Self-Sorting of Interfacial Compatibility in MOF-Based Mixed Matrix Membranes

Metal-organic framework (MOF)-based mixed matrix membranes (MMMs) have shown great promises to overcome the performance upper limit of polymeric membranes for various gas separation processes. However, the gas separation properties of the MMMs largely depend on the MOF-polymer interfacial compatibility which is a metric difficult to quantify. In most cases, whether a MOF filler and a polymer matrix make a good pair is not revealed until the gas transport experiments are performed. This is because there is a lack of characterization techniques to directly probe the MOF-polymer interfacial compatibility. In this work, we demonstrate a self-sorting method to rank the interface compatibility among several MOF-polymer pairs. By mixing one MOF with two polymers in an MMM, the demixing of two polymers will form two polymer domains. The MOF particles will preferably partition into the "preferred" polymer domain due to their higher interfacial affinity. By scanning different polymer pairs, a rank of MOF-polymer interfacial compatibility from high to low can be obtained. Moreover, based on this ranking, it was also found that a highly compatible MOF-polymer pair suggested by this method also corresponds to a more predictable MMM gas separation performance.