Interfacial crosslinking to prepare ultra-thin polydimethylsiloxane thin-film composite membranes

Thin film composite (TFC) membranes have emerged as pivotal components in diverse industrial applications, including carbon capture, water purification, and gas separation. Among membrane materials, polydimethylsiloxane (PDMS) stands out for its high gas permeability, making it ideal as a selective layer for some industrial separations and as a gutter or protective layer for other membranes. This study focuses on the development of ultra-thin PDMS-based TFC membranes in a process mirroring interfacial polymerization, aiming to achieve defect-free films with enhanced gas permeance and selectivity. By varying acid-chloride-functionalized PDMS and polyethylenimine (PEI) concentrations in the organic and aqueous phases, respectively, and optimizing reaction times, membranes were fabricated and characterized for their morphological, chemical, and performance properties. Results demonstrate that the interfacial crosslinking approach can produce defect-free PDMS films as thin as ∼50 nm, significantly thinner than conventional PDMS TFC membranes produced through coating methods. Gas permeation tests revealed high CO 2 permeance and selectivity (e.g., 3290 ± 340 GPU with a CO 2 /N 2 selectivity of 12 ± 3), showcasing potential for efficient gas separation applications. Furthermore, this technique of using polymers with reactive end groups in interfacial crosslinking to yield ultra-thin rubbery selective layers may prove useful for a variety of different polymer chemistries and membrane applications. • Interfacial polymerization was extended to make ultra-thin (∼50 nm) and defect-free PDMS selective layers. • Acid-chloride-terminated PDMS in the organic phase was crosslinked using polyethyleneimine (PEI) in the aqueous phase. • Maximizing PDMS content, while minimizing PEI content, enhanced CO 2 permeance. • Increased reaction time increased thickness, with decreasing CO 2 permeance and constant CO 2 permeability.