Process-Directed Self-Assembly of Copolymer Blends: II. Continuous Tuning of Structure Size

Combining self-consistent field theory and single-chain-in-mean-field simulations, we study the self-assembled morphology and structure size of binary diblock copolymer blends in equilibrium and after processingsuch as quenching, annealing, evaporation-induced self-assembly (EISA), and nonsolvent-induced phase separation (NIPS). The equilibrium phase diagrams reveal that adding long linear A(2)B(2) copolymers to a melt of shorter, cylinder-forming linear A(1)B(1) copolymers can enlarge the equilibrium cylinder radius by at least 3-fold before macrophase separation sets in. Our particle-based simulations uncover a strong dependence of structure size on processing pathways. Notably, blending A(2)B(2) copolymers results in a higher magnification of cylinder radii in EISA compared to quenching or annealing. We further analyze how this blending strategy tailors the pore size and transforms the morphological characteristics of integral asymmetric isoporous membranes fabricated by NIPS. By blending in a second diblock copolymer that is 2.25 times the length of the host, a pore-size magnification of up to 70% can be achieved. With further optimization, a more than 2-fold increase appears attainable without significantly compromising membrane quality. Overall, our study offers insights into the structure-processing-property relationships in block copolymer systems and provides design principles for tailoring nanostructures through blend composition and processing strategies across a range of applications.