Revealing the internal β-phase PVDF membrane fouling tendency using double layer piezoelectrics

Dissolved organic matter (DOM) is recognized as a crucial factor contributing to the irreversible fouling of ultrafiltration membranes. Quartz crystal microbalance with dissipation (QCM-D) offers insights into the kinetics of fouling layer formation and its structure in-situ on a model membrane. However, a clear correlation between the membrane fouling process and the adsorption-desorption results obtained from QCM-D has yet to be established. In this study, piezoelectric β-phase PVDF membranes were prepared, and their fouling behavior in response to three model compounds (humic acid (HA), dextran (DEX), bovine serum albumin (BSA), and their mixed solutions was examined. It was firstly proposed that the spin-coated model PVDF membrane surface exhibited a typical β-phase structure, characterized by regular undulations resulting from strong stretching effects. A novel double layer piezoelectric sensor, consisting of a β-phase layer over a piezoelectric quartz substrate, was designed for QCM-D analysis to assess the mass and stiffness variations of the absorbed DOM layer. The fouling tendency followed the order of BSA > Mixture > DEX > HA, with the foulant monomeric units having a similar molecular mass of around tens of kDa. Irreversible fouling resistance in series model as well as frequency drop in QCM-D were listed as indicators of irreversible fouling caused by foulant-membrane interaction, which realized a well-defined match for the first time.