Study on the formation and structural evolution of bead-on-string in electrospun polysulfone mats

Bead-on-string is a desirable morphology for some emerging applications of electrospun mats such as superhydrophobic surfaces. In this study, the bead-on-string morphology in electrospun polysulfone (PSU) mats was investigated and correlated with the solution concentration, voltage and feed rate. PSU/dimethylformamide solutions with different concentrations (4, 5.5, 7, 15, 18 and 20 wt% PSU) were electrospun at a constant feed rate (3.5 mL h(-1)) and voltage (15 kV). Critical chain overlap and entanglement concentrations were found to be 3.65 and 7.12 wt% PSU, respectively. The bead-on-string morphology was detected in the concentration range 7-18 wt% PSU, in close agreement with theoretical estimations. The evolution of the bead-on-string morphology in mats prepared from 15 wt% PSU solution and electrospun at three feed rates (i.e. 1.5, 2.5 and 3.5 mL h(-1)) and voltages (i.e. 12.5, 15 and 18 kV) were also studied. The results showed that the beads appear less in number as either the feed rate or the voltage increases. In addition, the morphology of the beads revealed a transition from a spherical to a spindle-like appearance with an increase in voltage. The effect of feed rate on bead geometry, however, was revealed to depend on the applied voltage. (c) 2020 Society of Chemical Industry