# Influence of Solvent Selection in the Electrospraying Process of Polycaprolactone
## 3 Selection of Solvent Systems Used in PCL Electrospraying
### Solution Properties for Cone-Jet in PCL Electrospraying
#### 3.2.1 Electrical Conductivity
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline
**PCL Molecular** & **Solvent** & **Concentration** & **Applied** & **Flow Rate** & \begin{tabular}{c} **Working** \\ **Distance** \\ \end{tabular} & \begin{tabular}{c} **Electrical** \\ **Conductivity** \\ **(cm)** \\ \end{tabular} & \
\begin{tabular}{c} **Surface** \\ **Tension** \\ **(fs/cm)** \\ \end{tabular} &
\begin{tabular}{c} **Viscosity** \\ **(fm/s)** \\ \end{tabular} & **Size (nm) and Morphology** & **Reference** \\ \hline
45,000 & toluene & 5 & 11-18.5 & 29-80 & 5 & - & 26.5 & 3.0 & 29-440, spherical and smooth & [126] \\
45,000 & toluene & 7 & 108-18.5 & 29-80 & 5 & - & 26.0 & 6.7 & 30-300, spherical and smooth & [126] \\
45,000 & toluene & 10 & 12-18 & 29-80 & 5 & - & 28.5 & 11 & 40-800, spherical and smooth & [126] \\
10,000 & toluene & 15 & 10-15 & 29-80 & 5 & - & 28.4 & 6.0 & 100-800, spherical and smooth & [126] \\
10,000 & toluene & 20 & 27-12.8 & 29-80 & 5 & - & 28.6 & 16 & 200-800, spherical and smooth & [126] \\
10,000 & toluene & 25 & 8.5-12.8 & 29-80 & 5 & - & 28.4 & 29 & 2.6 & 0-340, spherical and smooth & [127] \\
14,000 & dimethyl/tocamide & 2 & 7-10.5 & 25-80 & 2 & 3.4 & 29 & 2.6 & 0-340, spherical and smooth & [127] \\
14,000 & dimethyl/tocamide & 5 & 9-01.45 & 25-80 & 2 & 1.8 & 29 & 4.6 & 0-53, spherical and smooth & [127] \\
14,000 & dimethyl/tocamide & 10 & 9-15.5 & 25-80 & 2 & 0.8 & 32 & 11.1 & 30-52, spherical and smooth & [127] \\
4,000 & dimethyl/tocamide & 10 & 9-15.5 & 25-80 & 2 & 0.8 & 32 & 11.1 & 30-52, spherical and smooth & [128] \\
4,000 & dimethyl/tocamide & 3 & 12 & 16.67 & 12 & 0.02 & - & 24 & 128] \\
45,000 & dikhobenzene & 3 & 9-12 & 25 & 10 & 1.0 & 24.7 & 6.3 & 0-51, spherical and smooth & [129] \\
45,000 & dikhobenzene & 8 & 11-14 & 50 & 10 & 1.0 & 27.5 & 12.3 & -01,026, between and wrinkles & [129] \\
45,000 & dikhobenzene & 6 & 69-7.9 & 50 & 5-30 & 1.0 & 24.7 & 6.3 & 0-22-302, spherical and smooth & [130] \\
4,000 & dikhobenzene & 15 & 8 & 16.67 & 12 & - & - & - & 1291,000 & [129] \\
50,000 & dikhobenzene & 9 & 10 & 8.30 & 25 & - & - & - & 127.80 \(\pm\) 476, spherical and wrinkles & [92] \\
45,000 & dikhobenzene & 9 & 7.5 & 5 & 10 & - & - & - & 30-50, spherical and smooth & [92] \\ \hline \end{tabular}
\end{table} 
Table 3: Some solution properties for achieving cone jet during the PCL electrohydrodynamic process. In the use of a coaxial electrospray, the formation of cone-jet at the tip of the nozzle is also closely related to the electrical conductivities of inner and outer liquid phases [72; 131]. On the one hand, for a higher electrical conductivity of the inner liquid than the outer one, the free charges are located at the interface. In this case, inner liquids regard as the driving component and dominate the formation of the Taylor cone. Then, inner droplets are stretched into the conical shape due to the electrostatic forces acting on their surface, which leads to the transfer of the free charges to the surface of the outer phase. Finally, the formation of the Taylor cone of the outer liquid is done when the electrostatic attractions acting on the surface of outer liquid counteract the viscoelastic forces and surface tension (Figure 3a). On the other hand, a higher the electrical conductivity of the outer phase leads to the distribution of the free charges on its surface. The outer liquid dominates the formation of cone-jet of this configuration. In the first step, it is stretched into the Taylor cone due to the electrical attractions acting on its surface. The Taylor cone formation is only reached when the viscosity of the outer liquid is higher than the inner phase one (Figure 3b). According to [PERSON] and [PERSON] et al. [38; 84], the cone-jet during coaxial electrospray is easier to form in the case of inner driving, where the electrical conductivity of the outer liquid is less than that of the inner liquid. This principle is also applied to three-needle or four-needle coaxial electrospraying.