Dynamics of Magnetic Alignment in Rod–Coil Block Copolymers

The dynamics associated with magnetic field alignment of a model rod–coil block copolymer poly(2,5-di(2′-ethylhexyloxy)-1,4-phenylenevinylene)-b-polyisoprene (PPV–PI) have been investigated using a combination of time-resolved in situ small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Alignment is observed over a wide range of field strengths (0.2–7 T); however, the highest field strengths studied produce the highest degree of alignment. Experiments examining alignment of a disordered sample, cooled into the ordered state in the presence of a magnetic field, show that alignment mostly occurs during nucleation and growth of the block copolymer nanostructure. The slower secondary processes of defect annihilation and grain rotation progress are necessary in producing extremely highly aligned samples. At the highest field strength, due to the increased order–disorder transition temperature (TODT), selective ordering is likely observed at temperatures near the order–disorder transi...