Thermodynamic Studies on Polyvinylpyrrolidone Solution Systems Used for Fabrication of Electrospun Nanostructures: Effects of the Solvent

In this research, we investigate the influence of polyvinylpyrrolidone (PVP) solution systems on the morphology of the PVP nanofibers fabricated by electrospinning of PVP solutions prepared in different organic solvents, including ethanol (EtOH), propanol (PrOH), chloroform, N-methyl-2-pyrrolidone (NMP), and N,N-dimethylformamide (DMF) and then compared with the experimental results. First, by considering the electrospun solutions behavior, the thermodynamic studies were evaluated then Hansen solubility theory was applied to select the desirable solvent systems. The dissolving power of the solvents for PVP was obtained in the following order: DMF > NMP >> chloroform > PrOH > EtOH. It seems that every solvent, which is able to dissolve PVP polymer, shows different spinning characteristics under identical conditions of processing parameters. By using PrOH, chloroform, and NMP solvents, electrospun nanofibers' average diameter was decreased intensively but at the same time beads formation was observed. We investigated that EtOH was a desirable solvent for PVP to fabricate fibers with z micrometer diameter distribution, but because of its low dissolving power it is suitable for microfiber synthesis with the electrospinning process. Based on the Hansen theory and experimental results, the PVP/DMF solutions showed desirable characteristics for the electrospinning system. Furthermore, the PVP nanofiber's uniformity of the PVP/DMF solution was higher than other solvent systems, which mean that fiber diameter distribution is scanty than others. Finally, it has been demonstrated that with an appropriate solvent the nanofiber diameter distribution and formation of beads can be controlled by Hansen theory.