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The International Istanbul Textile Congress 2013 May 30th to June 1th 2013, Istanbul, Turkey

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HV PROBE ANGLE EFFECT ON JET BENDING INSTABILITY DIRECTION IN ELECTROSPINNING SYSTEMS

F. MEMARIAN1, F. ZEIGHAMI1, M. AMANI TEHRAN1, M. LATIFI2

1Textile Engineerin Department, Amirkabir University of Technology, Tehran, Iran 2Textile Excellence & Research Centers, AmirKabir University of Technology, Tehran, Iran

[email protected] Abstract: Despite recent advances in electrospinning, there are still many unknown parameters affecting this process. In the present study we illustrated that the deposition location of the nanofibers can be varied by varying the way that high voltage probe is connected to the needle. We have indicated that precise positioning of nanofibers is depended upon the angle between the probe and the needle. Probe direction also has main effect in shifting the polymer jet’s bending instability and therefore the nanofibers’ deposition location. The effect of these parameters has a critical role in yarn production processes and other applications in which jet direction and fiber position is vital. Therefore the scope and reasons of this phenomenon has been discussed tenuously. Keywords: Electrospinning, bending Instability, deposition location, nanofibers. 1. Introduction

Electrospinning is a cost effective and straightforward method of producing submicron scale nanofibers which has attracted increasing attention of the researchers in the last decades [1].

Also electrospinning set up is very simple but the process is very complicated. When a sufficient high electrified field is applied, the electrostatic forces overcome the surface tension of the polymer solution and cause the ejection of a thin jet from capillary nozzle which undergoes stretching and whipping process [2].There are lots of studies on taylor cone, the jet initiation and bending instabilities [3-5]. However no one has noticed the effect of the HV probe angle which can affect the direction of jet bending instability. It seems as if this issue is not very effective in the electrospinning process. However when precise deposition on some points of the collector is desirable, as in yarn production processes, then the effect of HV probe angle is significant. Therefore we have studied this subject in this study.

2. Materials and Methods Nylon 66 was purchased from Sigma-Aldrich (Molar Mass: 30500). Pure formic acid (merck chemical) was used as the nylon solvent and 10wt/wt% solution was prepared and magnetically stirred for 12hr in room temperature.

In the electrospinning process a syringe pump (KDS100 and KDS200, Cole-Parmer, USA) and a high-voltage power supply (ZGF60 kV/2 mA, Shanghai Sute Corp., China) were used. The applied voltage was fixed at 12 kV through some pre-experiments. The syringe and its needle were placed horizontally. The high voltage emitting probe of positive polarity was attached to the needle. The nanofibers produced were collected on aluminum foil at a distance of 10 cm. The electrospinning process was carried out in a glass box and the high voltage prob was placed outside and inside the box. Also the probe position to the needle was changed. In all these situations electrospun samples were produced, keeping all the other factors unchanged. 3. Results As the first step, the high voltage probe was placed perpendicular to the needle in 4 different angles as is shown in figure 1. In each position an electrospun sample was collected after 10min.


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Figure 1. The high voltage probe position according to the needle

The images of the samples are shown in figure 2. As it is clear, although all the electrospinning factors remained unchanged but nanofibers deposited in different locations on the collector, absolutely depending on the probe position. In all the samples, nanofibers deposit in the opposite direction to the probe angle trying to be placed in the farthest position to the probe on the collector.

Figure 2. The images of the samples after 10min electrospinning by placing the probe in: a) 0 degree position, b) 90

degree position, c) 180 degree position, d) 270 degree position.

As it is known in the common electrospinning process, a strong electric field is used to draw a solution from the tip of a capillary to the collector. The electrostatic field causes a pendant droplet of the solution at the capillary tip to deform into a conical shape or a Taylor cone. When the electrical force at the surface of the solution overcomes the surface tension a fine, charged jet is ejected [6]. The fiber stretching in electrospinning is a fast and incessant process, which can be divided into three consecutive stages: jet initiation, whipping instability, and fiber deposition. From the initial jet to dry fibers, the fiber stretching process takes place in milliseconds [7].

In this process the high voltage probe plays a dual role: it charges the needle and the polymer solution and besides it exerts a force on the polymer jet since the probe is charged. The force exerted by the probe is a repellent force as it is the force between the two same charged objects. As the result of this force the bending instability and therefore the nanofibers’ deposition location changes and moves to the furthest possible place.

To verify our hypothesis we conducted the second step experiments. If the probe had no effect we expected the nanofiber web to deposit on a circle which its center is the meeting point of the elongated line from the needle by the collector surface, supposing that the syringe and needle axis is prependicular to the collector


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surface. Therefore if we eliminate the probe force, the samples should deposit on the same location independent of the probe angle. So the high voltage probe was placed out of the box and in 0 and 180 degree positions as it is indicated in figure 3. Same as step one, in each position an electrospun sample was collected after 10min.

Figure 3. The high voltage probe and the glass wall position according to the needle

The images of the samples are shown in figure 4. As it can be seen in figure 4 by changing the probe angle the nanofiber deposition location did not change. This means there is no extra force exerted from the probe affecting the bending instability and therefore the nanofibers’ deposition location.

Figure 4. The images of the samples after 10min electrospinning by placing the probe outside the box in: a) 0degree position, b) 180 degree position.

Another point that can be helpful is that the unwanted effects of electrospinning setup parts, such as wires, probes, and indicators, can be eliminated by surrounding the main part using a thick enough dielectric wall such as a glass wall. This would increase the accuracy of the electrospinning process and helps to remove the unwanted and unknown factors. 4. Conclusion

Effect of probe on the deposition position of nanofibers in an electrospinning process was studied. It was found that probe angle has a repellent force on the jet which influences the deposition location of nanofibers. We suggest that probe must be located outside the electrospinning box for more precise electrospinning and to be able to predict the location of nanofibers on the collector.

References [1] Kilic, A.: Oruc, F.: Demir, A.: Effect of Polarity on Electrospinning Process, Textile Research Journal, 78.

(2008), 6., pp. 532-539. [2] Li, B D.: Wang, Y.: Xia, Y.: Electrospinning Nanofibers as Uniaxially Aligned Arrays and Layer-by-Layer

Stacked Films, Advanced Materials, 16. (2004),4., pp. 361-366. [3] Thompson, C J. etal: Effects of parameters on nanofiber diameter determined from electrospinning

model, Polymer, 48. (2007), pp. 6913-6922. [4] Theron, S.A.: Yarin, A.L.: Kroll, E.: Multiple jets in electrospinning: experiment and modelling, Polymer,

46. (2005), pp. 2889-2899. [5] Xie, S.: Zeng, Y.: Effects of Electric Field on Multi needle Electrospinning: Experiment and Simulation

Study, Industrail and Engineering Chemistry Research, 51. (2012), pp. 5336-5345.


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[6] Panels, J E.: Joo, Y L.: Incorporation of Vanadium Oxide in Silica Nanofiber Mats via Electrospinning and Sol-Gel Synthesis, Journal of Nanomaterials, (2006), pp. 1-10

[7] Jian, F.: Hongxia, W.: Haitao, N.: Tong, L.: Xungai, W. Evolution of Fiber Morphology During Electrospinning, Journal of Applied Polymer Science, 118. (2010), pp. 2553-2561.

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