Nanoscale Thickness Control of Nanoporous Films Derived from Directionally Photopolymerized Mesophases

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.