Electrospinning uses an electrical charge to draw very fine (typically on the micro
or nano scale) fibres from a liquid. Electrospinning shares characteristics of both
electrospraying and conventional solution dry spinning of fibers. The process does
not require the use of coagulation chemistry or high temperatures to produce solid
threads from solution. This makes the process particularly suited to the production
of fibers using large and complex molecules. Electrospinning from molten precursors
is also practised; this method ensures that no solvent can be carried over into
the final product.
When a sufficiently high voltage is applied to a liquid droplet, the body of the
liquid becomes charged, and electrostatic repulsion counteracts the surface tension
and the droplet is stretched; at a critical point a stream of liquid erupts from
the surface. This point of eruption is known as the Taylor cone. If the molecular
cohesion of the liquid is sufficiently high, stream breakup does not occur (if it
does, droplets are electrosprayed) and a charged liquid jet is formed. As the jet
dries in flight, the mode of current flow changes from ohmic to convective as the
charge migrates to the surface of the fiber. The jet is then elongated by a whipping
process caused by electrostatic repulsion initiated at small bends in the fiber,
until it is finally deposited on the grounded collector. The elongation and thinning
of the fiber resulting from this bending instability leads to the formation of uniform
fibers with nanometer-scale diameters.