The dispersion state of magnetic nanorods in homopolymers and block copolymers

We investigated the dispersion state of pyridine-modified magnetic nanorods in poly(2 vinylpyridine) (P2VP) homopolymers and poly(styrene-b-2 vinylpyridine) (PS-P2VP) diblock copolymers. In the P2VP/nanorod mixtures, the dispersion of nanorods was enhanced in systems in which the molecular weight of P2VP was increased because the long P2VP chains provided steric hindrance and thus screened the attractive interparticle interactions, inhibiting the rod aggregation. When nanorods were mixed with PS-P2VP, the phase stability of the mixtures varied considerably according to changes in the lamellar period of PS-P2VP (D). When D was large, nanorods were sequestered into the P2VP domains through enthalpically driven self-assembly, and the nanorods became spatially organized. By contrast, when D was small, the introduction of nanorods caused substantial distortion of chain conformations. This entropically unfavorable condition can be offset by excluding nanorods from the ordered phases, causing particle aggregation. At a high particle loading, the attractive interparticle interactions outweighed the particle-polymer interaction and entropic contribution of polymers. Consequently, nanorods underwent extensive aggregation.