Poly(m-phenylene isophthalamide) (PMIA): A potential polymer for breaking through the selectivity-permeability trade-off for ultrafiltration membranes

The selectivity-permeability trade-off represents a limitation to the performance of ultrafiltration (UF) membranes. Theoretically, this trade-off is mainly determined by the pore structure, including the porosity, pore radius distribution and skin layer thickness. Benefiting from its high rigidity and high surface free energy, poly(m-phenylene isophthalamide) (PMIA) is proposed for preparing a high-performance UF membrane. In this work, PMIA membranes with various effective pore radii (6.58 nm, 6.84 nm and 9.28 nm) were fabricated via nonsolvent-induced phase separation (NIPS). Through selectivity-permeability analysis, the PMIA membrane was found to break through the trade-off between selectivity and permeability. Compared with other UF membranes, the PMIA membrane exhibited a high porosity, narrow pore radius distribution and excellent hydrophilicity, leading to its high performance in the filtration process. This phenomenon could probably be attributed to the high rigidity, which confined the motion of the PMIA chain to suppressing pore collapse during pore formation, as well as to the high surface free energy that caused the hydrophilicity. All of these results clearly indicated that PMIA might be the most appropriate polymer for fabricating the UF membrane.