Hollow fiber membranes fabricated via dry/wet phase inversion method usually have two dense skin layers

which will increase its resistance of mass transport as a support membrane.It is necessary that the dense skin layer of support membrane has been eliminated to improve separation performance of composite membrane.The excellent chemical resistance of poly(vinylidene fluoride) (PVDF) to many acids and alkalis has made it as an attractive membrane material

and then it’s often fabricated as porous hollow fiber membrane by phase inversion.In the process

the formation of the skin layer is due to the rapid exchange between solvent and coagulation

so many attempts have been made to slow it

so as to control the formation of the skin layer.In this paper

it has been found that the fabrication progress becomes unstable

and the membrane prepared has noncircular lumen

when the “weak" or “soft" coagulation is used.To increase the fabrication solution stability during membrane formation

dope viscosity was focused in this experiment.Dimethyl acetamide (DMAc) was used as solvent as well as internal coagulant

and the additives including LiCl

water and surfactant Span were chosen to investigate their effect on the viscosity of the fabrication solution.The dope viscosity will greatly increase after adding LiCl

while the variety of dope viscosity is unconcerned in the fabrication solution concentration as adding water.The homogenization and stability of the fabrication solution are improved by adding Span

and the viscosity increases at the same time.Without increasing PVDF concentration

the stability of the nascent membrane was improved by increasing the fabrication viscosity.The PVDF hollow fiber membrane with the structure of single outer skin layer and finger-like pore through the cross_section

has been successfully fabricated.The mean pore radius and water flux of the single skin hollow fiber membrane were greatly improved.