Tuning block copolymer rheology and structure via low strength magnetic fields

The control of block polymer (BCP) structural ordering is of significant scientific interest because of their wide applications including nanotemplates, drug delivery and biomineralization. BCP properties have been controlled using various external fields including electric, magnetic, and shear fields, and via plasticizing additives, interfacial effects, and thermal methods. To control ordering in BCPs using magnetic fields, previous studies had used field strengths (≥5T), liquid crystalline mesogens, high magnetic susceptibility anisotropy groups or combinations therein. Here, we show anomalous behavior upon application of low strength magnetic fields (≥0.1 T) in coil-coil BCPs. Magneto-shear rheology shows up to a six order increase in modulus upon the field application. This magnetic response is a function of temperature, concentration, field strength, ionic content and shear strain. A minimum molecular weight and block length are required for this liquid to gel transition via low strength magnetic field. In situ small angle scattering (SAXS and SANS) and imaging techniques showed field-induced orientation in the BCPs and this orientation direction can be tuned by changing the direction of field lines.