Controlling instabilities of electrified liquid jets via orthogonal perturbations

Whipping is a peculiar nonaxisymmetric instability experienced by electrified liquid jets and utilized in electrospinning to produce fine polymer fibers; however, it manifests itself in a chaotic and uncontrollable fashion. We impose two perturbations in the form of small mechanical oscillations, orthogonal with each other, to alter and curb instabilities of electrified liquid jets. The oscillations cause transverse positioning disturbance to the nozzle and therefore the initial positioning of the jet. The effects of parameters including the excitation frequency, amplitude, and phase difference of the imposed perturbations and the axial electric field are investigated. The steady helicoidal whipping structure with a linearly growing lateral amplitude in air has been demonstrated, offering a feasible solution for electrospinning to fabricate fibers of uniform thickness. Furthermore, the superposition of two sinusoidal orthogonal perturbations enables deposition of complex patterns, such as Lissajous curves.