(562d) Ultrathin and Pinhole-Free Gas-Selective Polymeric Films Synthesized Via Chemical Vapor Deposition

Gas separation has gained enormous interest due to the increasing industrial demand for pure gas species and the urgency for carbon capture. Among various gas separation techniques, polymer membrane based separation process is considered to be an energy-efficient alternative for conventional cryogenic distillation and sorbents based separation. In order to simultaneously achieve high flux and high selectivity, a typical membrane has an anisotropic structure consisting of an ultra-permeable support and an ultrathin gas-selective skin layer, since the flux is inversely proportional to the skin layer thickness. However, avoiding the pinhole formation in sub-100 nm membranes has proven to be difficult for solution based fabrication techniques, such as phase inversion. In this regard, we introduced chemical vapor deposition (CVD) as a powerful technique to synthesize ultrathin and pinhole-free gas-selective polymeric films. CVD was chosen for several reasons: 1) depositing pinhole-free films with precise thickness control at nanometer level; 2) large library of starting monomers; 3) substrate independency; 4) in situ covalent crosslinkability; and 5) scalability. In this talk, sub-100 nm pinhole-free gas-selective membranes as large as 175 cm² were successfully deposited on top of ultrapermeable poly[1-(trimethylsilyl)-propyne] (PTMSP) cast membranes. The large library of starting monomers has allowed us to fine tune the polymer structure to meet different gas separation purposes. For instance, the robust porphyrin derived sub-100 nm microporous films led to high CO₂/N₂ selectivity (ca. 85) and a negligible H₂/CO₂ selectivity (< 2). In contrast, an ionic monomer acrylic acid (AA) derived sub-10 nm membrane displayed a significant H₂/CO₂ selectivity (ca. 45) but a moderate CO₂/N₂ selectivity (ca. 15). Such CVD synthesized gas-selective films were also successfully cross-linked by employing a vaporized cross-linker to enhance the film durability. Future work will focus on designing new gas-selective CVD polymers and exploring new substrate options that are less prone to physical aging. The work reported in this talk should provide insight to the membrane community on the possibility of employing CVD to fabricate gas-selective polymeric films.