PLLA ultrafine fibers with mesopores of 30~150 nm were prepared by electrospinning.Their surface morphology was studied using scanning electron microscopy (SEM).The fiber diameter and morphology could be controlled by adjusting the composition ratio of the dichloromethane (DCM)/N

Ndimethylformamide (DMF) solvent mixture

PLLA concentration and electric filed.Accordingly

fibers with varied surface structure such as smooth surface

shallow pits

or deep pores were obtained.Under optimal electrospinning conditions of DCM/DMF 4∶1

PLLA concentration of 9 wt%

electric field 1 kV/cm and relative humidity of 52%

dense mesoporous PLLA ultrafine fibers with mean pore diameter of 150 nm were fabricated.Moreover

it showed 3-dimensional interconnected porestructure throughout PLLA ultrafine fibers.Most pores were elongated along the fiber axis due to the stretching in the process of electrospinning.The characteristic porous PLLA fiber was formed by a combination of thermal induced phase separation (TIPs) with water assisted breath figure mechanisms

because of the sharp temperature drop caused by the quick solvent evaporation in the electrospinning process.The PLLA fibers with shallow pits or pores of 80 nm in diameter showed water contact angle of 104°，whereas the fibers with deep pores of 150 nm in diameter were highly hydrophobic with water contact angle up to 1466°.The hydrophobic fibrous mats could quickly absorb oil

90 g/g in 90 s and 145 g/g in 25 min.Their maintaining capacity of oil absorption was 90%.