Effect of rod length on the morphology of block copolymer/magnetic nanorod composites.

The organization of magnetic nanorods in microphase-separated diblock copolymers composed of poly(styrene-b-2-vinylpyridine) (PS-PVP) as a function of rod length and rod concentration was investigated using both transmission electron microscopy and small-angle X-ray scattering. Our results reveal that the nanorods were sequestered into the PVP domains, which is attributed to the preferential interaction between pyridine-tethered nanorods and PVP. Meanwhile, the addition of nanorods in PS-PVP caused chain stretching. To minimize the energy penalty, nanorods tended to align parallel to the interface between PS and PVP to increase the conformational entropy. As the length of nanorods increased, the increasing van der Waals interaction and magnetic interaction caused extensive rod aggregation, which suppressed the domain size of PVP and amplified the local compositional fluctuations. This creates conditions to induce disorder in the polymer morphology and nanorods undergo macrophase separation.