Poly(N-isopropylacrylamide) grafted into nanopores: Thermo-responsive behaviour in the presence of different salts

Surface initiated polymerization of N(isopropylacrylamide) (NIPAM) was performed by controlled radical polymerization on PET track-etched membranes presenting two different pore diameters (narrow pores: ∼80 nm and large pores: ∼330 nm). The opening and closing characteristics of the resulting PNIPAM-g-PET membranes were investigated by conductometric measurements carried out at different temperatures below and above the LCST of PNIPAM and in the presence of different salts. Depending on the membrane pore size, two types of permeation control mechanisms are observed. In large pore membranes, expanded PNIPAM chains conformations result in reduced effective pore size and therefore lower permeabilities relative to collapsed macromolecules chain conformations. In contrast, in narrow pore membranes, the expanded PNIPAM brush presents greater degrees of hydration in the surface layer and therefore gives rise to higher permeabilities than the collapsed conformation. In this situation, the overall permeability is thus comparable to that of a hydrogel membrane.