(297e) Understanding Polymer Nanofiber Electrospinning: Kinematic Measurements and Dimensional Analysis

Polymer electrospinning has gained much attention for its ability to produce polymer and composite nanofibers from a solution or melt. However, electrospinning behavior arising from complex interactions between electrostatics, non-Newtonian rheology, and free surface flows is poorly understood. The present work outlines the results of recent efforts aimed at developing and experimentally verifying an engineering understanding of the electrospinning process. High speed videography was used for the direct measurement of the kinematics of electrospinning jets of aqueous poly(ethylene oxide) seeded with tracer particles under various operating conditions. The results of particle tracking velocimetry validate several important assumptions and conclusions typically found in analytical models for electrospinning. Specifically, the assumptions of negligible mass transfer and the slender body approximation are experimentally verified. Further, we find that the jet profile asymptotes to the scaling predicted by electrohydrodynamic theory. Additionally, the velocity profile in the developing jet follows that expected for steady uniaxial extensional flow near the jet origin, thus defining an effective rate of extension for electrospinning. The extension rate is correlated with process conditions and solution rheology, and trends in the jet morphology are argued in terms of strain hardening of the electrospinning fluid. Finally, using previously developed electrohydrodynamic models as a framework, a semi-empirical dimensional analysis of the electrospinning process is developed and applied to electrospinning data taken for several polymer-solvent systems presented in the literature. The results show universal behavior that correlates process parameters and fluid properties to ultimate fiber morphology.