Influence of Ultrasonication Conditions on the Structure and Performance of Poly(vinylidene fluoride) Membranes Prepared by the Phase Inversion Method

The morphology and crystallization properties of poly(vinylidene fluoride) ultrafiltration membranes prepared by the phase inversion method were investigated under ultrasound-assisted conditions in a coagulation bath. All the membranes showed improved performance compared with that of the pristine membrane, including preferable morphology, higher porosity, and higher flux for water and a Rose Bengal (RB) aqueous solution. With an increase in the ultrasonic intensity, the flux of membranes for both water and RB aqueous solution increased gradually, while the rejection by all membranes was nearly 80%. The porosity was measured by the percentage water content. Phase separation was accelerated and macrovoids developed with an increase in ultrasonic intensity, resulting in an improvement in membrane porosity. The crystalline structure was assessed by wide-angle X-ray diffractometry and attenuated total reflectance Fourier transform infrared spectroscopy. It was also shown that the β crystalline phase was partly converted to the α crystalline phase in the ultrasound-assisted phase inversion process. Membranes prepared by ultrasound-assisted phase inversion exhibited elongation greater than that of the pristine membrane.