(605f) Anomalous Structural Transitions and Gas Transport Properties in Ultrathin Films of Polymers of Intrinsic Microporosity

Solution-processable polymers of intrinsic microporosity (PIMs) have been explored as a next-generation material for gas separation membranes by featuring abundant micropores (<2 nm) for fast and selective gas transport. To date, significant efforts have been devoted to designing novel and high-performance PIMs in the form of bulk films (>50 µm). However, little attention has been paid to membrane engineering – converting the developed PIM materials into thin membranes to maximize the gas permeance for real-world applications. Herein, we highlight the critical need for understanding the transition from bulk PIM materials to their thin films (<1 µm). 6FDA-DAM and PIM-1 were chosen as archetypal PIMs and their thin-film composite (TFC) membranes were prepared via a spin-coating method. The TFC membranes always exhibited a lower gas permeability compared to the model prediction based on bulk-film-based data. Moreover, such deviations became more pronounced as reducing the selective layer thickness down to several tens of nanometers. Two-dimensional grazing-incidence wide-angle X-ray scattering (2D GIWAXS) analyses reveal that PIM thin films significantly differ from those of bulk films by showing thickness-dependent anisotropic microstructures potentially due to confinement effects. To overcome this issue, we propose exploiting beneficial aging effects in PIM thin films to boost their gas selectivities.