Variation of free volume and thickness by high pressure applied on thin film composite reverse osmosis membrane

Analytical technologies for polymeric membranes, including positron annihilation lifetime spectroscopy (PALS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), were employed to understand the origin and harmful effects of thin film composite (TFC) reverse osmosis (RO) membrane compaction. Although no variation in water flux exceeding 10% from the initial flux was observed under all compaction pressures, the hydraulic pressure induced by the high-pressure pump caused a rapid contraction of the free volume and thickness of the TFC RO membrane. In particular, due to the viscoelastic polymer properties of the active layer, a reduction of approximately 15% free volume and 48% thickness was observed at a compaction pressure of 60 bar. Consequently, the analytical procedures can provide a better understanding of membrane compaction during pressurized membrane processes and strategic development to reduce the harmful effects of membrane compaction. [Display omitted] •TFC RO membrane compaction was fundamentally analyzed by PALS and ToF-SIMS.•Compaction at high applied pressures reduced water permeability in the RO membrane.•The greatest effect of compaction was observed in the active layer of RO membrane.•The applied high pressure reduced the free volume and thickness of the active layer.•Proposed analyses could estimate the harmful effects on the RO membrane compaction.