Cyclodextrin-based supramolecular polymeric nanoparticles for next generation gas separation membranes†
Cyclodextrin-based supramolecular assemblies derived from poly(dimethylsiloxane) (PDMS) functionalized polyrotaxanes (PRXs) were self-assembled into core–shell morphologies and used as soft nanoparticle (SNP) additives in the selective layer of thin film composite (TFC) membranes for the first time. Various weight percentages (wt%) of the PRX SNP additives were combined with Pebax® 2533 to form the selective layer, and the gas transport properties of the TFC membranes were studied in detail. Increasing the amount of PRX SNP additives led to a significant increase in CO2 permeance of the membranes, with only a slight decrease in the CO2/N2 selectivity, which was attributed to the dynamic nature (i.e., translational and rotational freedom) of the conjugated PDMS chains on the PRXs. In comparison, the performance of membranes prepared using a conventional analogue with fixed PDMS chains was inferior. The excellent gas transport properties observed for membranes are attributed to the novel self-assembly process of the dynamic PRX SNP additives; the sliding nature of the conjugated PDMS chains allow for increased exposure of the CO2-philic PEG backbone and increased size of the hydrophobic core leading to improved membrane selectivity and permeability. The effect of varying operating conditions (feed pressure and temperature) was also investigated and compared between the dynamic and fixed additive systems. Interesting trends were observed with the dynamic PRX system which diverges from conventional systems. This study opens up new avenues for CD-based supramolecular chemistry in the field of membrane technologies for gas separation.