(498e) Influence of Polymer Crosslinking on Microscopic Diffusion of Liquids in MOF-Based Mixed Matrix Membranes

For liquid separations, crosslinked polymers are desirable in mixed-matrix membranes (MMMs), which are formed by dispersing crystals of metal–organic frameworks (MOFs) in polymers. A crosslinking process can reduce polymer dilation and plasticization effects by liquid sorbates. However, polymer crosslinking can unfavorably change transport and related structural properties of MOF fillers. In this work, C-13 pulsed field gradient (PFG) NMR was used to investigate changes in intra-MOF self-diffusion of p-xylene and o-xylene after MMM polymer crosslinking. The reported PFG NMR data indicate that the polymer crosslinking process used does not influence the intra-ZIF diffusivities when all effects on these diffusivities that are related to diffusing molecules crossing over the crystal boundaries or reflected away from these boundaries are removed. However, these data also show that the crosslinking process resulted in a disruption of external surface layers of MOF crystals. Such surface layer disruption is equivalent to a decrease in the effective sizes of ZIF crystals when their transport properties are quantified. This conclusion was found to be in agreement with the results of electron microscopy analysis. PFG NMR studies and data analysis similar to those presented in this work can be used for quantifying any types of MOF crystal degradation inside MOF-based MMMs.