# Influence of Solvent Selection in the Electrospraying Process of Polycaprolactone
## 4 The Effect of Operating Parameters and Solution Properties in PCL Electrospraying
The flow rate of the electrospray solution as it passes through the nozzle is also an essential factor in the formation of the Taylor cone. The optimization of the setting of this parameter depends on the intrinsic characteristics of the prepared solutions, i.e., (i) saturated vapor pressure of the solvent, (ii) and the electrical conductivity of the solutions. In most cases, there are usually a lower and an upper flow rate limits allowing a stable jet formation. A Taylor cone is preferred for low flow rates since the uncharged liquid at the tip of the nozzle requires sufficient time to be polarized, and then polarized charges are generated on the droplet surface to promote Taylor cone formation. For higher flows, the reduction of the polarization time induces a continuous dripping of droplets due to gravity. Thus, in the case of PCL, depending on the choice of solvent, the flow rate values vary from several \(\upmu\)L/min to 50 \(\upmu\)L/min to obtain a stable conical jet. The use of a solvent with a high saturation vapor pressure requires a higher setting than other solvents to avoid clogging the nozzle when the solvent evaporates. On the other hand, a lower flow rate must be used for solutions prepared from solvents with a low saturated vapor pressure to ensure complete evaporation of the solvent during the solidification process. The conductivity value of the solutions influences the droplet polarization time, and therefore the adjustment of an adequate flow rate. Indeed, the polarization time of the droplets is longer to obtain when using solutions with low conductivity, which requires working at low flow rates. The adjustment range is widened, and the values increase for solutions with higher conductivity. On the other hand, in this case, an excessively high flow rate causes an accumulation of charges to accumulate at the end of the nozzle, and the stable conical jet breaks and turns into a multiple jet mode due to the too strong Coulomb repulsions of the charged droplets. In the case of coaxial electrodeposition, the flow rates of the internal and external liquids also affect the formation of the Taylor cone. In general, the Taylor cone is more easily obtained if the flow rate of the external liquid is higher than that of the internal [86]. For example, [PERSON] et al. concluded that the PS/PCL microcapsules with an incomplete core-shell structure as well as irregular morphology were obtained when the flow rate of outer liquid was the same than the inner one. The increase of the flow rate ratio (outer /inner liquids) from 1:1 to 4:1 allowed to prepared complete core-shell structure with a smooth morphology [159]. Otherwise, the conical jet is challenging to form, and an incomplete encapsulation of the system with an irregular morphology is obtained. [PERSON] et al. also found that the working range of the voltage applied to the stable cone-jet mode can be extended by increasing the flow rate of the internal liquid and decreasing that of the external by considering it as a driving fluid [131]. The working distance, between the top of the tip and the collector, is adjusted to adapt the intensity of the electric field in order to ensure the formation of the Taylor cone, i.e., at a constant voltage, shorter