Abstract
This study demonstrates a strategy to control lattice symmetry in a polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer hybridized with a small fraction of NH(2)-tethered Fe(3)O(4) magnetic nanoparticles incorporated within the cylindrical PMMA microdomains. A low-intensity magnetic field (= 350 mT) was applied following large-amplitude oscillatory shear alignment, transforming the shear-aligned hexagonally packed cylinders (HEX) into centered rectangular cylinders (CR) stabilized through microdomain reorientation that relieved chain crowding and stretching of the PS blocks. In contrast, applying the magnetic field to unoriented HEX induced reorganization into lamellae aligned parallel to the field. The lamellar phase represented the thermodynamic equilibrium state, whereas the CR phase was a kinetically stabilized metastable structure governed by the prealigned framework. These findings highlight low-intensity magnetic manipulation as an effective "noncontact tweezer" for tuning lattice symmetry in block copolymers via the interplay of magnetic anisotropy and initial microdomain orientation.