Asymmetric Solvent-Annealed Triblock Terpolymer Thick Films Topped by a Hexagonal Perforated Lamellar Nanostructure

Abstract : Asymmetric and nanostructured polystyrene-block-poly(2-vinyl pyridine)-block-poly(ethylene oxide) (PS-b-P2VP-b-PEO or SVEO, S:V:EO ≈ 56:34:10, M ∼ 79.5 kg.mol–1 and Đ ∼ 1.05) thick films blended with 20 wt % of a short PS homopolymer (hPS, M ∼ 10.5 kg.mol–1 and Đ ∼ 1.09) were achieved by combining the non-solvent induced phase separation (NIPS) process with a solvent vapor annealing (SVA) treatment. Here, the NIPS step allows for the formation of a highly-permeable sponge-like substructure topped by a dense thin layer exhibiting poorly-ordered nanopores while the subsequent SVA treatment enables to reconstruct the material top surface into a porous monolayer of well-ordered hexagonal perforated lamellae (HPL). This optimized film architecture generated by NIPS-SVA showed a mean water permeability of 860 L h–1 m–2 bar–1, which is roughly twice time higher than the flux measured through NIPS made PS-b-P2VP-b-PEO/hPS materials having poorly-ordered nanopores. The post-SVA treatment also revealed as a powerful tool to tailor the thickness of the nanostructure formed within the blended material since monoliths entirely composed of a HPL phase were produced by increasing the time of exposure to a chloroform stream. The water flux of such PS-b-P2VP-b-PEO/hPS monoliths was found to be an order of magnitude lower than that of their asymmetric film homologues.