Electrospinning and electrically forced jets. I. Stability theory

Electrospinning is a process in which solid fibers are produced from a poly meric fluid stream (solution or melt) delivered through a millimeter-scale nozzle. The solid fibers are notable for their very small diameters (<1 mum ). Recent experiments demonstrate that an essential mechanism of electrospi nning is a rapidly whipping fluid jet. This series of papers analyzes the m echanics of this whipping jet by studying the instability of an electricall y forced fluid jet with increasing field strength. An asymptotic approximat ion of the equations of electrohydrodynamics is developed so that quantitat ive comparisons with experiments can be carried out. The approximation gove rns both long wavelength axisymmetric distortions of the jet, as well as lo ng wavelength oscillations of the centerline of the jet. Three different in stabilities are identified: the classical (axisymmetric) Rayleigh instabili ty, and electric field induced axisymmetric and whipping instabilities. At increasing field strengths, the electrical instabilities are enhanced where as the Rayleigh instability is suppressed. Which instability dominates depe nds strongly on the surface charge density and radius of the jet. The physi cal mechanisms for the instability are discussed in the various possible li mits. (C) 2001 American Institute of Physics.