the wagner group















Electrospinning

Electrospinning is a process by which continuous polymer fibers of sub-micron diameter (like those shown at right) can be drawn using an electric field. When a strong electric field is applied to a capillary containing a polymer solution or melt, the resulting force is enough to overcome surface forces in the capillary, causing elongation of the liquid/air interface into a free liquid jet that is propelled toward a collection plate. Unlike low viscosity fluid jets, where minute pressure gradients causes disturbance and eventual breakup of the jet, polymeric jets retain stability due to viscoelastic forces that hold the jet together. As the jet travels, elongation of the jet combined with solvent evaporation causes the formation of solid nanofibers.

Previously developed applications of electrospun polymer nanofibers are in filtration, as well as high strength and lightweight materials. However, electrospun nanofibers are well-suited for a variety of emerging applications in the area of nanotechnology due to their small dimensions and large surface area. Such applications include biomaterials for tissue engineering and drug delivery, pre-cursors for catalyst production and nanotemplating, as well as a variety of chemically and electronically active composites.

Despite the widespread and rapidly growing use of electrospinning as a synthesis technique for novel nanomaterials, the process itself is poorly understood, and there are no simple methods of predicting a priori the properties of electrospun fibers from knowledge of the spinning solution properties and electrospinning operating conditions alone.

The goals of this project are to develop an engineering understanding of electrospinning from the fundamental physics of the process. We have used simple semi-empirical analysis to correlate important fluid properties and operating parameters to electrospun jet and eventual fiber morphology, allowing for a deeper understanding of dominant physical phenomena. We have also used complimentary experimental techniques to examine the complicated fluid mechanics of electrospun jets, allowing for direct correlation of electrostatic stresses to the non-Newtonian behavior of polymer solutions. Overall, we hope to use such tools as a means to fuse theory and experiment and allow for the a priori design of novel materials by the electrospinning process.

Publications

M.E. Helgeson, K.N. Grammatikos, J.M. Deitzel, and N.J. Wagner. "Theory and kinematic measurements of the mechanics of stable electrospun polymer jets", Polymer 2008 49(12): 2924-2936.   [doi]

M.E. Helgeson and N.J. Wagner. "A correlation for the diameter of electrospun polymer nanofibers", AIChE Journal 2007 53(1): 51-55.  [doi]

V.K. Daga, M.E. Helgeson, and N.J. Wagner. "Electrospinning of neat and laponite-filled aqueous poly(ethylene oxide) solutions ", Journal of Polymer Science B: Polymer Physics 2006 44(11): 1608-1617.  [doi]

V.K. Daga and N.J. Wagner. "Linear viscoelastic master curves of neat and laponite-filled poly(ethylene oxide)-water solutions", Rheologica Acta 2006 45(6): 813-824.  [doi]