Fit-for-purpose block polymer membranes molecularly engineered for water treatment

Abstract

Continued stresses on fresh water supplies necessitate the utilization of non-traditional resources to meet the growing global water demand. Desalination and hybrid membrane processes are capable of treating non-traditional water sources to the levels demanded by users. Specifically, desalination can produce potable water from seawater, and hybrid processes have the potential to recover valuable resources from wastewater while producing water of a sufficient quality for target applications. Despite the demonstrated successes of these processes, state-of-the-art membranes suffer from limitations that hinder the widespread adoption of these water treatment technologies. In this review, we discuss nanoporous membranes derived from self-assembled block polymer precursors for the purposes of water treatment. Due to their well-defined nanostructures, myriad chemical functionalities, and the ability to molecularly-engineer these properties rationally, block polymer membranes have the potential to advance water treatment technologies. We focus on block polymer-based efforts to: (1) nanomanufacture large areas of highperformance membranes; (2) reduce the characteristic pore size and push membranes into the reverse osmosis regime; and (3) design and implement multifunctional pore wall chemistries that enable solute-specific separations based on steric, electrostatic, and chemical affinity interactions. The use of molecular dynamics simulations to guide block polymer membrane design is also discussed because its ability to systematically examine the available design space is critical for rapidly translating fundamental understanding to water treatment applications. Thus, we offer a full review regarding the computational and experimental approaches taken in this arena to date while also providing insights into the future outlook of this emerging technology.

Structure of Nonsolvent‐Quenched Block Copolymer Solutions after Exposure to Electric Fields during Solvent Evaporation

“…The resulting membrane exhibits a selective surface layer of a well‐ordered nanoporous morphology, where the subjacent spinodal substructure forms a supporting layer. These type of membranes are very interesting for ultrafiltration purposes, as the nanoporous surface offers the possibility of highly size selective separation . The permeability is mainly affected by the selective layer, as the resistivity of the coarsened substructure is much smaller.…”

Nanostructure stability and swelling of ternary block copolymer/homopolymer blends: A direct comparison between dissipative particle dynamics and experiment

“…Monomer incompatibilities drive unlike blocks to minimize their contact, but the presence of the covalent bond prevents macroscopic phase separation so that BCPs self‐assemble into a variety of nanoscale morphologies to minimize their frustration . The ability to precisely control BCP domain sizes is critical for many applications, including advanced lithography, nanoporous membranes, and biological templating . Pure BCP feature sizes are dictated by degree of polymerization ( N BCP ), architecture, relative block sizes, and block incompatibilities as captured by the Flory–Huggins interaction parameter ( χ ).…”

Ion separations with membranes

“…Block copolymers offer an alternative method for creating uniform pores in membranes, but typical pore diameters are much larger than hydrated ion diameters. [158,161] We should note that perhaps the most impressive ion separations occur in natural protein channels. These systems combine exquisite sieving as well as ion-specific interactions to achieve remarkable single-channel fluxes and selectivities.…”