Wave propagation of bending jet in electrospinning process

The electrospinning process features bending jets in space and solidified nanofibers on a collector. Although electrospun nanofibers have been widely applied, the wave characteristics, especially the first jet bend and tapered envelope cone profile, of bending jets are not fully comprehended. In this work, a spatial normal mode k− is true to characterize the convective instability of a bending jet. Some real wave variables are measured and calculated. It is observed that the first jet bend occurs at the jet end. The instability grows quickly at the early stage of a wave. Underdeveloped dispersive waves are temporally and spatially unstable. When dispersive waves develop to a mature stage, the instability grows slowly, and developed dispersive waves are only spatially unstable. Furthermore, the energy ratio of electric energy to kinematic energy accounts for the wave characteristics of a bending jet. A high energy ratio may stabilize the jet, and a very low energy ratio destabilizes the jet. The stabilizing effect of the high energy ratio suppresses the growth of dispersive waves at the jet source. Once residual charges within the jet trigger small perturbations to the electric field near the plate owing to the Coulomb repulsive effect of like charges, the destabilizing effect of the low energy ratio causes the rapid development of small perturbation first at the jet end. The inhomogeneous distribution of electric energy contributes to the tapered envelope cone profile of a bending jet. Numerically and experimentally, the wave speed is in the order of 1 m/s, and the growth rate is in the order of 102 m−1. The numerical results are in accordance with the experimental results.