Maneuvering surface structures of polyvinylidene fluoride nanofibers by controlling solvent systems and polymer concentration

The surface evolution of fibers has been attracting great attention in many areas. In this work, we demonstrated the feasibility of directly electrospinning grooved and porous polyvinylidene fluoride fibers by varying polymer concentration and using both single/binary solvent systems. We discovered that grooved fibers can be generated from a variety of binary solvent systems, whereas porous fibers can be achieved using low boiling point solvent (LBPS) systems. The results indicated that the key factors for the formation of grooved fibers are the polymer concentration, the difference of evaporation rate (the difference of boiling points between each of the two studied solvents) between the two solvents, and the solvent ratio. While the polymer concentration, the presence of LBPS, and the solvent ratio are the decisive factors for the formation of porous structures. The formation mechanism of grooved fibers was attributed to void-based elongation, wrinkle-based elongation, and collapsed jet-based elongation. The mechanism for the formation of porous fibers was ascribed to the coexistence of both thermally induced phase separation and vapor induced phase separation. These structures can be used in different applications, such as harvesting energy and filtration. Importantly, we believe our work can serve as guidelines for the preparation of grooved and porous nanofibers through electrospinning.