Sprecher
Beschreibung
Block polymers (BCPs) are attractive for developing novel materials due to their tunable properties and self-assembly via block chemistry, composition, and molecular weight. However, to harness the unique properties of BCPs in applications, their self-assembly and ordering on long length scales must be controlled. Unfortunately, practical methods for processing BCPs into materials with long-range order remain limited; for example, techniques like magnetic field alignment are typically infeasible because BCPs are weakly diamagnetic and respond minimally to magnetic fields. However, we discovered that magnetic fields induce unexpected self-assembly and ordering in disordered BCP solutions via a new mechanism distinct from domain alignment. This process effectively converts a “non-magnetic” water-like fluid to a soft solid material using only a weak magnet. Here, the formation of stable ordered phases (cubic, cylinder, networks) causes up to a six order-of-magnitude increase in viscosity and modulus. Using a combination of magnetorheology, small angle x-ray scattering, quasi-elastic neutron scattering, and vibrational spectroscopy, we demonstrate that magnetic fields facilitate these phase transitions by altering polymer-solvent interactions, hydrogen bonding, and polymer and solvent mobility – which in turn modify amphiphile packing. By identifying the molecular-scale mechanisms by which magnetic fields alter solvent structure and interactions with macromolecules in solutions, this work can be leveraged to improve chemical separations and to create new polymeric materials for applications in drug delivery, sensing, and catalyst templates.
This work is supported by the National Science Foundation under Grant No. DMR-2143162. We acknowledge the Australian Centre for Neutron Scattering at ANSTO and the Australian Government through the National Collaborative Research Infrastructure Strategy, in supporting the neutron infrastructure used in this work via ACNS proposal 17038.