Effect of Vapor Phase Infiltration on Mechanical and Chemical Properties of Polyethersulfone Membranes

The incorporation of metal oxides into polymer membranes via vapor phase infiltration (VPI) can alter their chemical stability and mechanical properties. Here, we show how key VPI process parameters, such as reactant exposure times and process cycles, can affect the infiltration depth and loading of inorganic reactants within polymers, influencing the extent of these alterations. Polyethersulfone (PES) membranes were treated with trimethylaluminum and water using VPI under short and long reactant exposure times, which resulted in alumina infiltration depths ranging from approximately 20 to 350 nm. Mechanical properties─including burst pressure, tensile strength, elongation at break, and elastic modulus─were correlated with alumina distribution. Membranes with deeper infiltration from 300 s reactant exposures showed only a modest decrease in burst pressure (250 ± 4 kPa) compared to pristine membranes (296 ± 9 kPa), whereas those with shallow infiltration from 0.25 s exposures exhibited a significant reduction (53 ± 11 kPa). Furthermore, elastic modulus increased substantially after VPI, from 90 ± 10 MPa in pristine membranes to 381 ± 24 MPa (0.25 s exposure) and 186 ± 9 MPa (300 s exposure). These modulus changes were further analyzed using theoretical models, such as the rule of mixtures and Gibson-Ashby formulations. The chemical stability of VPI-treated PES membranes was then evaluated to explore the trade-off between mechanical resilience and chemical resistance. Results suggest that deeper and more uniform alumina infiltration improves chemical stability while maintaining ductility. These findings provide insights for optimizing VPI modification for advanced membrane separation processes.