# Influence of Solvent Selection in the Electrospraying Process of Polycaprolactone
## 3 Selection of Solvent Systems Used in PCL Electrospraying
### Solution Properties for Tailoring Characteristics of Electrosprayed PCL Particles
#### 3.3.3 Morphology
Besides, when different non-solvents with different physico-chemical properties (surface tension, viscosity, and vapor pressure) are used as the collection medium, the morphology of the collected particles is different governed by droplet deformation, their solidification, and the solvent diffusion [152; 154]. For example, [PERSON] et al. have observed that PCL particles with ellipsoidal macroporous (methanol), continuous and dense pores (ethanol), flower-shaped surface (propanediol-1,2), uniform spherical pores (tetraethyl orthosilicate) and pod-shaped (n-butanol) can be produced in sequence when these different non-solvents are used as collection medium (Figure 7) [152]. Also, as the surface tension of the collection liquid increases and the evaporation rate decreases, the shape of the droplets sprayed in the bath changes from spherical to flat. Besides, PCL thin films with different morphologies and textures are also obtained from electrospray coating, mainly when nonsolvent systems were used to dissolve PCL [151; 155]. Thus, the use of 2-ethoxy1 acetate (2 EEA), a nonsolvent at room temperature, and which partially solubilizes PCL at 30 \({}^{\circ}\)C lead to the obtaining of electrospun fibers with electrospray relics (PCL thin films with texture) [146]. [PERSON] et al. characterized the particle morphologies prepared by different electrospray solutions of polycaprolactone in chloroform [92]. Depending on the polymer concentration, microsphere or flattened particles were obtained in the case of higher and lower polymer concentration, respectively. The polymer concentration affects the solvent evaporation rate and chain polymer entanglement during the droplet flying process. Thus, a low polymer concentration leads to incomplete solvent evaporation, and recovered particles are still wet, or the PCL macromolecular chains are partially dissolved at the collector surface. The drying stage induces the formation of heterogeneous, semisolid, and flattened particles. They also denoted that this morphology was a consequence of fewer entanglement possibilities for polymer chains in the concentration range from 5 to 7.5 wt.%. Also, the morphology of electrospray particles also depends on environmental parameters (humidity, temperature, and atmospheric pressure) [49; 156; 157]. In general, the increase in relative humidity (humid atmosphere) leads to an increase in the number, diameter, shape, and distribution of pores on the surface of particles. Besides, the boiling point of the solvent and its evaporation rate are also correlated with atmospheric pressure. The increase in atmospheric pressure leads to  
Figure 7: SEM images of PCL-dichloromethane (DCM) microparticles (MPs) collected in the different organic solvents (non-solvents): (**a**) methanol; (**b**) ethanol; (**c**) 1,2-propanediol; (**d**) n-butanol; (**e**) tetraethyl orthosilicate. (**a\({}^{\prime}\)-e\({}^{\prime}\)**) High-magnification images showing the surface detail of the same porous MPs from (**a–e**), respectively (reprinted with permission from [152]). an increase in the boiling point of the solvent and a decrease in its evaporation rate. Therefore, electrospray particles with a smooth and non-porous structure can be obtained with increasing atmospheric pressure. On the contrary, with the decrease in atmospheric pressure, the morphology of atomized particles becomes irregular and porous.