Core/shell polyacrylonitrile(PAN)fibers with an outer diameter of 3 μm were prepared by coaxial electrospinning using silicon oil as the core and PAN solution as the shell.After oxidation-stabilized and high-temperature pyrolyzed

some hollow carbon fibers with an outer diameter of 1 μm can be obtained.Morphologies and structural changes of the fibers were characterized by scaning electron microscopy(SEM)and Fouriertransform infrared (FTIR) spectroscopy respectively.Effects of coaxial spinneret and feeding rate ratio of the inner and the outer liquids (Vin/Vout) were studied on the formation of the coaxial fibers.Results showed that the net length of the core nozzle over the shell nozzle

Zp

affected the formation of the coreshell jets greatly:when Zp was about half of the shell nozzle radius (rout)

a coaxial jet could be obtained on the tip of the coaxial spinneret; but if Zp increased larger than 0.7 rout

the shell fluid was splitted into multiple jets.In addition

feeding rate ratio also had a great influence.Coaxial fibers could be obtained when Vin/Vout=1

whereas either porous fibers were obtained whenVin/Vout=0.5

or a single PAN solution jet and silicon oil droplets were obtained when Vin/Vout=2.