There is long-standing interest in developing membranes possessing uniform pores with dimensions in the range of 1 nm and physical continuity in the macroscopic transport direction to meet the needs of challenging small molecule and ionic separations. Here we report facile, scalabe fabrication of polymer membranes with vertically (i.e., along the through-plane direction) aligned 1 nm pores by magnetic-field alignment and subsequent cross-linking of a liquid crystalline mesophase. We utilize a wedge-shaped amphiphilic species as the building block of a thermotropic columnar mesophase with 1 nm ionic nanochannels, and leverage the magnetic anisotropy of the amphiphile to control the alignment of these pores with a magnetic field. In situ X-ray scattering and subsequent optical microscopy reveal the formation of highly ordered nanostructured mesophases and cross-linked polymer films with orientational order parameters of ca. 0.95. High-resolution transmission electron microscopy (TEM) imaging provides direct visualization of long-range persistence of vertically aligned, hexagonally packed nanopores in unprecedented detail, demonstrating high-fidelity retention of structure and alignment after photo-cross-linking. Ionic conductivity measurements on the aligned membranes show a remarkable 85-fold enhancement of conductivity over nonaligned samples. These results provide a path to achieving the large area control of morphology and related enhancement of properties required for high-performance membranes and other applications.

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Membrane separations are critically important in areas ranging from health care and analytical chemistry to bioprocessing and water purification. An ideal nanoporous membrane would consist of a thin film with physically continuous and vertically aligned nanopores and would display a narrow distribution of pore sizes. However, the current state of the art departs considerably from this ideal and is beset by intrinsic trade-offs between permeability and selectivity. We demonstrate an effective and scalable method to fabricate polymer films with ideal membrane morphologies consisting of submicron thickness films with physically continuous and vertically aligned 1 nm pores. The approach is based on soft confinement to control the orientation of a cross-linkable mesophase in which the pores are produced by self-assembly. The scalability, exceptional ease of fabrication, and potential to create a new class of nanofiltration membranes stand out as compelling aspects.

The bicontinuous cubic (Q) lyotropic liquid crystal (LLC) phases formed by the phase-separation and self-organization of amphiphilic molecules in water are intriguing structures for a number of transport-related applications because they possess ordered, uniform, 3D-interconnected water channels on the size of single molecules. Polymeric materials formed from either the templated polymerization or cross-linking of conventional monomers around Q phases, or the direct polymerization or cross-linking of Q phases formed by reactive amphiphiles retain the desired LLC nanostructure but are more robust for true application development. The structures of Q LLC phases were only elucidated in the late 1980s, and the first successful preparation of polymers based on Q phases was reported soon after. However, the development and demonstration of these nanoporous polymers for material applications were not realized until the first decade of the twenty-first century. This focus review provides an overview of work in the area of Q LLC phase-based polymer materials, with a focus on the work of our research group and that of our collaborators on polymer networks prepared by the direct polymerization of reactive Q phases and their development as functional materials for several engineering applications. Keywords: bicontinuous cubic; liquid crystal; lyotropic; nanoporous; polymer INTRODUCTION Lyotropic liquid crystals (LLCs) are amphiphilic molecules typically composed of a hydrophilic headgroup section and a hydrophobic tail section that have the ability to phase-separate and self-organize into nanostructured assemblies in the presence of water. The resulting fluid, ordered LLC phases have varying degrees of average order, different levels of hydrophilic and hydrophobic domain interconnectivity, and uniform periodic features in the circa 1-10 nm size range (For general reviews on LLC phases and their classifications, see: refs 1-3). LLC phases have recently attracted a great deal of attention because of their benefits as a versatile platform for the design of functional, nanoporous polymer materials. For example, by employing reactive LLCs (that is, monomers), the desired phase can be locked-in directly via chemical cross-linking to afford robust, nanoporous polymer networks (For reviews on the synthesis and applications of nanostructured polymers made from polymerizable LLCs, see: refs 4-6). LLC networks made by this approach have been used for applications such as templated nanocomposite synthesis, drug delivery, molecular transport/separation and heterogeneous catalysis. 7,8 Alternatively, non-polymerizable LLC phases have been used as nanostructured templates for the polymerization of conventional monomers dissolved in either the hydrophilic or hydrophobic domains. Subsequent