LAUSR

Abstract The nanostructural features of polymer inclusion membranes (PIMs) containing one of three polymers, and a variety of carriers and plasticisers, were determined using small- and wide-angle X-ray scattering (SAXS/WAXS). Poly (vinyl chloride) (PVC), cellulose triacetate (CTA) and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) were used as the polymers. Pure polymer membranes were generally found to contain alternating crystalline and amorphous regions of polymer. In all PIMs containing a carrier, the carrier formed repeating nanometre-sized domains which were phase-separated from the polymer; the remaining carrier fraction was localised to the polymer's amorphous phase. Extraction of Yb(III) by membranes containing di (2-ethylhexyl)phosphoric acid showed that only the carrier present in the repeating nano-domains was bound to the metal, and that these nano-domains were therefore continuously linked all the way to the membrane surface. The most likely structure adopted by the carrier was found to be irregular, winding channels of 1–2 nm average diameter. Plasticisers added to PIMs containing a carrier were found to be distributed between the polymer chains and carrier nano-domains just like the carriers themselves, even forming nano-domains of their own. The results suggest that a degree of immiscibility between the polymer and carrier is required for the carrier to phase-separate and form the structures required for chemical extraction.