Nanoscale Thickness Control of Nanoporous Films Derived from Directionally Photopolymerized Mesophases

• Published in: Advanced materials interfaces Vol. 8; no. 5
• Main Authors: Imran, Omar Q., Kim, Na Kyung, Bodkin, Lauren N., Dwulet, Gregory E., Feng, Xunda, Kawabata, Kohsuke, Elimelech, Menachem, Gin, Douglas L., Osuji, Chinedum O.
• Format: Journal Article
• Language: English
• Published: Weinheim John Wiley & Sons, Inc 01.03.2021
• Subjects: Attenuation; Bleaching; Film growth; Film thickness; frontal photopolymerization; Functional materials; Mathematical models; Membranes; Mesophase; Nanofiltration; nanoporous films; Nanostructure; Nanostructured materials; Permeability; Photopolymerization; Reverse osmosis; templated mesophase; thickness control; Thin films
• DOI: 10.1002/admi.202001977
• ISSN: 2196-7350

The preparation of thin films of nanostructured functional materials is a critical step in a diverse array of applications ranging from photonics to separation science. New thin‐film fabrication methods are sought to harness the emerging potential of self‐assembled nanostructured materials as next‐generation membranes. Here, the authors show that nanometer‐scale control over the thickness of self‐assembled mesophases can be enacted by directional photopolymerization in the presence of highly photo‐attenuating molecular species. Metrology reveals average film growth rates below ten nanometers per second, indicating that high‐resolution fabrication is possible with this approach. The trends in experimental data are reproduced well in numerical simulations of mean‐field frontal photopolymerization modeled in a highly photo‐attenuating and photo‐bleaching medium. These simulation results connect the experimentally observed nanometer‐scale control of film growth to the strong photo‐attenuating nature of the mesophase, which originates from its high‐aromatic‐ring content. Water permeability measurements conducted on the fabricated thin films show the expected linear scaling of permeability with film thickness. Film permeabilities compare favorably with current state‐of‐the‐art nanofiltration and reverse osmosis membranes, suggesting that the current approach may be utilized to prepare new nanoporous membranes for such applications. Frontal photopolymerization is introduced as an alternative to spin‐coating for directionally growing cross‐linked films of discotic supramolecular assemblies at unprecedented high‐resolution growth rates of ≈5 nm s−1. Proof‐of‐concept of this technique is provided by the fabrication of sub‐micrometer thin‐film nanoporous membranes which exhibit an expected water permeability scaling with film thickness.