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. • 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.