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)-Fe(3)O(4) 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 Fe(3)O(4) (radius (R(p)): 3 nm and 44 nm) showed a strong influence on the melt viscosity behavior (at low shear frequencies) of S3PS-Fe(3)O(4) 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 Fe(3)O(4) nanoparticles was changed, the melt viscosity of the composites exhibited either plasticization (melt viscosity reduction) or reinforcement. When the content of Fe(3)O(4) 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-Fe(3)O(4) composites were studied.