The effects of additive, Tween-20, on the morphology and ultra-filtration performance of the PVDF membranes formed by isothermal immersion precipitation from the Tween-20/water/TEP/PVDF system were investigated. High resolution FESEM imaging indicates that the membranes׳ bulk constituted of interlinked crystalline particles, whose shapes change from more sheaf-like to more stick-like as larger amounts of Tween-20 were initially added into the dope. Introduction of Tween-20 caused formation of nano-pores on the top surfaces of the membranes and micron-sized columnar voids underneath the top skin layer. Some small amounts of Tween-20 may reside in the formed membrane if the nascent membrane has not been carefully washed. Presence of Tween-20 in the membrane was analyzed by water contact angle measurements, Fourier Transform Infrared-Attenuated total reflection spectroscopy (FTIR-ATR), Nuclear Magnetic Resonance (NMR), and X-ray Photoelectron Spectroscopy (XPS). Furthermore, water flux and blue dextran filtration experiments were carried out to illustrate the potential applications of the membranes in fine separation processes.
