Phases in Electrospinning Jet

Upon initiation of electrospinning, most jet shows a two distinctive phase, the stable phase and the bending instability phase. The stable phase usually has a length of about 10 mm or less and its length is influenced by several parameters (Read more). Thereafter, bending instability sets in and the fiber is spread over a deposition area of about 10 cm or more at the point of collection. The video below shows the stable phase to the left and the bending instability on the right.

Viewed using a high speed video, the bending instability typically shows a fluctuating spiraling jet path (See video below). It is thought that this spiraling jet path significantly increases the distance traveled by the jet thereby allowing the fiber to be stretched down to the nano-meter dimension.

To have a visual impression of the microstructural transformation of the electrospinning jet, Bafekrpour et al [2012] used a coagulation bath to collect the fiber at distance of 2 cm to 10 cm from the electrospinning tip while maintaining the same electric field intensity as the normal setup (flat plate collector) at each distance interval and observed the fiber structure under the scanning electron microscope (SEM). The study showed beaded fibers at distance closest to the tip and the beads gradually elongates as the coagulation bath gets further from the spinning tip. This result provided evidence that the solvent rich solution at the preliminary stage of the spinning process contains numerous beads at close proximity to one another. In the model described by Hohman et al (2001), a perfect dielectric solution will have its velocity perturbation is out of phase with the radius perturbation and this will show up as bulging regions on the fluid during the growing mode. The results from Bafekrpour et al (2012) is in agreement with the observation and the model described by Hohman et al (2001) where their strobe photograph showed blob-like varicose protrusions along the unstable electrospinning jet. As the fiber stretches and the solvent evaporates, the beads are stretched until a smooth fiber is formed given sufficient stretching distance.

Figure 1. Schematic showing the microstructural changes in the spinning fiber over the distance travelled between the tip and the collector.