## 3 Results and Discussion
It was observed that both were increased with the flow rate, and voltage resulted in microparticles with monodispersed properties and a minimum diameter. From these results, it can be concluded that the effects of voltage and flow rates played a promising role in particle size and morphology. Presumably, the reasons for the homogeneous distribution of polymer particles are that the applied voltage and flow rate affected the evaporation time and chain entanglement. It can be noted that SEM experiments were performed for those samples, which exhibited spherical and uniform shapes that were observed under the optical microscopy experiments. Further, the effects of flow rate and voltage on particle morphology were not studied separately in this work. As mentioned, evaporation of the solvent has a crucial role in the electrospray technique to obtain monodispersed and uniform-sized particles. Dichloromethane (DCM) is a volatile solvent and was used for obtaining PLA microparticles. While electrospray, after droplet formation occurred, the DCM was evaporated slowly until the droplet reached a glass slide and porous particles were obtained. Some microfiber structures were also obtained as the concentration of the polymer was increased to 4 wt.% of PLA (which was checked with the optic microscope; an optical microscopy image is not shown). For the 4 wt.% PLA-DCM group, the flow of the biopolymer solution was unstable, and the Taylor cone was not formed. Additionally, microfiber formed on the nozzle tip, which is not a suitable condition for the production of microparticles. When polymer concentration decreased to 1 wt.% PLA, turbulence flow occurred and resulted in the less uniform and regular distribution of the particles. The concentration of PLA was fixed at 3 wt.% according to the above optimization and previous research [12; 23; 24; 29]. The relationship between flow rate and voltage was investigated to find the best PLA microparticles. [PERSON] et al. prepared PLA samples in different solvents and could not obtain uniform and monodisperse microparticles in the 5% PLA-DCM sample [30]. However, in this study, when SEM images of the 3 wt.% PLA-DCM sample were analyzed, a homogeneous, spherical and porous microparticle was obtained as shown in Figure 4A, at 18 kV, with a flow rate of 20 \(\upmu\)L/min. However, at 18 kV, the flow rate of 15 \(\upmu\)L/min and the non-spherical microparticle were formed (see Figure 4B). These results obtained might be because the flow rate was not critical enough to obtain the spherical droplets. This can be interpreted as the flow rate of the PLA-DCM solution being slow. Therefore, the applied electrical field was not enough to obtain microspheres [29; 31; 32]. Since a 20 \(\upmu\)L/min flow rate gives more suitable particles, it was decided to investigate the effects of voltage on the 20 \(\upmu\)L/min flow rate. In this work, three voltages (14 kV, 16 kV and 18 kV) were applied to the PLA-DCM solution in order to show the effects of applied voltage on the morphological features of the microparticles generated. From the obtained results, it is seen that 18 kV was the most appropriate voltage setting for the production of particles with the best morphology as is seen in Figure 4A. The morphology of the microparticles was disrupted at 14 kV and 16 kV. Furthermore, the intensity of microparticles was smaller in number for 14 kV and 16 kV as seen in Figure 4A. Figure 3: SEM images and particle size distribution profile of 3 wt.% PLA ethanol–chloroform group. (**A**) The effect of voltage to particle shape in a constant 12 \(\upmu\)L/min flow rate. Each line contains both SEM images and a size distribution profile of 26, 27 and 28 kVA, respectively. (**B**) SEM images and size distribution profile of 15 \(\upmu\)L/min flow rate 30 kVA particles. The possible explanation for this is that the low voltage might not be enough for the surface tension of the solution [29; 31; 32]. When the voltage was decreased, the electrical field might be less to obtain spherical droplets.