Electrospraying of polymer solutions for the generation of micro-particles, nano-structures, and granular films

Identifier:  TDX:2227

Handle: https://hdl.handle.net/20.500.11797/TDX2227

Authors:  Bodnár, Eszter

Abstract:
A study has been made of the mechanisms underlying the formation of polymeric microparticles and of their granular films, by drying of electrospray microdroplets. The study is focused on different solutions of three water-insoluble polymers: polymethyl(methacrylate), polystyrene, and ethyl cellulose. The drying of such electrosprays result in diverse particle morphologies, which have been determined by scanning electron microscopy, and have been characterized as a function of the solvent, polymer concentration, polymer molecular weight, and ambient relative humidity. The morphologies obtained include a variety of globular and filamented particle structures, which, at elevated relative humidity, can develop porosity. These morphological features have been explained using qualitative models involving fluid dynamic and phase separation phenomena which are known to occur in closely related systems. One of the key fluid dynamic phenomena involved is the coulombic instability of electrically charged droplets. In addition, the non-solvent interaction of water on the precipitation of the polymer can lead to porous textures on the particles surfaces. The different kinds of textures have been explained by reference to breath-figure formation (BFF) and vapor induced phase separation (VIPS) phenomena. We have also studied the growth of the granular films of such polymer particles. We show that the electrical charge transported by the particles to the film have a strong influence on the film growth dynamics. The better understanding of the mechanisms studied in this thesis, should help design new manufacturing processes of particles and coatings based on electrospray.