Interfacial Engineering of Block Copolymer Nanostructures: Morphology and Solvent Stability

Interfacial engineering is a critical pathway for modulating the self-assembled nanostructures of block copolymers (BCPs) during solvent exchange. Herein, we demonstrated the generation of different stacked lamellae of polystyrene-block-poly(2-vinyl pyridine) (PS-b-P2VP) nanostructures during solvent exchange by using phosphotungstic acid (PTA) or PTA/NaCl aqueous solution as the nonsolvent. The participation of PTA in the confined microphase separation of PS-b-P2VP in droplets increases the volume fraction of P2VP and decreases the tension at the oil/water interface. Moreover, the addition of NaCl to the PTA solution can further increase the surface coverage of P2VP/PTA on droplets. All factors impact the morphology of assembled BCP nanostructures. In the presence of PTA, ellipsoidal particles composed of alternatively stacked lamellae of PS and P2VP were formed (named BP), whereas, in the coexistence of PTA and NaCl, they changed to stacked disks with PS-core-P2VP-shell (called BPN). The different structures of assembled particles induce their different stabilities in solvents and different dissociation conditions as well. The dissociation of BP particles was easy because PS chains were only entangled together which can be swollen in toluene or chloroform. However, the dissociation of BPN was hard, requiring an organic base in hot ethanol. The structural difference in BP and BPN particles further extended to their dissociated disks, which makes the cargo (like R6G) loaded on these disks to show a different stability in acetone. This study demonstrated that a subtle structural change can greatly affect their properties.