Solution self‐assembly behavior of A‐B‐C triblock polymers and the implications for nanoporous membrane fabrication

Self-assembled block polymer membranes are rising to the fore of next-generation separations technologies, and a particular fabrication process of significant interest is the self-assembly and non-solvent induced phase-separation (SNIPS) method. This is because the SNIPS process allows for the facile manipulation of independent variables to produce simultaneously size- and chemically–selective membranes in a scalable manner. Despite significant advances in the SNIPS membrane fabrication procedure, the early-stage solution behavior of many of the polymer–solvent systems employed is still poorly understood. This work addresses the challenges posed by these systems and illuminates guiding relationships for the optimization of SNIPS membrane casting solutions. Specifically, polymer aggregate structures and critical micelle concentration (CMC) values are determined for an A-B-C triblock polymer dissolved in 1,4-dioxane using a combination of scattering and atomic force microscopy techniques. The CMC of this system ranges from 20 to 80 μM and shows a strong dependence on the polymer composition and solution processing method. Additionally, the shape of the self-assembled structures in solution can be altered by varying these parameters. These studies establish the relationships between polymer solution properties (i.e., the block polymer composition and the processing method) and assembly behavior as they impact membrane fabrication through SNIPS processing. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45531.