Axisymmetric instabilities in electrospinning of highly conducting, viscoelastic polymer solutions

In this paper the axisymmetric instabilities observed during the electrospinning of highly electrically conducting, viscoelastic poly(ethylene oxide) (PEO)/water solutions are investigated. In our theoretical study, a linear stability analysis is coupled with a model for the stable electrospun jet. The combined model is used to calculate the expected bead growth rate and wave number for given electrospinning conditions. In the experimental section of the study, PEO/water solutions are electrospun and the formation of axisymmetric beads is captured using high-speed photography. Experimental values for the bead growth rate and wave number are extracted and compared with the model predictions. An energy analysis is then carried out on the stability results to investigate the mechanism of instability via the coupling between base flow and perturbation. The analysis reveals that the unstable axisymmetric mode for electrically driven, highly conducting jets is not a capillary mode, but is mainly driven by electrical forces due to the interaction of charges on the jet. We note that this axisymmetric, conducting mode often exhibits a growth rate too small to be observed during electrospinning. However, both our experiments and stability analysis demonstrate that the axisymmetric instability with a high growth rate can be seen in practice when the electrical force is effectively coupled with viscoelastic forces. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3246024]