# Influence of Solvent Selection in the Electrospraying Process of Polycaprolactone
## 2 Electrospraying Technology
### Experimental Apparatus  
In general, the setup of electrospraying mainly composes by syringe, syringe pump, nozzle, high-voltage generator, and collector (Figure 2a). In order to facilitate observation and analysis, light source and high-resolution camera connected with a computer are also often used in the process of electrospraying [38]. At first, electrospraying solution is added into a syringe and further transported to the nozzle under an adjustable flow rate via syringe pump. The nozzle is linked with one end of the high-voltage generator (mostly positive), and the other end of the high-voltage generator is connected to the collector (often grounded or more rarely negatively charged). The distance between the tip of the nozzle and collector usually range from a few centimeters to several tens of centimeters. Due to the strong electric field between nozzle and collector and the Coulomb repulsions, the electrospraying solution will be stretched and further dispersed into smaller droplets, which are ejected from the tip of Taylor cone. During the flight of droplets to the collector, solvents in these droplets will evaporate, and solid particles can be obtained in collector finally. Further, if needed, these particles could be placed into a vacuum oven to remove the residual solvent. Sometimes, in order to further stabilize the process of electrospraying and cone-jet, a ring-shaped electrode is placed between the nozzle and the collector [87; 88]. The strength of electric field between the nozzle and ring-shaped electrode and the strength of electric field between ring-shaped and collector can be effectively adjusted via controlling the distance among them. Meanwhile, the size and distribution of electrosprayed particles will change obviously with the changing of the electric field among nozzle, ring-shaped electrode, and collector. With increasing demands for diversified structures of polymeric particles in the biomedical field, there are some changes and innovations in the setup of electrospraying to prepare polymeric particles with novel structure and morphology for satisfying these demands. Major innovations and changes focused on the structure of nozzle and collection method. According to the position of the capillary in the nozzle, the nozzles used in electrospraying divide into two categories, coaxial-capillary nozzle, and parallel-capillary nozzle. Common coaxial-capillary nozzles include two or three capillaries coaxial nozzle (Figure 2b,c). Single-shell capsules and double-shell capsules can be fabricated by using  
Figure 2: Common examples of electrospraying apparatus, (**a**) single-capillary electrospraying, (**b**) double-capillaries coaxial nozzle, (**c**) triple-capillaries coaxial nozzle, (**d**) double parallel-capillaries coaxial nozzle, (**e**) double parallel-capillaries coaxial nozzle with static micromiker, (**f**) double-capillaries coaxial nozzle with grooved structure, (**g**) multiplexed electrospraying setup with several electrospray sources operating in parallel and an extractor, (**h**) electrospraying via a nozzle-ring setup inside a glass chamber under air flow, and (i) electrospraying device with liquid bath collector (modified from [37, 40, 65, 89, 90, 91, 92, 93, 94]). these nozz in electrospraying. The core material is added into the inner capillary and shell material is added into the outer capillary. A separate syringe pump controls the flow rate of liquid in each capillary. As for parallel-capillary nozzle, it consists of some parallel inner capillaries and an outer capillary (Figure 2d). [PERSON] et al. first time adopted these nozzles to prepare a single microcapsule with multiple active substances embedded [89]. They found that each component in microcapsule is inhibited into individual compartments free of contact with others. If two active substances in microcapsules need to be mixed, the nozzle with static micromixer (Figure 2e) can be used during electrospraying. [PERSON] et al.