinning: a real photo
Photo: Farizat Aidyn, CC BY-SA 4.0, via Wikimedia Commons
High voltage pulls a polymer drop into a jet that dries into nanofibersElectrospinning · side view, not to scaleSyringe pump21polymer solutionmetal needle3High voltage5–50 kVstraight jetwhipping jetstretches, dries4grounded collectorgroundnanofiber mat5Taylor cone at the needle tipcharges pull the drop into a pointneedleTaylor conejetchargesThe web, magnifiedeach thin line is one fibera human hair, about 70 µm thickPolymer solutionFiber (the product)Machine partsHigh voltage
electrospinning · set-up, Taylor cone zoom and fiber webCircled numbers match the steps below; the two framed panels zoom in on the needle tip and on the finished web.

How it works

  1. Prepare the solution. A polymer is dissolved in a solvent, or melted, to the right viscosity (how thick and slow-flowing a liquid is).

  2. Feed a droplet. A syringe pump pushes the solution slowly to the tip of a metal needle, where a droplet hangs.

  3. Apply high voltage. A supply of typically 5 to 50 kilovolts charges the droplet. Electric forces overcome surface tension and pull the drop into a point called a Taylor cone.

  4. Jet and whip. A fine jet shoots from the cone tip, then spirals and whips wildly. It stretches thousands of times while the solvent evaporates.

  5. Collect the fibers. Dry fibers land on a grounded collector: a flat plate for a random web, a fast-spinning drum for aligned fibers, or a moving fabric in a factory. The mat is then peeled off, laminated onto a support or sterilized for medical use.

Key facts

Materials
Polymer solutions or melts: nylon, polyester (PET), PVDF, PAN, biodegradable PCL, PVA, collagen, cellulose acetate; also ceramic precursors
Typical parts
Nonwoven (felt-like, not woven) fiber mats, filter layers on fabrics, tubes, aligned yarns
Part size
Fibers from tens of nanometers to a few microns thick; mats from lab samples to industrial rolls meters wide
Precision
No dimensional tolerance as such: the recipe and settings control fiber diameter and its spread
Surface finish
Soft, felt-like web with a huge surface area and fine pores that trap sub-micron particles
Batch size it suits
Lab grams to roll-to-roll production lines meters wide
Tooling and machine cost
Lab set-up from a few thousand dollars; industrial lines much more
Speed
A single needle makes well under a gram of fiber per hour; needleless factory lines coat fabric continuously

Strengths and limits

Strengths

  • Ultra-fine fibers with a huge surface area
  • Simple, low-cost lab set-up
  • Huge choice of polymers, blends and additives (drugs, particles)
  • Mimics the fiber network around body cells, which helps cells grow

Limits

  • Low output from single needles
  • Many recipes use toxic or flammable solvents
  • Fiber size drifts with humidity, voltage and distance
  • Weak mats usually need a support layer; high-voltage safety rules apply

Where it's used

  • FiltrationNanofiber layers in building ventilation, engine air and face-mask filters
  • MedicalWound dressings, tissue-engineering scaffolds, vascular grafts, drug-release patches
  • EnergyBattery separators, fuel-cell membranes
  • TextilesBreathable waterproof membranes, protective clothing
  • CosmeticsNanofiber face masks and patches
  • ResearchSensors, catalysts, ceramic nanofibers

How to recognize it

  • Single fibers are invisible to the eye; only the web shows, as a whisper-thin white or translucent film.
  • Look at some high-efficiency air, vacuum or engine filters: a delicate coating on a coarser fabric that seems too light to work.
  • Under an electron microscope the web looks like tangled spaghetti, with strands of nearly the same thickness.
  • Medical versions end up on wounds or inside the body, as dressings and scaffolds that may slowly dissolve.

Compare with

Extrusion3.3pushes material through a shaped die opening; it makes ordinary fibers and profiles, far thicker and faster.Wire drawing3.4thins solid metal wire by pulling it through dies; electrospinning thins a liquid jet with electric forces instead.Two-photon polymerization13.8places every micro-feature exactly; electrospinning makes a random web, cheaply, with little control over where each fiber lands.

Watch it

Hosein Rostamani · A simple lab walkthrough from solution to fiber mat

Inovenso Ltd. Electrospinning Company · Close-up of the Taylor cone and jet at one nozzle

ELMARCO · Industrial needleless jets rising from a rotating drum

Foshan MBRT Nanofiberlabs Co.,Ltd · An overview of nanofiber products and uses

See real photos

Remember

  • Electric force does the stretching: drop, cone, whipping jet, dry fiber.
  • Fibers are tens of nanometers to a few microns thick, and the web has a huge surface area.
  • Single needles are slow; factories use needleless lines to coat filter fabrics.

More in Micro- and nanofabrication

All 100 processes
13.1Czochralski crystal growth (silicon wafers)Pulls a giant single crystal of silicon slowly out of a meltOpen the lesson13.2PhotolithographyProjects a pattern with light onto a light-sensitive coating, then etches itOpen the lesson13.3Molecular beam epitaxy (MBE)Grows a crystal one atomic layer at a time from beams in ultra-high vacuumOpen the lesson13.4Atomic layer deposition (ALD)Coats a surface one atomic layer per cycle with alternating gasesOpen the lesson13.5Focused ion beam (FIB)Mills or adds material with a beam of ions under a microscopeOpen the lesson13.6Femtosecond laser machiningRemoves material with ultrashort laser pulses, without meltingOpen the lesson13.7LIGADraws deep slots with X-rays or UV, fills them with nickel, then molds copiesOpen the lesson13.8Two-photon polymerizationHardens resin only at a laser focus to print 3D micro-partsOpen the lesson

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