Study on the interfacial activation of dual surfactants in the process of forming porous membranes

Abstract

In order to regulate the microstructure of separation membranes and further investigate the mechanism of membrane preparation. Polyvinylidene fluoride (PVDF) hollow fiber membranes were fabricated by NIPS using dual surfactants (Span80 and Tween80) as the additive. Exactly, the dual surfactants have the specific value of Hydrophilic-Lipophilic Balance (HLB). Here we evaluated the Hydrophilic-Lipophilic Balance offset value (ΔHLB) on the membrane relative properties such as the pure water flux, SEM etc. As results indicated, in the membrane preparation process of NIPS, the surfactant could activate the interface of polymer concentrated phase when the casting dope transits from the stable region to the unstable region. Also, when the value of HLB approached to 10, the interfacial activation of the dual surfactants was obvious, eventually leading to more pores on the skin layer. Meanwhile the membrane intrinsic resistance was the lowest. They are also featured by the most probable aperture moving toward the maximum pore size. Most importantly, compared to the separation membrane without the surfactant, the pure water flux increased by 277%, reaching up to 1015L/(hm2). This research introduces a new pore-making strategy of the surfactant interfacial activation on polymer concentrated phase, which involves a novel film-forming mechanism in NIPS.