by Dr Nick Tucker, School of Engineering, College of Science, University of Lincoln, Lincoln, UK.
Electrospinning is a well-established industrial method of making nano-scale polymer fibres. The fibre is drawn from a droplet of material by electrostatic attraction, and rapidly accelerates towards the nearest earthed surface – often the collection surface. The flight path of the fibre is initially straight but at a certain point, curves into a spiral. This so-called instability makes it tricky to control the deposition pattern of fibres: the fibre mat has the appearance of random deposition. There are methods of improving control over the deposition pattern for example by collecting the fibre on a rotating mandrel or a “window frame” electrode, but the presence of the instability is a continuing problem in controlling the flight path.
It is possible that the onset of the instability is due to the fibre reaching its terminal velocity, and then buckling under compressive load. Work is progressing to test this hypothesis by spinning the fibre in reduced air pressure and ultimately in a vacuum. Preliminary results support the hypothesis. If the flight path can be straightened out, then it is likely that the deposition pattern can be controlled by varying the electrostatic field through which the flight path passes.