Stretching-induced orientation of polyacrylonitrile nanofibers by an electrically rotating viscoelastic jet for improving the mechanical properties

An additional centrifugal field applied to an electrostatic field in a novel electrospinning technique was proposed in this study. An additional centrifugal field can not only remove bending instability of electrically charged liquid jets during the electrospinning process but can also fabricate aligned and molecularly oriented nanofibers. The results indicated that combining a strong stretching force from an additional centrifugal field and an electrostatic field can be used to align polymer chains parallel to the nanofiber axis, producing polyacrylonitrile (PAN) nanofibers with superior molecular orientation and mechanical properties. The optimal stretching force of an electrically rotating viscoelastic jet was obtained from high-speed videography and dimensionless groups (Re, We, and Oh numbers) analysis. The dichroic ratio (D) was 0.78, and the chain orientation factor (f), measured via Polarized FT-IR was 0.21. These measurements indicated an increase in the molecular orientation for the fabricated PAN nanofibers via the optimal stretching force. The elastic modulus of PAN nanofibers with f = 0.21 was 6.29 GPa and 4.55 GPa when measured by atomic force microscopy (AFM) and nanoindenter experiments, respectively. These results demonstrated that superior mechanical properties of PAN nanofibers could be improved by conducting the proposed electrospinning technique. Furthermore, carbon nanofibers produced from the optimal PAN nanofibers through the proposed method could potentially be applied for the reinforcement of composites.