Porous polyacrylonitrile (PAN) ultrathin fibers with nanopore structures were prepared by electrospinning a ternary system of PAN/dimethyl sulphoxide (DMSO)/N

N'-dimethylformamide (DMF) using a water bath at 3℃.We investigated the effects of proportion of DMSO to DMF

collection medium

PAN concentration

applied voltage and needle to collector distance on the diameter and surface porosity of PAN ultrathin fibers.The optimum electrospinning parameters are given as PAN concentration of 15 wt%

DMSO/DMF proportion of 1 ∶1 (W/W)

applied voltage of 16 kV

needle to collector distance of 5 cm

solution flow rate of 0.7 mL/h

relative humidity of 40%~70% and room temperature of 25℃.The diameter

morphology and porosity of porous PAN ultrathin fibers were characterized by scanning electron microscope

showing the fibers

which were obtained under the optimum conditions

were porous throughout with a diameter ranging from 420 nm to 490 nm

an average diameter of 468 nm and surface porosity of 3.4%.The BET specific surface area was measured by nitrogen adsorption and desorption isotherms.It can reach 43.86 m2/g

which is 5 times higher than the theoretical surface area of smooth and nonporous 468 nm PAN fibers.Moreover

nonsolvent induced phase separation has been proposed to be the main mechanism for the formation of porous PAN fibers

which is confirmed by the ternary phase diagram of PAN/(DMSO+DMF)/H2O.