Mechanism of splitting in Electrospinning

Electrospinning involves the vertical stretching of the liquid jet after ejection due to the electric field and the oblique stretching of the jet caused by the Coulomb force. The liquid jet emerging with excess ions along the surface ultimately leads to electrically driven instabilities leading to whipping and branching. The controlled branching and splitting can lead to the formation of polymer nanofibers with diameters ranging from tens of nanometers to microns. We demonstrate the mechanism of jet splitting generated by electrospinning of a PEO (400,000 g/mol) in a water-ethanol drop. To scrutinize the branching event and the intricate splitting, the experiments were conducted with stereo imaging from two high-speed video cameras, at up to 200,000 fps using high magnification. For strong applied electric field, the primary jet thins into a ribbon with secondary jets emanating from the highly curved sides. The filament aspect ratio depends on the strength of the applied electric field. Above a certain threshold voltage a hole nucleates at the base of the secondary jet, which expands rapidly and then splits the jet in two. We investigate how the hole nucleation and dynamics also depend on the fluid properties.