Hybrid organic-inorganic isoporous membranes with tunable pore sizes and functionalities for molecular separation

Block copolymers (BCPs) are considered promising materials for various membrane applications ranging from water treatment to protein separation due to their ability to self-assemble into highly ordered structures with uniform pore size and high pore density. Typically, the pore’s size and surface interactions are controlled by the BCP chemistry. However, simultaneous control over both properties is difficult to achieve. In particular, reaching nanometric pores which will allow for molecular separation through the BCP chemistry is considered a major challenge.

In this study, we tailor the size and chemistry of BCP based ultrafiltration membranes by selectively growing metal oxides within and on the pores. Poly (styrene-b-4-vinyl pyridine) (PS-b-P4VP) was used to create ultrafiltration membranes in a process combining self-assembly with non-solvent induced phase separation (SNIPS). This results in one integral but asymmetric membrane, with ordered pores at the top of the membrane and sponge-like mechanically robust support layer at the bottom of the membrane. Sequential infiltration synthesis (SIS), an atomic layer deposition-based technique that enables selective growth of metal oxides inside the polar domains of BCP, was used to grow Al2O3 inside the P4VP domains of the BCP films. By incorporating metal oxides in the pores, the pore size can be reduced. By modifying the number of SIS cycles and/or the metal oxide we use, we can achieve control over the pore size while laying grounds for further membrane functionalization.

Functionality is achieved via straightforward scalable gas/liquid-solid interface reactions, where the hydrophilicity/hydrophobicity of the membrane is significantly changed by introduction of functional groups. The functionalized membranes reveal a superior selectivity and permeability to separate small organic molecules and fractionate similar-sized proteins based on size, charge and hydrophobicity.

This demonstrates the great potential of combining BCP and metal oxide growth for high-performance membranes for molecular separation. These membranes could be used in chemical and pharmaceutical processing as well as in other nanofitlation applications.