## 3 Results and Discussion  
### Properties of PVA/Zinc Citrate Mixtures  
Viscosity of electrospinning solution is an important index for electrospinning, and thus it is an important parameter for both conventional single-needle electrospinningning and needleless electrospinningning. When the viscosity of electrospinninging solution falls in an optimal range, it has a significant influence on the morphology of fibers [40]. The viscosity of PVA solution increases from489.9 mPa s to 992.3 mPa s as a result of an increase in zinc citrate, as indicated in Table 1. Zinc citrate is slightly water soluble, and thus its particles are dispersed in a PVA solution shown in Figure 3. Increasing the concentration of zinc citrate causes the reaction between zinc citrate and molecular chains, and thereby results in chain entanglements. As a result, viscosity of solution is proportional to the amount of zinc citrate. Table 1 indicates that the PVA/zinc citrate mixture that contains 5 wt % zinc citrate has a higher electrical conductivity of 1.28 \(\times\) 10\({}^{3}\) uS/m, compared to the control group (0.57 \(\times\) 10\({}^{3}\) uS/m). Zinc citrate is an ionic compound that has electric charges. The zinc ions are released after zinc citrate is slightly dissolved in water, as indicated in Figure 4, which effectively strengthens the electrical conductivity of the mixtures. As indicated in the study by [PERSON], the addition of metal compounds causes the electrical conductivity to increase [39]. Effects of Amount of Zinc Citrate on Morphology and Fiber Diameter of PVA/Zinc Citrate Nanofiber Mats  
The morphology and diameter distribution of PVA/Zinc citrate nanofiber mats are indicated in Figure 5. The pure PVA nanofibers have a smooth morphology, and there are no beads or spindle apparatus observed in Figure 5a. The PVA/zinc citrate nanofiber mats are formed differently with the corresponding amount of zinc citrate as follows: spindle (0.5 wt %), small beads (1 wt %), beads \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Physical Properties**} & \multicolumn{4}{c}{**Zinc Citrate Content (wt\%)**} \\ \cline{2-5}  & **0 wt \%** & **0.5 wt \%** & **1 wt \%** & **3 wt \%** & **5 wt \%** \\ \hline Viscosity (mPa s) & 489.9 & 708 & 920.4 & 942.4 & 992.3 \\ conductivity (uS/m) & 0.57 \(\times\) 10\({}^{3}\) & 0.62 \(\times\) 10\({}^{3}\) & 0.70 \(\times\) 10\({}^{3}\) & 0.98 \(\times\) 10\({}^{3}\) & 1.28 \(\times\) 10\({}^{3}\) \\ Average diameter (nm) & 95 \(\pm\) 22 & 79 \(\pm\) 26 & 72 \(\pm\) 18 & 75 \(\pm\) 24 & 84 \(\pm\) 22 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Viscosity of polyvinyl alcohol (PVA)/zinc citrate mixtures and specification of nanofiber mats. Figure 4: Dissociation mechanism that zinc citrate releases electric charges after it is dissolved in water. Figure 3: The dispersion of zinc citrate in PVA/zinc citrate mixtures that contain **(a)** 0.5 wt %; **(b)** 1 wt %; **(c)** 3 wt %; and **(d)** 5 wt % zinc citrate. The mixtures are kept at room temperature a fortnight. and droplets (3 wt %), and beads and flat fibers (5 wt %), as indicated in Figure 5b-e. Such results are ascribed to the viscosity of the polymer solution. The viscosity of the polymer solution is proportional to the amount of zinc citrate, as indicated in Table 1, and thus a high viscosity is disadvantageous for electrospinning. In addition, SEM images also indicate that a high amount of zinc citrate increases the viscosity of PVA/zinc citrate mixtures, which prevents the solvent to volatilize for the fiber formation. Thus, there are some ill-formed fibers observed in the SEM images. In addition, Figure 5b-e indicates that the nanofibers have a distinct beaded-structure when the mixtures contain a greater amount of zinc citrate. This result is because zinc citrate particles and PVA are electrospun into nanofibers, and the particles are then attached to the surface of PVA nanofibers.