(822c) Developing Tunable Ultrafiltration Membranes With Chemically-Tailored Pore Walls From Triblock Terpolymer Templates
Recent reports suggest that self-assembled block copolymers are an excellent platform for producing next-generation ultrafiltration (UF) membranes. Because the self-assembly of the block copolymer results in a high density of singly-sized pores, whose diameter can be tuned via the copolymer synthesis, these membranes have the potential to provide superior performance when compared to current membranes. However, the copolymer membranes produced thus far contain pore walls that are lined by a limited number of chemical functionalities, whereas tailored pore chemistries are preferred. This collaborative work addresses this shortcoming in order to produce UF membranes that can be chemically tailored, in a facile and scalable manner, to the specific needs of a multitude of applications.
Here we will discuss efforts to make large membrane areas from a poly(isoprene-b-styrene-b-N,N-dimethylacrylamide) (PI-PS-PDMA) triblock terpolymer using the self-assembly and non-solvent induced phase separation (SNIPS) method. Using a simple process after membrane fabrication, the PDMA groups that line the pore walls are converted to polyacrylic acid (PAA), which can be reacted further to functionalize the membrane pores. A suite of x-ray scattering and advanced microscopy characterization techniques (SAXS, SEM, AFM) are used to explore systematically the nanostructure of the terpolymer membrane at each step of the process (i.e., during the fabrication of the parent membrane, the deprotection step, and the subsequent pore wall functionalization). These characterization techniques show that the SNIPS process produces an asymmetric membrane with a thin active layer, which contains 1.85 × 1013 self-assembled pores per m2 of membrane with diameters that can range from 5-10 nm, on top of a microporous support. The membrane maintains its nanoporous structure following the deprotection and functionalization steps. Transport tests also are conducted at each stage to quantify the hydraulic permeability and solute rejection capabilities of the membrane. This combination of material characterization and transport testing lays the groundwork for the development of structure-property-performance relationships that can guide the use of these versatile block terpolymer membranes in filtration, sensing, and drug delivery applications.