Highly permeable nanoporous block copolymer membranes by machine-casting on nonwoven supports: An upscalable route

Porous block copolymer separation membranes for 21st century sanitation and hygiene

Removing hazardous particulate and macromolecular contaminants as well as viruses with sizes from a few nm up to the 100 nm-range from water and air is crucial for ensuring sufficient sanitation and hygiene for a growing world population. To this end, high-performance separation membranes are needed that combine high permeance, high selectivity and sufficient mechanical stability under operating conditions. However, design features of separation membranes enhancing permeance reduce selectivity and vice versa. Membrane configurations combining high permeance and high selectivity suffer in turn from a lack of mechanical robustness. These problems may be tackled by using block copolymers (BCPs) as a material platform for the design of separation membranes. BCPs are macromolecules that consist of two or more chemically distinct block segments, which undergo microphase separation yielding a wealth of ordered nanoscopic domain structures. Various methods allow the transformation of these nanoscopic domain structures into customized nanopore systems with pore sizes in the sub-100 nm range and with narrow pore size distributions. This tutorial review summarizes design strategies for nanoporous state-of-the-art BCP separation membranes, their preparation, their device integration and their use for water purification.

Next-Generation Ultrafiltration Membranes Enabled by Block Polymers

Reliable and equitable access to safe drinking water is a major and growing challenge worldwide. Membrane separations represent one of the most promising strategies for the energy-efficient purification of potential water sources. In particular, porous membranes are used for the ultrafiltration (UF) of water to remove contaminants with nanometric sizes. However, despite exhibiting excellent water permeability and solution processability, existing UF membranes contain a broad distribution of pore sizes that limit their size selectivity. To maximize the potential utility of UF membranes and allow for precise separations, improvements in the size selectivity of these systems must be achieved. Block polymers represent a potentially transformative solution, as these materials self-assemble into well-defined domains of uniform size. Several different strategies have been reported for integrating block polymers into UF membranes, and each strategy has its own set of materials and processing considerations to ensure that uniform and continuous pores are generated. This Review aims to summarize and critically analyze the chemistries, processing techniques, and properties required for the most common methods for producing porous membranes from block polymers, with a particular focus on the fundamental mechanisms underlying block polymer self-assembly and pore formation. Critical structure-property-performance metrics will be analyzed for block polymer UF membranes to understand how these membranes compare to commercial UF membranes and to identify key research areas for continued improvements. This Review is intended to inform readers of the capabilities and current challenges of block polymer UF membranes, while stimulating critical thought on strategies to advance these technologies.

Co-Casting Highly Selective Dual-Layer Membranes with Disordered Block Polymer Selective Layers

Highly selective and water permeable dual-layer ultrafiltration (UF) membranes comprising a disordered poly(methyl methacrylate-stat-styrene)-block-poly(lactide) selective layer and a polysulfone (PSF) support layer were fabricated using a co-casting technique. A dilute solution of diblock polymer was spin coated onto a solvent-swollen PSF layer, rapidly heated to dry and disorder the block polymer layer, and subsequently immersed into an ice water coagulation bath to kinetically trap the disordered state in the block polymer selective layer and precipitate the support layer by nonsolvent-induced phase separation. Subsequent removal of the polylactide block generated porous membranes suitable for UF. The permeability of these dual-layer membranes was modulated by tuning the concentration of the PSF casting solution, while the size-selectivity was maintained because of the narrow pore size distribution of the self-assembled block polymer selective layer. Elimination of the thermal annealing step resulted in a dramatic increase in the water permeability without adversely impacting the size-selectivity, as the disordered nanostructure present in the concentrated casting solution was kinetically trapped upon rapid drying. The co-casting strategy outlined in this work may enable the scalable fabrication of block polymer membranes with both high permeability and high selectivity.

Nanoporous block copolymer membranes immobilized with gold nanoparticles for continuous flow catalysis

Nanoporous polymers with functionalizable surfaces are desired in the preparation of reactors for continuous flow catalysis.