C60-polysulfone nanocomposite membranes: Entropic and enthalpic determinants of C60 aggregation and its effects on membrane properties

The study focuses on the effects of C60 filler on the phase inversion process and related changes in the morphology and separation properties of cast C60-polysulfone nanocomposite membranes. The effects of C60 on the rejection and permeability of the cast membranes are correlated to rheological and demixing properties of the corresponding casting mixtures. The observed differences between C60-free and nanocomposite membranes are interpreted as resulting from enthalpic and entropic C60-polysulfone interactions that drive and are mediated by the aggregation of C60. Only 30 nm and smaller C60 aggregates are observed in membranes with the smallest (1% C60/polysulfone by mass) C60 loading. In contrast, only aggregates larger than 30 nm are found in composites with 5% and 10% C60 loadings. A correlation between the demixing rate and permeability and a counter-correlation between permeability and rejection are observed for nanocomposite membranes for the entire C60 loadings range studied. The observed accumulation of the filler at the surface of internal membrane pores is attributed to the expulsion of C60 aggregates to the free surface for an entropic gain. The findings have implications for the design of polymer nanocomposite membranes as well as for the lifecycle analysis of nanomaterial-enabled products.