Accurately controlling the hierarchical nanostructure of polyamide membranes via electrostatic atomization-assisted interfacial polymerization

Abstract

Interfacial polymerization is a classical method for the preparation of thin-film composite (TFC) membranes. However, facile and controllable fabrication remains a grand challenge. Here, a dual-needle electrostatic atomization strategy is presented to atomize aqueous and organic phases into droplets respectively, and then a polymerization reaction occurs at interfaces. This method shows excellent controllability over the membrane nanostructure: the monomer ratio determines compactness and the monomer amount governs thickness. Particularly, a hierarchically structured IP layer is developed by regulating the monomer ratio, where the loose layer, a low-resistance region, supports the formation of an ultrathin dense layer for rejection. And the hierarchical nanostructure is proved by positron annihilation spectroscopy, CO₂ adsorption, etc. We demonstrate that an IP layer with a 13.8 nm-thick dense layer readily realizes ultrafast solvent permeance (56.9 and 23.7 L m⁻² h⁻¹ bar⁻¹ for acetone and water, respectively) and complete rejection for acid yellow 14 (1.9 nm). Such a performance is superior to that of most reported TFC membranes and overcomes the general permeation–rejection trade-off effect. Moreover, this hierarchically structured membrane displays excellent operating stability, pressure stability and cycle stability, especially solvent resistance over 30 days. Briefly, such a strategy endows the membrane with accurate regulation from chemical components to the physical structure, paving the way for the design of next-generation TFC membranes.