Interfacial Engineering of Block Copolymer Nanostructures: Morphology and Solvent Stability

Interfacial engineering is a critical pathway for modulatingtheself-assembled nanostructures of block copolymers (BCPs) during solventexchange. Herein, we demonstrated the generation of different stackedlamellae of polystyrene-block-poly(2-vinyl pyridine)(PS-b-P2VP) nanostructures during solvent exchangeby using phosphotungstic acid (PTA) or PTA/NaCl aqueous solution asthe nonsolvent. The participation of PTA in the confined microphaseseparation of PS-b-P2VP in droplets increases thevolume fraction of P2VP and decreases the tension at the oil/waterinterface. Moreover, the addition of NaCl to the PTA solution canfurther increase the surface coverage of P2VP/PTA on droplets. Allfactors impact the morphology of assembled BCP nanostructures. Inthe presence of PTA, ellipsoidal particles composed of alternativelystacked lamellae of PS and P2VP were formed (named BP), whereas, inthe coexistence of PTA and NaCl, they changed to stacked disks withPS-core-P2VP-shell (called BPN). The different structures ofassembled particles induce their different stabilities in solventsand different dissociation conditions as well. The dissociation ofBP particles was easy because PS chains were only entangled togetherwhich can be swollen in toluene or chloroform. However, the dissociationof BPN was hard, requiring an organic base in hot ethanol. The structuraldifference in BP and BPN particles further extended to their dissociateddisks, which makes the cargo (like R6G) loaded on these disks to showa different stability in acetone. This study demonstrated that a subtlestructural change can greatly affect their properties.