Solution viscosity, solution conductivity, applied voltage, distance from tip to collector, atmospheric pressure, surrounding humidity, and volumetric flow rate, all affect the electrospinning process and resulting fibers. Investigation of the effect of these parameters can lead to a comprehensive understanding of electrospinning, that helps us to manipulate the morphology of the resulting fibers.
Two main topics were investigated in this work. One is the effect of the solution conductivity. The other is the influence of the applied voltage. Potential applications of the collected fibers are considered.
By increasing the salt (lithium chloride) concentration of the solution, the conductivity of the solution becomes higher. The resulting electrospun products varied from separate particles to beaded fibers to smooth fibers, with the increase of the concentration of ions from the dissolved salt. A new, reproducible phenomenon associated with the bending instability was observed by adding salt and adjusting the applied voltage. The highly conducting jet formed a bending instability coil with a slender envelope cone first. These slender coils were subsequently incorporated into a larger diameter bending instability coil with a more rapidly growing diameter. This complicated process contributed to the formation of garlands of interconnected loops. Entangled branching and splitting fibers were sometimes observed. When present, these branching and splitting fibers also contributed to the garland formation. The splitting fibers are associated with excess ions on the jet, which increases the electrical conductivity and reduces the time required for the electrical potential on the sample to equilibrate.
When a higher concentration polystyrene solution was electrospun, by adjusting the applied voltage, bending coils, developed on the straight segment, grew larger in diameter for a short distance and then grew smaller, re-forming the straight segment. The bending instability was turned on and off. By setting the appropriate applied voltage, the bending instability was controlled. Uniform and long polystyrene loops were created by a buckling process on a moving collector. These patterns of small loops can be placed precisely by a programmed machine or by hand. It works like a tiny sewing machine that creates coils instead of stitches. Fluffy bundles of coiled fibers can be produced, which may, for example, find applications for deliberate formation of blood clots to prevent bleeding or to stop the blood supply to a tumor.