Microstructural design and control of funnel-like PES microfiltration membranes via the coupled RTIPS-VIPS technology

To address the challenges of insufficient permeability and long-term operational stability for microfiltration (MF) membranes in biopharmaceutical sterilization applications, in this study, a preparation process based on the coupling of reverse thermally induced phase separation (RTIPS) and vapor-induced phase separation (VIPS) was developed to fabricate the polyethersulfone (PES) MF membranes with a funnel-like pore structure, high surface porosity, and narrow pore size distribution. The effects of the temperature of the casting solution, ambient humidity and the exposure time on the membrane structure and performance were systematically investigated. The results indicated that as the temperature of the casting solution increased, the thickness of the loose layer for the membrane gradually increased, accompanied by significant enhancements in pore size, porosity, and pure water permeability (PWP). The PWP increased from 6634.3 to 9032.7 L m −2  h −1  bar −1 . The increase in humidity significantly enhanced the mechanical properties of the membranes (from 4.2 MPa for M 58 – 35-4 to 5.5 MPa for M 58 – 80-4 ) and simultaneously improved the rejection rate of E. coli and the flux retention rate (maintaining 68% after 3 h of operation, significantly higher than the 36% of the M-RTIPS membrane). Combined with thermodynamic analysis and molecular dynamics (MD) simulations, the “wet inverse heat synergistic induction” phase separation mechanism was revealed from the perspectives of free volume fraction (FFV) and mean squared displacement (MSD). This study provides a new strategy for fabricating high-performance MF membranes and offers a theoretical basis for efficient sterilization in the biopharmaceutical field.