Particle-size dependent melt viscosity behavior and the properties of three-arm star polystyrene–Fe3O4 composites†
The melt viscosity of three-arm star polystyrene (S3PS)–Fe3O4 nanoparticle composites was studied by means of rheological measurements. The arm molecular weight (Ma) of S3PS (or radius gyration) and the particle size of Fe3O4 (radius (Rp): 3 nm and 44 nm) showed a strong influence on the melt viscosity behavior (at low shear frequencies) of S3PS–Fe3O4 composites. The reinforcement (viscosity increase) was observed in the composites where the Ma was higher than the Mc of PS (Mc: the critical molecular weight for chain entanglement). For Ma < Mc, when the size of Fe3O4 nanoparticles was changed, the melt viscosity of the composites exhibited either plasticization (melt viscosity reduction) or reinforcement. When the content of Fe3O4 was low (1 wt%), the transformation from plasticization to reinforcement behavior could be observed, which strongly depended on the size ratio of the radius of gyration (Rg) of S3PS to the size of nanoparticles (Rp). In addition, the magnetic properties and thermal stability of S3PS–Fe3O4 composites were studied.