Synthesis of Tunable Spongy PVDF Membranes for Water Treatment Applications

Functionalized membranes are gaining increased use in many applications and often it is desired for such membranes to have a maximum degree of functionalization. In this study, flat sheet poly(vinylidene fluoride) (PVDF) membranes are synthesized with a thick cross section and spongy interior morphology by an immersion precipitation phase inversion technique. This results in a greatly increased membrane interior surface area allowing for a high degree of membrane functionalization. Using dimethylformamide (DMF) as solvent and an elevated membrane casting temperature (35-40^oC) the equilibrium relationship between polymer and solvent is able to be controlled to create a thick and spongy membrane. Membrane morphology was examined using scanning electron microscopy (SEM) where a thick membrane top layer and open substructure were found. Membranes were functionalized in this study using poly(acrylic acid) (PAA) and it was found a higher degree of PAA functionalization was possible in spongy membranes over non-spongy membranes. The membrane flux can be modulated by pH variation. Spongy membranes have also shown highly enhanced divalent calcium ion pick up over non-spongy membranes. The iron nanoparticle functionalization capacity of these membranes is also being studied and it is expected that a high degree of membrane functionalization will be possible. Through this study, it has been shown that the synthesis of spongy PVDF membranes allows for increased functionalization with PAA allowing for tunable performance in any number of applications. This project has been supported by NIH-NIEHS-SRP, and by NSF EPSCOR program. Technical support of ULTURA Corporation is highly appreciated.