To fabricate and deposit micro and nanosized (polymer) fibers, a method called electrospinning is used. A typical electrospinning setup is depicted in Figure 1.
Figure 1: A schematic drawing of an electrospinning setup. The blue part in the syringe shows the electrospinning mixture
An electrospinning setup typically comprises of a capillary which is fluidically connected to an electrospinning mixture feed mechanism and is electrically connected to a high voltage (HV) power supply. The power supply changes the electrical potential of the capillary with respect to the grounded substrate, which is located approximately 10 cm below the capillary. The electrospinning mixture is pumped through the capillary (for example by means of a syringe pump) and forms a droplet at the end of the capillary. If the local electric field near the end of the capillary is strong enough, a thin fiber emanates from this droplet and moves towards the substrate .
As depicted schematically in Figure 1, the electrospun fiber is first traversing in a straight path towards the substrate. However, the length in which the fiber remains stable (i.e. it traverses in a straight path) is limited. There exist only a few models that give possible explanations for why the instability occurs [2, 3, 5, 7, 8].
The electrospinning mixture typically comprises of a solid material (e.g. a polymer or a perovskite) and a solvent (e.g. water or ethanol). We believe that the location at which the fiber becomes unstable is related to the rapid decreasing solvent concentration in the fiber. Important physical parameters such as the mixture’s viscosity, surface tension, electrical conductivity, and dielectric constant are known to change as a function of solvent concentration [1, 6]. In order to validate or enhance the contemporary models, the change of all important physical parameters of the solvent concentration needs to be measured and analyzed.
The student should start with a literature review on the existing models which describe the (onset of) the instability of the electrospun fiber. In order to efficiently and reliably measure the change of the mixture’s physical parameters, the student should set up a measuring plan or perform a design of experiments. Next, the student determines how the physical parameters of the electrospinning mixture alter as a function of the solvent concentration. Lastly, the gathered data is analyzed and reported by the student.
Are you interested in this attractive project or do you have any questions about the project? Do not hesitate to contact either Prof. Dr. Han Gardeniers (firstname.lastname@example.org) or Bjorn Borgelink (email@example.com).
 Theodore L. Bergman et al. Incropera’s Principles of Heat and Mass Transfer. John Wiley & Sons Inc, 2017.
 M. Cloupeau and B. Prunet-Foch. “Electrohydrodynamic spraying functioning modes: a critical review”. In: Journal of Aerosol Science (1994).
 D. Deshawar and P. Chokshi. “Stability analysis of an electrospinning jet of polymeric fluids”. In: Polymer (2017).
 J. J. Feng. “The stretching of an electrified non-Newtonian jet: A model for electrospinning”. In: Physics of fluids 14.11 (2002), pp. 3912–3926.
 M. M. Hohman et al. “Electrospinning and electrically forced jets. I. Stability theory”. In: Physics of Fluids (2001).
 L. D. Landau and E. M. Lifshitz. Fluid Mechanics. Elsevier Science & Technology, 1987.
 D. H. Reneker et al. “Bending instability of electrically charged liquid jets of polymer solutions in electrospinning”. In: Journal of Applied physics (2000).
 A. L. Yarin, S. Koombhongse, and D. H. Reneker. “Bending instability in electrospinning of nanofibers”. In: Journal of Applied Physics (2001).