The role of hydrogen bonding and chain configuration in magnetically-induced ordering of block copolymer systems

Block copolymers (BCPs) have sustained academic and industrial interest due to unparalleled tunability in properties for widespread applications; however, inability to control long-range ordering limits their utility. We recently discovered anomalous field-induced phase transitions in industrially-relevant BCP solutions (20-30 wt%) using weak magnetic fields (B > 0.5 T), which can be used to control their self-assembly and long-range ordering. These solutions exhibit an anomalous transition from a low viscosity fluid (10^-2 Pa*s) to an ordered soft solid (10⁵ Pa*s) under weak magnetic fields. To determine the mechanism behind these phase transitions, we systematically studied the role of solvent quality and hydrogen bonding on the magnetorheological response and resulting induced structure. The dynamics of each system during magnetization and subsequent relaxation suggest that hydrogen bonding and induced chain conformation play significant roles in the presence of, and induction time required for, anomalous field-induced behavior. Understanding the mechanism behind this unexpected phase behavior in polymer solutions provides a new strategy for designing and processing advanced BCP materials.