Construction of hierarchical structures by electrospinning or electrospraying

To expand the application of electrospun fibers or electrosprayed beads, micro-nano hierarchical structures of polystyrene (PS) have been constructed through the adjustment of solvent, polymer concentration, environment humidity, electrospinning temperature, etc. Primary structures, such as fibers, beads and bead-on-string structure, as well as secondary structures, such as nanopores, nanopapilla and net-work structure, have been constructed. Solvent plays an important role in the construction of both primary structures and secondary structures. By using N,N-dimethylformamide (DMF), tetrahydrofuran (THF) and mixed solvent of DMF/THF, the micro-nano hierarchical structures can be controlled. Humidity is a key factor to the construction of secondary structures. The obtained fibers or beads have smooth surface at low humidity. While at high humidity, secondary structures tend to appear. For the PS/DMF system, vapor-induced phase separation may be the most pertinent mechanism to explain the formation of secondary structures. While for the PS/THF system, breath figure theory can explain the formation of uniform nanopores properly.