Abstract
Electrosprayed poly(caprolactone) (PCL) microparticles were produced using five solvents (ethyl acetate, acetone, anisole, glacial acetic acid and chloroform) under different PCL concentrations and operating parameters. Not only green and appropriate solvent for PCL electrospraying was pointed out, but also the effects of solution properties (surface tension, electrical conductivity, viscosity and vapor pressure) and operating parameters (flow rate, working distance and applied voltage) on the formation of electrosprayed particles were clarified. The formation and shape of Taylor cone during electrospraying was observed by high-speed images captured with a camera, and the size and morphology of electrosprayed particles were characterized by optical and scanning electron microscopies. It can conclude that the cone–jet range of applied voltage mainly depended on electrical conductivity, and an ideal Taylor cone was easier to form under high viscosity and low surface tension. Although high electrical conductivity was a contributor to fabricate tiny particles, it was easier to fabricate mono-dispersed microparticles under low electrical conductivity. The poly-dispersed distribution obtained with a high electrical conductivity converted into mono-dispersed distribution with the increasing of viscosity. Furthermore, the size of electrosprayed particles also correlated with the surface tension and vapor pressure of the solvent used. Ethyl acetate, due to mild electrical conductivity and surface tension, moderate viscosity and vapor pressure, is a green and suitable solvent for PCL electrospraying. Single pore PCL microparticles with smooth cherry-like morphology can be prepared from ethyl acetate. Finally, long working distance not only stabilizes the break-up of charged jet, but also promotes the evaporation of solvent.
Highlights
For the last few decades, electrospraying technique, as a novel electrohydrodynamic atomization process, has been widely used to prepare polymeric microspheres or microcapsules as well as further achieve their functional coatings on materials surface [1,2,3,4,5]
The use of surfactant and intensive stirring in emulsification method, which may break down the structure and properties of microcapsules, is avoided in the electrospraying process
Being different from complex coacervation, self-assembly and the emulsification method, the experimental setup and operations of electrospraying are easy to implement, and the emission of toxic substance and environmental pollution during electrospraying can be limited to the minimum
Summary
For the last few decades, electrospraying technique, as a novel electrohydrodynamic atomization process, has been widely used to prepare polymeric microspheres or microcapsules as well as further achieve their functional coatings on materials surface [1,2,3,4,5]. Compared with other common technologies to fabricate particles in the micro- or nanoscale from polymeric solution, including an emulsification method, spray drying, complex coacervation, self-assembly and flashing nanoprecipitation [6,7,8,9,10], electrospraying allows for overcoming the main drawbacks and limits them. The agglomeration of particles, wide particles size distribution and low encapsulation efficiency to active principle as main limitations coming from these technologies can be improved effectively in electrospraying process via the Coulombic repulsion among charged droplets and using. The particle size distribution of electrosprayed particles is mono-dispersed under optimal conditions, and the morphological and structural design of electrosprayed microparticles can carry out effectively via changing solution properties and operating parameters. Electrospraying is regarded as a green, rapid and efficient technology to design polymeric microparticles
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