ABSTRACT
114A charged polymer jet uses accelerate and stretch by an external electric field for producing ultrafine nanofibers. Electrohydrodynamic models for electrospinning Newtonian jets are proposed in this chapter. A problem arises, however, with the boundary condition at the nozzle. Unless the initial surface charge density is very small near zero, the jet bulges out upon exiting the nozzle in a ballooning instability, which never occurs in reality. The stretching of an electrified jet is governed by the interplay among electrostatics, fluid mechanics and rheology, and the role of viscoelasticity. This chapter presents a slender-body theory for the stretching of a straight charged jet of Giesekus fluid. Results show strain-hardening as the most influential rheological property. It causes the tensile force to rise at the start, which enhances stretching of the jet. Further downstream, however, the higher elongational viscosity tends to suppress jet stretching. In the end, strainhardening leads to thicker fibers. This confirms the main result of a previous study using empirical rheological models. The behavior of the electrically driven jet forms an interesting contrast to that in conventional fiber spinning.
