(728b) Understanding the Formation Pathways of Triblock Terpolymer Membranes

Block copolymer-directed self-assembly has enabled the synthesis of porous, nanostructured functional materials with high specific surface areas, tunable morphologies, and periodic nanopores. Increasing pore accessibility, a critical factor in membrane and electrode performance, has been achieved through nonsolvent-induced phase separation (SNIPS), which relies on the partial evaporation of a BCP solution to form a thin, ordered liquid crystalline micelle layer above a low order, asymmetric under-layer. By plunging this graded gel into a nonsolvent bath, the structure is frozen into the solid polymer, an ordered mesoporous surface layer supported by a graded, asymmetric macroporous substructure.

 Recently, we have shown that the SNIPS process can be combined with BCP-directed co-assembly of phenol-formaldehyde resols to produce tunable, graded, hierarchically porous carbon material [1]. However, the formation mechanisms of SNIPS derived membranes, even without the complicating inclusions of inorganic additives, are not fully agreed upon. Understanding the solution micelle formation and structure evolution has the potential to significantly advance the ability of the community to target specific pore sizes, expand the variety of functional materials accessible via this approach, and produce better-ordered structures with improved reliability.

 Our work in high-resolution ultrafiltration membranes and BCP-derived functional graded materials has focused on the asymmetric triblock terpolymer, polyisoprene-block-polystyrene-block-poly(4-vinyl pyridine), which can yield cubically packed pores. Via a combination of ex-situ and in-situ scattering measurements, we have examined the micellar solutions and their transformation from disordered to ordered structures in order to understand the varied morphologies produced by triblock derived membranes and the alterations induced by additive incorporation.

 [1] S.A. Hesse, J.G. Werner, U. Wiesner ACS Macro Lett. 4, 477-482 (2015).