See Student projects

Developing and testing a program to (real-time) trace the fluid interface during electrospinning

Introduction

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 [1].

Assignment

A Scanning Electron Microscope (SEM) micrograph of an electrospun fiber mat is shown in Figure 2. In the image, the unaligned fibers of non-uniform thickness are clearly visible.

Figure 2: A SEM micrograph of an electrospun fiber mat. The fibers show a very non-uniform thickness and are not aligned.

In order to make electrospinning a more versatile fiber fabrication procedure, one would like to have full control of the deposition location of the fiber. The main reason of the random fiber deposition location is the vigorous whipping of the fiber just after it has been produced [3]. A photograph of a fiber during electrospinning is shown in Figure 3.

Figure 3: A photograph of a fiber during electrospinning. The fiber makes a whipping motion, as it does not traverse towards the substrate in a straight path. Figure adapted from [2]

In order to understand and investigate the (onset of the) fiber instability, the electrospinning setup is equipped with an optical microscope and (high-speed) camera which will be used to monitor the motion of the fibers. The gathered images need to be processed in a program so that information such as fiber thickness and whipping frequency can be extracted.

First, the student should get familiar with the experimental setup, especially with the optics and cameras used. Next, the student should develop a program which can be used to extract (real-time) images generated by the camera used. The program should also compute or determine the fiber thickness as a function of fiber traversal distance and whipping frequency (if the high-speed camera is used). Lastly, the student will perform electrospinning experiments with different electrospinning mixtures: It is expected that different electrospinning mixtures (from which, for example, the fluid viscosity is altered) yield different fiber thicknesses and instability modes. The student uses dimensional analysis to relate different experimental phenomena to the theory and provides recommendations to make the electrospinning process more stable.

We would like to stress that this project is only suitable for students who have an affinity with image analysis and statistics.

More information

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 (j.g.e.gardeniers@utwente.nl) or Bjorn Borgelink (b.t.h.borgelink@utwente.nl).

REFERENCES

[1] 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.

[2] D. H. Reneker et al. “Bending instability of electrically charged liquid jets of polymer solutions in electrospinning”. In: Journal of Applied physics (2000).

[3] A. L. Yarin, S. Koombhongse, and D. H. Reneker. “Bending instability in electrospinning of nanofibers”. In: Journal of Applied Physics (2001).