Morphology Control And Mechanism Study Of Electrospraying And Electrospinning In Antisolvents

Electrospraying(ESP)/eletrospinning(ES) method is a novel processing technique to fabricate polymeric microspheres or micro/nanofibers from electrically charged liquid jets of polymer solutions or melts under high voltage electrostatic field.Recently, particles/fibers fabricated by electrospraying/Electrospinning have been widely used in energy chemical engineering, biological medicine, environmental science and national defense, etc. And, functional particles/fibers with controllable properties like size and morphology are attracting more and more researchers'attention. In this study, electrospraying and electrospinning are carried out in antisolvents. The morphology of particles/fibers products could be controlled through adjusting the properties of antisolvents. The study was listed below in detail:1. To prepare polymer particle and microporous membrane, for the first time carbon dioxide-expanded antisolvent was proposed as a new atmosphere with tunable properties for electrospraying, which offered an opportunity of control over the product morphology by manipulating the operating pressure by means of adjusting solvent evaporation / extraction and plasticization of this new atmosphere. The electrospraying of PLGA solution in acetone was conducted in different atmospheres including ambient air, ambient hexane, high-pressure carbon dioxide, and in carbon dioxide-expanded hexane, respectively. The product morphology was characterized by scanning electron microscope (SEM) and the morphological evolution mechanisms upon interplay of solvent extraction and polymer plasticization were presented.Finally, the Peclet n?mber of the electrospraying in different atmospheres were estimated and related to product morphology.2. To fabricate the polymer fibers and particleswith different morphologies including: smooth fiber and particle, coarse fiber and particle and so on, ethanol and ethanol/water mixture antisolvents were used as a new atmosphere for ESP and ES in ambient environment. The solvent extraction/evaporation of ESP and ES in antisolvents were both ethanol>ethanol/water (7/3)> ethanol/water(1/1)>air. When the solvent extraction was higher, the surface morphologies of fibers/particles became coarser and sometimes displayed the particle collapse phenomenon. In the ES process,with more additionof ethanol into the polymer solution, the diameter of product fiber in ambient air ES decreased and became more uniform. The fibers in antisolvents were more uniform than in air. In the ESP process, the particle size increased when the polymer solution concentraion was increased. And bead morpgology were obtained with adding more ethamol into polymer mother solution. In the ES and ESP process, the sizes of fibers/particles in antisolvents were larger than in air, the crystallinity were not significantly changed and the melt point increased slightly.3. PCL/DCM/DMF were used as the polymer mother solution for ES/ESP into ethanol or ethanol/water mixture antisolvents in ambient environment and all the products were bowl particles or fibers with collapse bead structure. With the increase in concentration of mother solution, the particles sizes became larger in all the different antisolvents. Bead morphology was obtained when the concentration of 10wt%PCL/DCM/DMF (3/1) solution was between ESP and ES. The bowl particles or fibers with collapse bead structure could become solid particles or fibers upon addition of NaCl into the ethanol/water antisolvent.The crystallinity of particles in antisolvent was not significantly changed and the melt point increased slightly.