Crosslinking of polyimide atomic-layer-deposited on polyethersulfone membranes for synergistically enhanced performances

Polyimide (PI) has been uniformly deposited and chemically crosslinked to form a hydrophilic and robust coating layer wrapping the skeleton of the macroporous polyethersulfone (PES) substrate membranes. PI is coated along all the exposed surfaces including the free surfaces and also the pore walls of the PES membranes by atomic layer deposition. The PI-deposited PES membranes are immersed in the excessive methanolic solution of ethylenediamine to initiate the crosslinking of PI chains. The crosslinked PES membranes exhibit synergistically enhanced performances in multiple aspects. They obtain enhanced hydrophilicity due to the formation of polar amide bonds. Control experiments on smooth PI films deposited on nonporous substrates reveal that crosslinking progressively increases the thickness of the PI films. Consequently, we are able to well control and tune the pore sizes by changing the crosslinking durations. The selectivity is enhanced by larger amplitude than the reduction of permeability as a result of reduced pore size and enhanced hydrophilicity after crosslinking. In addition, crosslinking also efficiently improves the thermal and mechanical stability and corrosion resistance of the PES membranes.