Mesophase-Derived Polymer Membranes with Precisely Defined Pores for Molecular and Ion Separations

Polymer membranes are central components in critical technologies, including energy generation and storage, water purification, and chemical separations. There are pressing needs for membranes that transport uncharged and charged molecular, or ionic species, with bespoke selectivity and high permeability in these technological areas, including the growing need for efficient critical mineral separations and resource recovery. For these and other challenging molecular or ionic separations, the focus is on membranes with 1 nm scale (0.5–2 nm) pores that can offer both size- and affinity-based mechanisms for separation. This perspective discusses the current state of the art in nanoporous polymer membranes and reviews recent progress toward the realization of ideal membranes for such separations—i.e., membranes with uniform, continuous, and precisely defined pores at the 1 nm length scale. Emphasis is placed on materials derived from molecular self-assembly, particularly lyotropic mesophases formed from amphiphilic monomers that can be crosslinked to produce monolithic membranes with well-defined, continuous transport pathways. These materials represent a potentially important advance given their attractive separation performance, and the versatility with which their properties can be modified. Developments in fabrication, pore shape, and pore chemistry control are discussed, along with opportunities to address important contemporary and emerging applications.