Highly selective isoporous block copolymer membranes with tunable polyelectrolyte brushes in soft nanochannels

We used partial crosslinking of the pore-forming block of quaternized PS-b-P4VP integral asymmetric isoporous membranes as a tool to control the effective pore size in aqueous and alcoholic media. A versatile top-down membrane post-modification approach using a combination of difunctional and monofunctional alkyl halide was employed to obtain well-defined nanochannels containing polyelectrolyte brushes. Mild and scalable gas-solid reactions were used for the membrane post-modification. The permeance of the modified membranes changed systematically over a wide range, proving the potential of using the membrane post-modification technique to tailor the pore size from ultrafiltration to nanofiltration regime. Using a membrane post-modification technique, for the first time a series of integral asymmetric isoporous membranes having equal charge density but distinct effective pore size was successfully prepared. The separation performance based on size and charge is demonstrated by separating 1-2 nm organic molecules (having molecular weights in the range of 248-480 g mol(-1)) with excellent selectivity and permeance. For example, one of the prepared membranes showed a 2.4 times higher retention of methylene blue (MB+, 319.85 g mol(-1)) than chrysoidine G (CG+, 248.71 g mol(-1)) from an aqueous feed solution containing equimolar MB+ and CG + while the permeance was 134 Lm(-2)h(-1)bar(-1).

Automated summary

In this study, a series of porous membranes with different effective pore sizes were successfully prepared using a membrane post-modification technique. The excellent separation performance was demonstrated by separating organic molecules of 1-2 nm in size.