Microscopic mechanism of gas transport in mixed matrix membranes of coordination nanocages

• Published in: Journal of membrane science 2023-10, Vol.683, p.121821, Article 121821
• Main Authors: Liu, Yuan, Xue, Binghui, Lai, Yuyan, Cai, Linkun, Chen, Kun, Yin, Panchao
• Format: Article
• Language: English
• Subjects: Coordination nanocages; Gas separation membranes; Mixed-matrix membranes; Polymer dynamics; Polymer nanocomposites
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/j.memsci.2023.121821

The strong inter-phase attraction is required for the effective and stable integration of inorganics and polymers in mixed matrix membranes (MMMs), which would impact the structures and microscopic dynamics of the two phases and cause unexpected deviation of MMM performance from original design; however, the understanding of its structure-property relationship is still poor. Herein, 2 nm coordination nanocage (CNC) with well-defined, monodispersed structure is complexed with poly(4-vinyl pyridine-r-n-butyl acrylate) (P4VP-co-PnBA) via both coordination and hydrogen bonding to afford model systems. The surface interaction between the two phases is quantified by the thickness of absorbed layers of polymers on CNC surface as well as the segmental dynamics of polymers. In broadband dielectric spectroscopy (BDS) studies, accelerated chain dynamics can be observed in the nanocomposites with loadings of CNC, which is originated from the frustrated packing of polymers absorbed on CNC surface. The co-effect of interfacial layer thickness and chain dynamics leads to the non-monotonic dependence of the MMMs’ gas permeabilities on CNC concentrations. The temperature dependence of their gas permeability and chain dynamics are both explored and the two processes are fully decoupled at temperatures higher than 333 K due to the weakening of multiple supramolecular interaction. Our discoveries provide microscopic and quantitative understanding on structure-property relationship of MMMs, which benefits directly to the rational design of polymer structures for optimized gas separation performance. [Display omitted] •Quantified structure-property relationship of mixed matrix membranes is provided.•The dynamics of polymer are probed for understanding the inter-phase interaction.•The information of interfacial polymer layers on nano-filler surface are revealed.•The nonmonotonic dependence of gas permeabilities on filler loadings is deciphered.