# Influence of Solvent Selection in the Electrospraying Process of Polycaprolactone
## 3 Selection of Solvent Systems Used in PCL Electrospraying
### Hansen Solubility Parameter
The amount of entanglement influences the morphology and size of the resulted product during the process of electrospray, either fibers or spherical droplets [46]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sample** & \(\delta_{D}\) & \(\delta_{P}\) & \(\delta_{H}\) & **Distance to PCL a** & **Solubility b** & **Reference** \\ \hline Acetic acid & 14.5 & 8.0 & 13.5 & 8.7 & good & [99] \\ Acetone & 15.7 & 5.3 & 11.7 & 5.7 & partial & [99] \\ Acetonitrile & 15.3 & 18.0 & 6.1 & 12.9 & partial & [102,103] \\ Aniline & 19.4 & 5.1 & 10.2 & 4.3 & good & [103] \\ n-Butyl acetate & 15.8 & 3.7 & 6.3 & 4.8 & bad & [99] \\ Chloroform & 18.2 & 6.3 & 6.2 & 1.9 & good & [104] \\ Cyclohexanone & 17.7 & 9.8 & 5.1 & 4.5 & partial & [105] \\ Dichloromethane & 17.8 & 3.1 & 5.7 & 3.7 & good & [104] \\ Diethylene glycol & 16.2 & 14.7 & 20.5 & 15.6 & bad & [106] \\ Dimethylacetamide & 16.8 & 11.5 & 10.2 & 6.1 & partial & [107] \\ Dimethylformamide & 17.4 & 13.7 & 11.3 & 8.3 & partial & [108] \\ Dimethyl sulfoxide & 18.4 & 16.4 & 10.2 & 10.6 & bad & [99] \\ Ethyl acetate & 15.8 & 5.3 & 7.2 & 4.0 & partial & [99] \\ Dichloroethane & 19.0 & 7.4 & 4.1 & 4.7 & good & [109] \\ Ethanol & 15.8 & 8.8 & 19.4 & 12.5 & bad & [99] \\ Ethylene glycol & 17.0 & 11.05 & 26.0 & 18.9 & bad & [103] \\ Formic acid & 14.3 & 11.9 & 16.6 & 12.5 & partial & [99] \\ Glycerol & 20.5 & 14.6 & 19.1 & 15.2 & bad & [110] \\ Methanol & 15.1 & 12.3 & 22.3 & 16.6 & bad & [108] \\ Methyl acetate & 15.5 & 7.2 & 7.6 & 4.5 & NT & [99] \\
1-Pentanol & 15.9 & 4.5 & 13.9 & 7.3 & bad & [104] \\
1-Propanol & 16.0 & 6.8 & 17.4 & 10.2 & bad & [99] \\ Tetrahydrofuran & 16.8 & 5.7 & 8.0 & 1.9 & good & [108] \\ water & 15.6 & 16.0 & 42.3 & 36.1 & bad & [111] \\ \(N\)-Methyl-2-pyrolidone & 18.0 & 12.3 & 7.2 & 6.2 & partial & [103] \\ Pyridine & 18.9 & 10.6 & 5.9 & 5.4 & good & [108] \\ Benzyl alcohol & 18.5 & 6.3 & 13.9 & 10.7 & good & [112] \\ Carbon tetrachloride & 17.8 & 0.0 & 0.6 & 9.5 & partial & [108] \\ Toluene & 18.0 & 1.4 & 2.0 & 7.6 & good & [108] \\ Benzene & 18.4 & 0.0 & 2.0 & 8.6 & good & [108] \\ Ethyl formate & 15.5 & 8.4 & 8.4 & 5.0 & NT & [99] \\ Methyl ethyl ketone & 16.0 & 9.0 & 5.1 & 5.2 & partial & [99] \\ Isopropyl acetate & 14.9 & 1.4 & 4.1 & 8.3 & NT & [99] \\
2-Butanol & 15.8 & 5.7 & 14.5 & 7.7 & bad & [99] \\
1-Butanol & 16 & 5.7 & 15.8 & 8.7 & bad & [99] \\ Isopropyl benzene & 16.2 & 7.0 & 0.0 & 8.4 & NT & [99] \\ Isopropyl alcohol & 15.8 & 6.1 & 16.4 & 9.4 & bad & [113] \\ Isobutanol & 15.1 & 5.7 & 15.9 & 9.6 & NT & [99] \\ Heptane & 15.3 & 0.0 & 0.0 & 11.1 & bad & [99] \\ Pentane & 14.5 & 0.0 & 0.0 & 11.8 & bad & [99] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Hansen solubility parameters of some common solvents and its solubility to PCL (part of the results obtained from swelling test and other part of results obtained from group distribution method). A higher entanglement among PCL chains indicates that the molecular structure of PCL chains is more condensed in electrospray droplets, and the size, and the morphology of the resulted particles are smaller and smoother, respectively. For the lower entanglements among PCL chains, the molecular structure of PCL chains is loose, and the morphology of the final products is porous (or wrinkled) [92]. Therefore, the distance from solvent to PCL is an indication of the solubility of solvent to PCL and influences the morphology and structure of electrospray particles. In can also be noticed that a high solubility is required to obtain high electrospray productivity, whereas a partial solubility is used for electrospinning process [120]. Binary or ternary solvent system is also used to dissolve PCL for an electrospray process. It exhibits greater potential and advantages in electrospray polymeric particles to provide adequate structure and morphology [121; 122], such as a porous morphology [49].