Axisymmetric instabilities of electrically driven viscoelastic jets

A theoretical and experimental investigation of the axisymmetric stability of electrically driven viscoelastic jets observed during electrospinning is presented. In the theoretical study, a linear stability analysis for the emergence of axisymmetric instability is coupled with a model for the development of the 'stable jet' in electrospinning. The Oldroyd-B fluid model is used to account for the non-Newtonian viscoelastic behavior of the polymer solutions that are electrospun. The simulation predicts the critical conditions (growth rate and wavenumber) at the onset of axisymmetric instability. In our experimental study, viscoelastic polyisobutylene (PIB)-based Boger fluids are electrospun. The axisymmetric instabilities observed are captured using high-speed photography, and the experimental instability growth rate and wavenumber are extracted from the digitized images. These are then compared with the stability analysis predictions. Both stability analysis and experiments show that increasing the fluid viscoelasticity up until a certain point results in a drastic stabilization of the axisymmetric mode. Such drastic stabilization of the axisymmetric mode by viscoelasticity coincides with the coil-stretch transition of polymer molecules in the unperturbed state. The examination of the disturbance-energy equation shows that both electric stress and polymeric stress give rise to strong stabilization. (c) 2007 Elsevier B.V. All rights reserved.