Liquid to soft solid transition in block polymers via low strength magnetic fields

Achieving magnetic field-induced orientation in block polymers (BCPs) has typically relied on large field strengths (B≥5 T), the addition of liquid-crystalline (LC) or rod-like blocks, substantial chain anisotropy, or combinations therein. BCP ordering upon application of low-strength fields (≤0.5 T) has only been reported in systems of over 60% wt LC mesogen by mass. Here, we identify substantial field-induced rheological and structural changes in several coil-coil BCP variants using magneto-rheology and small-angle neutron scattering (SANS). Linear viscoelastic temperature ramps combined with B≥0.1 T magnetic field show a liquid to gel transition where the increase by three-to-six orders of magnitude beyond a critical time (t_t). Here, t_t is a function of field strength, polymer concentration and molecular weight, temperature, and ionic strength. The resultant gel state is stable for several hours after field removal, where the structural relaxation time scales with the maximum achieved modulus. SANS detects distinct gelation mechanisms based on BCP variant. In addition to structure enhancement, this approach has the potential to discover new structures not accessible through traditional self-assembly routes with minimal input from external fields.