Particle-size dependent melt viscosity behavior and the properties of three-arm star polystyrene–Fe3O4 composites

Abstract

The melt viscosity of three-arm star polystyrene (S3PS)–Fe₃O₄ nanoparticle composites was studied by means of rheological measurements. The arm molecular weight (M_a) of S3PS (or radius gyration) and the particle size of Fe₃O₄ (radius (R_p): 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 M_a was higher than the M_c of PS (M_c: the critical molecular weight for chain entanglement). For M_a < M_c, 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 (R_g) of S3PS to the size of nanoparticles (R_p). In addition, the magnetic properties and thermal stability of S3PS–Fe₃O₄ composites were studied.