**2.5. Solvent properties**

Solvent properties including the surface tension [36] and conductivity [37], determine the final solution properties, and effect fiber properties indirectly. Solvent with low surface tension is a good candidate for better electrospinning solution preparation, thus the electrospinning process can be easily carried out by loading a relatively low voltage [36]. Volatility should be another concern when choosing the right solvent. If the volatility is too high, a blockage at the spinneret may occur from time to time [38]; if the solvent evaporates as slowly as water, then an adhesive and thick fiber may be obtained [39]. In addition, inadequate evaporation of the solvent in the spinning solution may cause a toxic solvent residual in fabrics, which is not wanted in medicinal and sensor applications [40]. Solution conductivity in electrospinning has been discussed. In a solution system, the selected solvent's conductivity is the first factor defining solution conductivity, and using additives to improve conductivity is the second factor considered to adjust the solution's conductivity [37].

**Figure 4.** SEM pictures of solution electrospun fibers at different temperatures and relative humidities [45].
