Combining shear and magnetic fields to tune the structure and properties of aqueous polymeric solutions

External stimuli such as electric and magnetic fields are commonly used to impart long-range ordering in diamagnetic block copolymers (BCPs) with anisotropic microstructures via phase alignment. However, we have recently shown that the rheology and microstructure of aqueous solutions of spherical BCP micelles can also be altered with low-intensity magnetic fields (0.1-0.5 T), via a mechanism alternative to alignment. Beyond a critical magnetization time, these low viscosity (~0.01 Pa.s) polymer solutions transform into semisolid gels with 3-6 orders increase in dynamic moduli, at temperatures far below the onset of thermal phase transitions. Small-angle X-ray scattering reveals that the field induces ordered packings of spherical micelles that lead to the observed changes in flow behavior. The transition kinetics, pathway, and ultimate phase formed can be altered by combining flow and magnetic fields or by varying the magnetic flux density, temperature, polymer concentration and salinity. This research demonstrates a facile new way to control the flow properties of polymer solutions by low-intensity magnetic fields.