Highly Selective and Tunable CO₂/N₂ Separation Performance in Ammonium-Based Organic Ionic Plastic Crystal Composite Membranes with Self-Healing Properties

An advancement in light gas separation performance is realized by using organic ionic plastic crystal (OIPC)-based composites. In this work, a composite membrane is synthesized from tetraethylammonium bis(fluorosulfonyl)imide ([N2222][FSI]) and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) for the first time and tested under different thermal conditions to investigate the performance in different solid phases. The composite demonstrates tunable performance within a small range of temperatures and enhanced CO2 solubility upon annealing, reaching a CO2 permeability of ∼130 barrer with a remarkable CO2/N2 selectivity of α ≈ 70 at 55 °C. The thermophysical properties of the composite reveal a strong dependency between the structure and the overall gas separation performance. Higher homogeneity in the [N2222][FSI]:PVDF-HFP mixture is concluded to hinder OIPC crystallinity and enhance interfacial disorder, boosting CO2 solubility and ionic conductivity and concomitantly providing good mechanical support. Additionally, self-healing behavior is observed in the composite, which makes it more attractive for practical applications. These results provide valuable insights into the advanced design of more selective and durable OIPC-based composite membranes for light gas separation.