Anti-fouling piezoelectric PVDF membrane: Effect of morphology on dielectric and piezoelectric properties

Piezoelectric membrane serves as an alternative to vibratory shear-enhanced process, which potentially offers lower cost of operation as the source of agitation is the membrane itself. The effect of morphology on dielectric and piezoelectric properties of polyvinylidene fluoride (PVDF) membranes prepared via non-solvent induced phase separation method was investigated. The membranes were fabricated using different solvents: N,N-dimethylformamide (PVDF-DMF), 1-methyl-2-pyrrolidinone (PVDF-NMP) and triethyl phosphate (PVDF-TEP). Dielectric strength analysis and piezo-response force microscopy (PFM) revealed that PVDF-DMF, displaying finger-like morphology, presented highest dielectric strength and desired piezoelectric properties. The presence of macrovoids in PVDF-NMP resulted in weak dielectric strength. Electrical poling was performed, enhancing the piezoelectric properties of membranes. No noticeable change in microstructure was observed for PVDF-NMP after poling. However, cross-section morphology of PVDF-DMF visibly changed from finger-like to drop-like cavities. Infrared (IR) spectroscopy and PFM showed improvements in fraction of β phase and piezoelectric coefficient d₃₃ after poling. Cross-flow filtration experiments using colloidal silica were performed to investigate effect of electrical signal (10 Vpp, 500 Hz) on the membranes. It showed negligible effect on performance of unpoled PVDF-DMF, while 46% increase in critical flux and 66% reduction in transmembrane pressure increase (dTMP/dt) was observed for poled PVDF-DMF under electrical signal.