Tuning Interfacial Interactions for One-step Ordering of Block Copolymer Films with Tunable Pore Sizes for Wastewater Filtration Membranes*

Wastewater is now contaminated with oil, organic compounds, toxic metals, and a variety of complex impurities due to the rapid rise in oil and gas, petrochemical, pharmaceutical, and food processing industries. Polymeric membranes present an easy and energy-efficient solution for wastewater filtration. Versatile membranes that remove both particulate and oily matter from wastewater using multiple separation mechanisms are highly desirable. This work presents a methodology to rapidly order block copolymer thin films with well-defined through-thickness channels having minimal tortuosity. The technique involves casting BCP films from solution mixtures doped with block-selective plasticizing additives that segregate into one of the BCP domains. Owing to the selectivity and plasticization capability of the additive, its preferential solvation of BCP components in the solvent mixture, and its interaction with the substrate, the film is fully ordered with perpendicular domains on unmodified substrates. With careful selection of the casting environment, i.e., the concentration of the additive and the selective solvents, completely perpendicular domain morphologies with tunable domain sizes can be achieved during the casting process, potentially giving high fluxes and variable pore sizes. The thin BCP films form the active layers and are supported by commercial membranes like polyether sulfone for mechanical strength. They are treated to selectively crosslink one and etch the other block to open the pores which have size cutoffs for 90 percent solute rejection in the range of 40 nm to 80 nm. With monodisperse pore sizes and low tortuosity, they overcome the limitations of size segregation and flux. The perpendicular assembly is characterized by using atomic force microscopy and grazing incidence small angle x-ray scattering. At the same time, membrane performance is tested using a dead-end pressure cell to study flux, membrane stability, and separation efficiency for polymer solutions and oil/water suspensions.