# Optimizing the Shape of the Spinning Electrode for Needleless Coaxial Electrospinning
## 3 Experiments
### Methods  
Laboratory experiments were conducted to verify the optimized design and analysis of the electric field near the spinning electrodes. The experiments were performed at an ambient temperature of 21-23 \({}^{\circ}\)C and a relative humidity of 37-38%. The optimized spinning electrode, tipped with plastic spheres, as shown in Figure 11a, was operated in an air-conditioned spinning chamber. The electrode (wire position) was clamped in the spinner's stand and placed 110 mm below the spinner collector. After forming a uniform double layer of the polymer solution, a high voltage (HV) was applied to the electrode. The initial HV value was set at +10, \(-\)8 kV and was gradually increased. The following value of the applied voltage was recorded: the critical voltage value (the voltage at which the spinning process started). The optimal spinning value and the maximum voltage value were reached; at this point, the spinning process was still smooth and uninterrupted by discharges. Testing began at a +12, \(-\)10 kV supply voltage. The voltage was increased up to a value of +25, \(-\)20 kV when corona discharges were observed on the plastic spheres, and after a further increase, the first Taylor cones were visible. Optimal spinning was found at an HV of +33, \(-\)30 kV. However, the process was accompanied by the creeping discharge observed on plastic spheres. This discharge did not significantly affect the spinning process.  
Spinning was recorded using the CoroCAM. Via this equipment, it was possible to monitor the development of the spinning process and the influence of attached spheres. The image from the camera capturing continuous surface spinning is shown in Figure 11b. The image shows many polymer nozzles without corona discharges, which would hurt the spinning process.  
Experiments have shown that spheres with optimized diameters positively affect the course of the spinning process. The uniform distribution of the electric field intensity results in uniform electrospinning from the entire surface of the polymer solution. The spinning process was negligibly affected by creeping discharges that arose at the transition  
Figure 10: Electric field distribution for optimized electrode with metal spheres.  
point between the metal part of the electrode and the plastic spheres. The spinning process was not negatively affected by corona discharges caused by a place with a high-intensity electric field (at sharp edges) at the electrode, as was the case with the previous variant of the electrode.  
The functionality of the optimized electrode with metal spheres, as shown in Figure 12a, was also verified experimentally. The experiment was carried out in the same way and under the same conditions as in the previous case. Figure 12b shows a recording made using a CoroCAM. The same behavior can be observed here as in the case of the electrode with plastic spheres. Using metal spheres placed at the ends of the electrode significantly contributed to eliminating corona discharges. The use of metal spheres further contributed to the uniform distribution of the electric field and, thus, to the more uniform formation of Taylor cones.