# Optimizing the Shape of the Spinning Electrode for Needleless Coaxial Electrospinning
## 1 Introduction
During the passage of the bending instability nozzle, most of the solvent evaporates, and the finished dried nanofibers are deposited on the collector with the opposite charge to the electrode, as shown in Figure 1.  
The advantage of needleless spinning is primarily an increase in the productivity of nanofiber production. Another advantage is a more even distribution of the electric field around the spiner, compared to the inhomogeneous electric field in the case of a system of needles. The article deals with optimizing the shape of a new spinning electrode designed  
Figure 1: Schematic representation of needleless electrospinning. for coaxial electrospinning technology [25]. Coaxial fibers are mainly produced by spinners equipped with needle coaxial electrodes. In general, the disadvantage of needle electrodes is low productivity and the small width of the produced layer of nanofibers. Therefore, the effort is to develop an electrode for ensuring the high productivity of nanofibers from the free surface. Some types of these electrodes are known from previous research, such as the cylinder coaxial or weir coaxial electrodes [26]. In this article, the focus is on optimizing the weir coaxial electrode. Figure 2a shows the new design of a coaxial electrode that allows production from the free surface of the polymer solution with its 80 mm width, while the total length of the electrode is 120 mm. Figure 2b shows a schematic cross-section of the electrode to clarify its functional principle. The spinning electrode consists of two chambers, one for the supply of internal spun material and the other for the supply of external spun material. The chambers feed the spinning material and are divided by a plastic partition. A metal wire with a 1 mm diameter is placed at the outlet of the electrode chambers, to which high electric voltage is applied. Both polymer solutions flood the wire and create two separate layers, with the upper solution forming fibers and the lower solution being drawn into the fibers, forming a core in the resulting coaxial nanofiber. The non-fibrous solution is drained into a collection container, as shown in Figure 2a and reused in the spinning process. The main disadvantage of this electrode is the high probability of spark discharges in places with a high concentration of electric field intensity. The occurrence of roe discharges adversely affects the spinning process, and, therefore, efforts were made to suppress this phenomenon. An example of the occurrence of spark discharges is shown in Figure 3. From that figure, spark discharges at both ends of the overflow spinner can be observed, which cause the leakage of electrical energy and a reduction in spinning productivity. The development of the electrode further dealt with the design of shape changes to suppress unwanted corona discharges. Eliminating corona discharges is very important, especially from the following points of view, which contribute to the stability of the production process. The most important thing is safety, as polymer solutions based on alcohol and other explosive solvents can ignite and explode. Another point of view is the parasitic consumption of electric power by corona discharges. Therefore, it is essential to minimize energy losses arising due to the non-optimal shape of the electrode. Figure 2: (**a**) The original design of the coaxial spinner; (**b**) Scheme of weir coaxial electrode principal.