Keywords: electrospinning, nanofibers, nanocomposites, nanotechnology, evaporation, viscoelastic jet, electrohydrodynamics.

Nanofiber-reinforced composite materials are expected to demonstrate unique properties. Electrospinning is the most versatile and high-productive continuous nanofiber manufacturing method. Electrospinning is a process of elongation and drying of thin polymer jets in a high electric field with subsequent deposition of dried jets on a substrate as ultrafine continuous fibers with diameters ranging from several nanometers to several microns. Electrospinning is a cost-effective method that allows the production of hollow and multi-layered nanofibers, polymer, ceramic and metal fibers and fiber structures with random or oriented fiber distribution.

In this study, a discrete three-dimensional model of an unstable electrospun jet incorporating random jet instabilities and solvent evaporation was presented. Randomly oriented perturbations with random amplitudes are applied to each new jet segment instead of periodical circular undulations with constant amplitude in [1]. A Maxwell model was used to describe uniaxial elongation of polymer jet segments. Fick's law is employed to simulate the transient drying process. The mutual diffusion coefficient of the polymer/solvent system was calculated according Vrentas/Duda free volume theory [2] depending on the solvent mass concentration.

The system of equations was solved numerically by a coupled Verlet-based algorithm for bead three-dimensional motion and a Lagrangian finite difference scheme for the jet segment evaporation calculations. A numerical example of the PAN/DMF solution jet is considered. A parametric study for the evaluation of the influence of the evaporation rate on the unstable jet motion was performed. Jet shapes and fiber deposition for different values of the mass transfer coefficient were examined. Stress distribution and concentration profiles over jet cross-sections were obtained. Significant inhomogeneity in stress and concentration distribution for evaporating jets was observed and discussed.

Results in this study provide a better understanding of the electrospinning process and can be used for process control and optimization and for the analysis of more complex coupled chemophysical phenomena during the nanofiber formation in the electrospinning process.

1

D.H. Reneker, A.L. Yarin, H. Fong, S. Koombhongse, "Bending instability of electrically charged liquid jets of polymer solutions in electrospinning", Journal of Applied Physics, 87(9), 4531-4547, 2000. doi:10.1063/1.373532

2

J.M. Zielinski, J.L. Duda, "Predicting polymer/solvent diffusion coefficients using free-volume theory", AIChE Journal, 38, 405, 1992. doi:10.1002/aic.690380309

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