Nano technological study showing that self-assembled membrane with water-continuous transport pathways for precise nanofiltration; Self-assembled materials are attractive for next-generation materials; but their potential to assemble at the nanoscale and form nanostructures remaining challenging. In the study, they explored size-selective transport in the water-continuous medium of a nanostructured polymer template formed using a self-assembled lyotropic H1 mesophase.
They optimized the mesophase composition to facilitate high-fidelity retention of the H1 structure on photoinduced crosslinking. The membrane contained hexagonally ordered molecular nanofibrils realized by crosslinking a direct cylindrical lyotropic LC. The membrane was mechanically robust and resilient against both dehydration and swelling by excess water.
The self-assembled structure provided uniform and well-defined spacing between nanofibrils for high membrane selectivity and reduced membrane complexity, departing from previously reported work. To form a polymerizable H1 mesophase with water; the research team used a cationic surfactant, 2-ethyl tetradecyl dimethyl ammonium bromide alongside additional crosslinkers of ethylene glycol dimethacrylate and oligo dimethacrylate.
Pathways for precise nanofiltration
The research team synthesizing the surfactant monomer or surfmer in a single-step Menshutkin reaction and formed H1phases at room temperature using METDAB concentrations ranging from 55 to 80 weight percentage. They optimized the composition to develop 70 weight percent METDAB with 22. 8 weight percent water, 5.4 weight percent OEG-DMA and 1.8 weight percent EG-DMA with photoinitiator to form a stable, homogenous H1 mesophase gel.
The resulting gel sample showed excellent transparency to retain integrity after immersing in water for 24 hours for resistance against structural collapse due to water swelling. The water-continuous nature of the self-assembled, cross-linked H1 mesophase and its mechanical resilience was attractive for membrane application, which Feng et al. tested as a proof-of-concept. For this, they produced a membrane by cross-linking a thin film of the H1 mesophase with UV exposure; on a commercially sourced, polyacrylonitrile (PAN) ultrafiltration membrane.
Permeabilities and function
During the experiments, the composite membranes showed strong size selectivity; toward charged organic dye molecules. But based on the transport data, showed that the membrane could effectively separate solutes; on the basis of their size and charge. The permeabilities and function of the self-assembled nanomembranes developed in the study; compared favorably with commercial nanofiltration membranes such as Dow FILMTEC NF90-400.
But using the membrane, they demonstrated clear, size-based selectivity with molecular dyes as model solutes; alongside water permeabilities approximating 10 liters m−2 hour−1 bar−1 μm. But the research team aims to optimize the procedures of fabrication to provide thinner selective layers; but by modifying the surface chemistry of the nanofibrils for water nanofiltration and treatment; using antimicrobial membranes in practical applications.