(376s) Microscopic Diffusion of Ethylene in ZIF-11 Based Mixed Matrix Membranes (MMMs) By Pulsed Field Gradient (PFG) NMR

Mixed matrix membranes (MMMs) have attracted attention of the scientific community due to their easy and scalable fabrication, as well as superior gas separation performance compared to pure polymeric membranes. MMMs are formed by dispersing permeable filler particles in a polymer matrix. Recently, zeolitic imidazole frameworks (ZIFs) have been considered for filler particles due to their great thermal and chemical stability, high surface area and tunable frameworks which have made them more compatible with polymers compared to other types of filler particles.

Detailed understanding of molecular diffusion inside ZIF particles dispersed in MMMs is important for their potential applications in gas separations. Here we report microscopic studies of diffusion of ethylene inside different ZIF-11-based MMMs at equivalent loading pressures. Diffusion measurements were performed using ¹³C pulsed field gradient (PFG) NMR utilizing a high field (17.6 T) and high magnetic field gradients (up to 25 T/m) to obtain diffusivities for the length scales of displacements smaller than the mean size of the ZIF-11 crystals. It was found that the diffusivity of ethylene inside ZIF-11 particles for displacements much smaller than the particle size is influenced by the particle confinement in the polymer. This observation is attributed to the ability of the polymer to restrict framework flexibility of the dispersed ZIF-11 particles in the polymer.