Self-assembled materials are attractive for next-generation membranes. However, the need to align self-assembled nanostructures (e.g. cylinders, lamellae) and the narrow stability windows for ordered bicontinuous systems present serious challenges. We propose and demonstrate a novel approach that circumvents these challenges by exploiting size-selective transport in the water-continuous medium of a nanostructured polymer templated from a self-assembled lyotropic H1 mesophase. Optimization of the mesophase composition enables high-fidelity retention of the H1 structure on photoinduced cross-linking. The resulting material is a mechanically robust nanostructured polymer possessing internally and externally cross-linked nanofibrils surrounded by a continuous aqueous medium. Fabricated membranes show size selectivity at the 1- to 2-nm length scale and water permeabilities of ~10 liters m−2 hour−1 bar−1 μm. Moreover, the membranes display excellent antimicrobial properties due to the quaternary ammonium groups on the nanofibril surfaces. These results represent a breakthrough for the potential use of polymerized lyotropic mesophase membranes in practical water purification applications.

Increased demand for highly selective and energy-efficient separations processes has stimulated substantial interest in emerging two-dimensional (2D) nanomaterials as a potential platform for next-generation membranes. However, persistently poor separation performance continues to hinder the viability of many novel 2D-nanosheet membranes in desalination applications. In this study, we examine the role of the lamellar structure of 2D membranes on their performance. Using self-fabricated molybdenum disulfide (MoS2) membranes as a platform, we show that the separation layer of 2D nanosheet frameworks not only fails to demonstrate water-salt selectivity but also exhibits low rejection toward dye molecules. Moreover, the MoS2 membranes possess a molecular weight cutoff comparable to its underlying porous support, implying negligible selectivity of the MoS2 layer. By tuning the nanochannel size through intercalation with amphiphilic molecules and analyzing mass transport in the lamellar structure using Monte Carlo simulations, we reveal that small imperfections in the stacking of MoS2 nanosheets result in the formation of catastrophic microporous defects. These defects lead to a precipitous reduction in the selectivity of the lamellar structure by negating the interlayer sieving mechanism that prevents the passage of large penetrants. Notably, the imperfect stacking of nanosheets in the MoS2 membrane was further verified using 2D X-ray diffraction measurements. We conclude that developing a well-controlled fabrication process, in which the lamellar structure can be carefully tuned, is critical to achieving defect-free and highly selective 2D desalination membranes.

The interaction of two-dimensional (2D) nanomaterials with biological membranes has important implications for ecotoxicity and human health. In this study, we use a dye-leakage assay to quantitatively assess the disruption of a model phospholipid bilayer membrane (i.e., lipid vesicles) by five emerging 2D nanomaterials: graphene oxide (GO), reduced graphene oxide (rGO), molybdenum disulfide (MoS2), copper oxide (CuO), and iron oxide (α-Fe2O3). Leakage of dye from the vesicle inner solution, which indicates loss of membrane integrity, was observed for GO, rGO, and MoS2 nanosheets but not for CuO and α-Fe2O3, implying that 2D morphology by itself is not sufficient to cause loss of membrane integrity. Mixing GO and rGO with lipid vesicles induced aggregation, whereas enhanced stability (dispersion) was observed with MoS2 nanosheets, suggesting different aggregation mechanisms for the 2D nanomaterials upon interaction with lipid bilayers. No loss of membrane integrity was observed under strong oxidative conditions, indicating that nanosheet-driven membrane disruption stemmed from a physical mechanism rather than chemical oxidation. For GO, the most disruptive nanomaterial, we show that the extent of membrane integrity loss was dependent on total surface area, not edge length, which is consistent with a lipid-extraction mechanism and inconsistent with a piercing mechanism.

Nanostructured materials with precisely defined and water-bicontinuous 1-nm-scale pores are highly sought after as advanced materials for next-generation nanofiltration membranes. While several self-assembled systems appear to satisfy this need, straightforward fabrication of such materials as submicron films with high-fidelity retention of their ordered nanostructure represents a nontrivial challenge. We report the development of a lyotropic liquid crystal mesophase that addresses the aforementioned issue. Films as thin as ∼200 nm are prepared on conventional support membranes using solution-based methods. Within these films, the system is composed of a hexagonally ordered array of ∼3 nm diameter cylinders of cross-linked polymer, embedded in an aqueous medium. The cylinders are uniformly oriented in the plane of the film, providing a transport-limiting dimension of ∼1 nm, associated with the space between the outer surfaces of nearest-neighbor cylinders. These membranes exhibit molecular weight cutoffs of ∼300 Da for organic solutes and are effective in rejecting dissolved salts, and in particular, divalent species, while exhibiting water permeabilities that rival or exceed current state-of-the-art commercial nanofiltration membranes. These materials have the ability to address a broad range of nanofiltration applications, while structure–property considerations suggest several avenues for potential performance improvements.

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Atomically thin MoS 2 nanosheets are of interest due to unique electronic, optical, and catalytic properties that are absent in the bulk material. Methods to prepare nanosheets from bulk material that facilitate studies of 2D-MoS 2 and the fabrication of useful devices have consequently assumed considerable importance. Here, we report the simultaneous exfoliation and stable dispersion of MoS 2 nanosheets in a liquid crystal. Exfoliation of bulk MoS 2 in mesogen-containing solutions produced stable dispersions of 2D-MoS 2 that retained suspension stability for several weeks. Solvent removal in cast films yielded nanocomposites of 2D-MoS 2 . Preservation of single-and few-sheet MoS 2 was confirmed utilizing UV−vis and Raman spectroscopy in the nematic and isotropic fluid states of the system and, remarkably, in the solid crystal as well. Importantly, the MoS 2 nanosheets remained welldispersed upon polymerization of the reactive mesogen to form a liquid crystal polymer. The ability to stably disperse 2D-MoS 2 in a structured fluid opens up new possibilities for studying anisotropic properties of MoS 2 and for exploiting such properties in responsive materials.

The self-assembly of liquid crystals (LCs) in small volumes is mediated by the anchoring conditions of the constituent mesogens at the confining surfaces. In hierarchically ordered systems such as LC block copolymers, the importance of anchoring at external as well as internal interfaces can give rise to intriguing phenomena. Here, we examine the morphology of thin films of liquid crystalline block copolymers (LC BCPs) in the presence of non-bonded, or labile, mesogens and explore the manner in which external anchoring conditions of the LC control the orientation of the block copolymer superstructure. We find that the addition of 4′-(hexyloxy)-4-biphenylcarbonitrile (6OCB) mesogens induces an orientation change of cylinder- or lamellae-forming LC BCPs, from parallel to perpendicular with respect to the film surface. Systematic variations of free mesogen concentration, thermal annealing conditions, film thickness, and the type of free mesogens added were conducted. Our results indicate that labile 6OCB mesogens co-assemble with their backbone-bonded counterparts and adopt homeotropic anchoring at the free surface (air interface). Coupled with homogeneous anchoring of the LC mesophase at the internal block copolymer interface, the labile mesogens induce a perpendicular orientation of the BCP superstructure in thin films. We exploit this behavior as a mechanism to control BCP morphology and demonstrate the formation of perpendicular structures on topographically patterned substrates. Investigations conducted with different mesogens point to the importance of the labile mesogen anchoring at the air interface and steric constraints on co-assembly with backbone-bonded mesogens as key aspects dictating the ability of labile mesogens to control the BCP morphology in thin films. On this basis, we discuss design rules for mesogenic additives that can be used to engineer LC BCP morphology in thin films.

Realizing metamaterials with desired plasmonic properties requires the fabrication of nanomaterial arrays with tailored geometries, viz., controlled nanomaterial size, orientation, and spacing. Here, a novel approach for creating arrays of vertically oriented plasmonic nanorods (NRs) using templates formed by macromolecular self-assembly is examined, and results regarding the optical properties of such arrays are presented. ZnO NRs are synthesized hydrothermally using block copolymer templates, where the size and spacing of NRs are predetermined with high fidelity by the self-assembled template. The NRs are thereafter used as scaffolds for the production of a Au shell, giving rise to distinct plasmonic hotspots, as shown in finite-difference time-domain (FDTD) simulations. Correspondingly, surface-enhanced Raman scattering (SERS) measurements demonstrate the detection of small organic analytes at concentrations as low as 50 nM. These results demonstrate the utility of such arrays as SERS sensors and highlight their potential for sensing based on guided SPR modes, with considerable enhancement of sensitivity. The ability to rapidly fabricate these ordered Au-shell NR arrays under ambient conditions represents an additionally compelling aspect.